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Boundary Layer Turbulence Index: Progress and Recent Developments
Pryor, Kenneth L
A boundary layer turbulence index (TIBL) product has been developed to assess the potential for turbulence in the lower troposphere, generated using RUC-2 numerical model data. The index algorithm approximates boundary layer turbulent kinetic energy by parameterizing vertical wind shear, responsible for mechanical production of TKE, and kinematic heat flux, parameterized by the vertical temperature lapse rate and responsible for buoyant production of TKE. Validation for the TIBL product has been conducted for selected nonconvective wind events during the 2008 winter season over the Idaho National Laboratory mesonet domain. This paper presents studies of four significant wind events between December 2007 and February 2008 over southeastern Idaho. Based on the favorable results highlighted from validation statistics and in the case studies, the RUC TIBL product has demonstrated operational utility in assessing turbulence hazards to low-flying aircraft and ground transportation, and in the assessment of wildfire...
The nonlinear development of Gortler vortices in growing boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip
The development of Gortler vortices in boundary layers over curved walls in the nonlinear regime is investigated. The growth of the boundary layer makes a parallel flow analysis impossible except in the high wavenumber regime so in general the instability equations must be integrated numerically. Here the spanwise dependence of the basic flow is described using Fourier series expansion whilst the normal and streamwise variations are taken into account using finite differences. The calculations suggest that a given disturbance imposed at some position along the wall will eventually reach a local equilibrium state essentially independent of the initial conditions. In fact, the equilibrium state reached is qualitatively similar to the large amplitude high wave-number solution described asymptotically by Hall (1982). In general, it is found that the nonlinear interactions are dominated by a mean field type of interaction between the mean flow and the fundamental. Thus, even though higher harmonics of the fundamental are necessarily generated, most of the disturbance energy is confined to the mean flow correction and the fundamental. A major result of the calculations is finding that the downstream velocity field develops a strongly inflection character as the flow moves downstream. The latter result suggests that the major effect of Gortler vortices on boundary layers of practical importance might be to make them highly receptive to rapidly growing Rayleigh modes of instability.
LASE measurements of convective boundary layer development during SGP97
NASA Technical Reports Server (NTRS)
Ismail, Syed; Browell, Edward V.; Ferrare, Richard A.; Senff, Christoph; Davis, Kenneth J.a; Lenschow, Donald H.; Kooi, Susan; Brackett, Vince; Clayton, Marian
The Southern Great Plains 1997 (SGP97) field experiment was conducted in Oklahoma during June-July 1997 to validate the models used for computing remote soil moisture using measurements by microwave radiometers. One of the objectives of SGP97 was to examine the effect of soil moisture on the evolution of the Atmospheric Boundary Layer (ABL) and clouds over the Southern Great Plains (SGP) during the warm season. The LASE (Lidar Atmospheric Sensing Experiment) airborne DIAL (Differential Absorption Lidar) system, which was flown autonomously on the NASA ER-2 aircraft during previous missions, was reconfigured to fly on the NASA P3 research aircraft. During SGP97 LASE was used to study the morning evolution of the ABL, particularly as manifested in the development of the convective boundary layer, and to study the influence of soil moisture variations on the development of ABL. The ABL development is strongly influenced by the surface energy budget, which is in turn influenced by soil moisture, mesoscale meteorology, clouds, and solar insolation. LASE data acquired during this mission are being used to study the ABL water vapor budget, the development of the ABL, spatial and temporal variabilities in the ABL, and the meteorological factors that influence the ABL development. This field experiment also permitted comparisons of LASE water vapor measurements with water vapor profiles acquired by radiosondes launched at the DOE (Department of Energy) Atmospheric Radiation Measurement (ARM) Southern Great Plain (SGP) site and at NASA/Wallops Flight Facility, as well as with measurements from other SGP97 aircraft.
Generation of Turbulent Inflow Data for Spatially-Developing Boundary Layer Simulations
Thomas S. Lund; Xiaohua Wu; Kyle D. Squires
A method for generating three-dimensional, time-dependent turbulent inflow data for simulations of complex spatially developing boundary layers is described. The approach is to extract instantaneous planes of velocity data from an auxiliary simulation of a zero pressure gradient boundary layer. The auxiliary simulation is also spatially developing, but generates its own inflow conditions through a sequence of operations where the
Ventilated oscillatory boundary layers
NASA Astrophysics Data System (ADS)
Conley, Daniel C.; Inman, Douglas L.
A combination of field and laboratory experiments are made in order to expand our knowledge of naturally occurring oscillatory boundary layers. Chapter 1 describes field observations of the development of wave driven boundary layers at the fluid sediment interface. Under the crest of the wave, this development can be idealized as an identifiable sequence of three parts. The latter parts of this development are never observed to occur under the trough of the wave despite similarities in wave orbital velocity and acceleration. It is proposed that wave induced boundary ventilation, the oscillatory flow through the surface of a permeable bed, may be responsible for this apparent developmental asymmetry. In chapter 2, a laboratory study is presented of ventilated oscillatory boundary layers. These are boundary layers arising from a flow which oscillates parallel to a permeable bed which is subject to oscillating percolation of the same frequency as the bed parallel flow. Measurements of boundary layer velocities, bed stress and turbulent flow properties are presented. It is observed that suction (flow into the bed) enhances the near bed velocities and bed stress while injection (flow out of the bed) leads to a reduction in these quantities. As the ventilated oscillatory boundary layer experiences both these phenomena in one full cycle, the result is a net stress and a net boundary layer velocity in an otherwise symmetric flow. While production of turbulence attributable to injection is enhanced, the finite time required for this to occur leads to greater vertically averaged turbulence in the suction half cycle. Turbulence generated in the suction half cycle is maintained in a compact layer much closer to the bed. These effects appear to hold for Re ranging from 10(exp 5) to 10(exp 6) and for oscillations other than sinusoidal.
Further development and testing of a second-order bulk boundary layer model. Master's thesis
Krasner, R.D.
A one-layer bulk boundary layer model is developed. The model predicts the mixed layer values of the potential temperature, mixing ratio, and u- and v-momentum. The model also predicts the depth of the boundary layer and the vertically integrated turbulence kinetic energy (TKE). The TKE is determined using a second-order closure that relates the rate of dissipation to the TKE. The fractional area covered by rising motion sigma and the entrainment rate (E) are diagnostically determined. The model is used to study the clear convective boundary layer (CBL) using data from the Wangara, Australia boundary layer experiment. The Wangara data is also used as an observation base to validate model results. A further study is accomplished by simulating the planetary boundary layer (PBL) over an ocean surface. This study is designed to find the steady-state solutions of the prognostic variable.
Hypersonic Boundary-Layer Trip Development for Hyper-X
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Auslender, Aaron H.; Dilley, Authur D.; Calleja, John F.
Boundary layer trip devices for the Hper-X forebody have been experimentally examined in several wind tunnels. Five different trip configurations were compared in three hypersonic facilities, the LaRC 20-Inch Mach 6 Air Tunnel, the LaRC 31 -Inch Mach 10 Air Tunnel, and in the HYPULSE Reflected Shock Tunnel at GASL. Heat transfer distributions, utilizing the phosphor thermography and thin-film techniques, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. Parametric variations include angles-of-attack of 0-deg, 2-deg, and 4-deg; Reynolds numbers based on model length of 1.2 to 15.4 million: and inlet cowl door simulated in both open and closed positions. Comparisons of transition due to discrete roughness elements have led to the selection of a trip configuration for the Hyper-X Mach 7 flight vehicle.
Spatially Developing Secondary Instabilities in Compressible Swept Airfoil Boundary Layers
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan M.
Two-dimensional eigenvalue analysis is used on a massive scale to study spatial instabilities of compressible shear flows with two inhomogeneous directions. The main focus of the study is crossflow dominated swept-wing boundary layers although the methodology can also be applied to study other type of flows, such as the attachment-line flow. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed, namely, fixing the spatial growth direction unambiguously through a non-orthogonal formulation of the linearized disturbance equations. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined.
Boundary layer development in axial compressors and turbines. Part 4 of 4: Computations and analyses
Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)
This is Part Four of a four-part paper. It begins with Section 16.0 and concludes the description of the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this paper, the computational predictions made using several modern boundary layer codes are presented. Both steady codes and an unsteady code were evaluated. The results are compared with time-averaged and unsteady integral parameters measured for the boundary layers. Assessments are made to provide guidance in using the predictive codes to locate transition and predict loss. Conclusions from the computational analyses are then presented.
Sink flow turbulent boundary layers
M. B. Jones; Ivan Marusic; A. E. Perry
An experimental investigation of turbulent boundary layers developing in a sink flow pressure gradient was undertaken. Three flow cases were studied, corresponding to acceleration strengths K=5.4�10-7 3.6�10-7 and 2.7�10-7. Sink flow boundary layers are of fundamental importance, as they represent the only smooth wall boundary layer that may evolve to a state of precise equilibrium. A precise equilibrium layer is
Variations in the ozone concentration during the boundary layer development over urban area
NASA Astrophysics Data System (ADS)
Kolev, Nikolay; Grigorieva, Vera; Kaprielov, Boiko; Kolev, Ivan
Some results obtained during two campaigns (summer 2004 and autumn 2005) of observation of the planetary boundary layer dynamics over the urban area of the Sofia city are presented. An EARLINET scanning aerosol lidar, an ozone analyzer and a ground meteorological station were used during the observations. Particularly, the mixing layer development and the residual layer destruction along with the relevant ground level ozone concentration variation followed during the convective boundary layer formation in two situations (in the case of a partial solar eclipse, and in the case of atmospheric internal gravity waves presence) are presented and considered.
Stratified Atmospheric Boundary Layers
L. Mahrt
Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet,
Off-Body Boundary-Layer Measurement Techniques Development for Supersonic Low-Disturbance Flows
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Kegerise, Michael A.; Wilkinson, Stephen P.
Investigations were performed to develop accurate boundary-layer measurement techniques in a Mach 3.5 laminar boundary layer on a 7 half-angle cone at 0 angle of attack. A discussion of the measurement challenges is presented as well as how each was addressed. A computational study was performed to minimize the probe aerodynamic interference effects resulting in improved pitot and hot-wire probe designs. Probe calibration and positioning processes were also developed with the goal of reducing the measurement uncertainties from 10% levels to less than 5% levels. Efforts were made to define the experimental boundary conditions for the cone flow so comparisons could be made with a set of companion computational simulations. The development status of the mean and dynamic boundary-layer flow measurements for a nominally sharp cone in a low-disturbance supersonic flow is presented.
Boundary layer development in axial compressors and turbines. Part 1 of 4: Composite picture
Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)
Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components.Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of the experimental findings by using sketches to show how boundary layers develop on compressor and turbine blading. Parts 2 and 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and discusses comparisons with experimental data. Readers not interested in experimental detail can go directly from Part 1 to Part 4.
Development of a Boundary Layer Property Interpolation Tool in Support of Orbiter Return To Flight
NASA Technical Reports Server (NTRS)
Greene, Francis A.; Hamilton, H. Harris
A new tool was developed to predict the boundary layer quantities required by several physics-based predictive/analytic methods that assess damaged Orbiter tile. This new tool, the Boundary Layer Property Prediction (BLPROP) tool, supplies boundary layer values used in correlations that determine boundary layer transition onset and surface heating-rate augmentation/attenuation factors inside tile gouges (i.e. cavities). BLPROP interpolates through a database of computed solutions and provides boundary layer and wall data (delta, theta, Re(sub theta)/M(sub e), Re(sub theta)/M(sub e), Re(sub theta), P(sub w), and q(sub w)) based on user input surface location and free stream conditions. Surface locations are limited to the Orbiter s windward surface. Constructed using predictions from an inviscid w/boundary-layer method and benchmark viscous CFD, the computed database covers the hypersonic continuum flight regime based on two reference flight trajectories. First-order one-dimensional Lagrange interpolation accounts for Mach number and angle-of-attack variations, whereas non-dimensional normalization accounts for differences between the reference and input Reynolds number. Employing the same computational methods used to construct the database, solutions at other trajectory points taken from previous STS flights were computed: these results validate the BLPROP algorithm. Percentage differences between interpolated and computed values are presented and are used to establish the level of uncertainty of the new tool.
Quadrant Analysis of the Heat and Momentum Fluxes at the Transition Layer between the Marine Atmospheric Boundary Layer and the developed Internal Boundary Layer close to the coastline
NASA Astrophysics Data System (ADS)
Panagiotis Raptis, Ioannis; Helmis, Constantinos
The purpose of this work is to study the main characteristics and the micro-structure of the Transition Layer between the Marine Atmospheric Boundary Layer (MABL) and the developed Internal Boundary Layer (IBL), which is created downwind close to the coastline. The dynamics and the structure of this Transition Layer, which could be defined as the region where the growing IBL perturbations enter the MABL and mix the air, are of major interest affecting a variety of MABL' parameters. For this study data collected from CBLAST field campaign, conducted during summer 2003 at Nantucket Island USA, were used. More specifically data from sonic anemometer measurements at 20 Hz sampling frequency, at 10m height and 80m distance from the coastline were studied. According to our measurements during the night the recorded characteristics of the surface layer at 10m height had the behavior of the MABL, while during the day in most cases the developed IBL was recorded. Thus a diurnal cycle was noticed with the mechanically generated IBL during the night, being lower than the height of our instruments (10m) while a thermally generated IBL during the day was easily observed with characteristic perturbations. In many cases an intermediate state was observed, indicating the existence of the Transition Layer. In order to identify the layers and their characteristics, a conditional analysis was developed using multiple criteria, based mainly on values of the heat and momentum fluxes estimated by the eddy covariance method. We used the quadrant analysis method to study the coherent structures and compare the results under different atmospheric conditions. This method decomposes shear stress into four quadrants, separating the events that contribute to the downward and upward momentum fluxes. Events in quadrants 2 (ejections) and 4 (sweeps) compose the coherent turbulent structures while events in quadrants 1 and 3 compose the incoherent structures. The parameters ? and exuberance provide info on the relation between the ejection and the sweep mechanisms and coherent/incoherent structures accordingly. Within the IBL layer the ejections are the governing state, implying that they are the dominant mechanism of the growing layer, where the more powerful eddies are sweeping mass from the overlaying layer. Within the MABL layer a more balanced state between ejections/sweeps is observed implying that the MABL is more stable energy is more equilibrated and there are more incoherent motions. At the Transition Layer, we recorded more ejections than sweeps, but less than within the IBL. In that case it seems that an invasion of strong eddies from the underlying layer to the stable layer is the main mechanism. By concluding, the Transition Layer features significantly different behavior compared with the pure MABL and IBL layers, thus a separate study of the structure of this zone could enhance the knowledge of the turbulent processes of a growing layer and explain the complicated states observed in field experiments.
Developing mass spectrometric techniques for boundary layer measurement in hypersonic high enthalpy test facilities
NASA Technical Reports Server (NTRS)
Wood, G. M., Jr.; Lewis, B. W.; Nowak, R. J.; Eide, D. G.; Paulin, P. A.; Upchurch, B. T.
Thermodynamic flow properties of gases in the boundary layer or the flowfield have been mainly deduced from pressures and temperatures measured on a model. However, further progress with respect to an understanding of these properties requires a more complete characterization of the layer including determination of the gas composition and chemistry. Most attempts to measure boundary layer chemistry involve the employment of a mass spectrometer and an associated gas sampling system. The three major limiting factors which must be addressed for species measurement in aerothermodynamic investigations on models at reentry stream velocities, are gas sampling effects, instrument limitations, and problems with data acquisition. The present investigation is concerned with a concentrated effort to quantitatively identify and correct for instrument and sampling system effects, and to develop a miniaturized high performance mass spectrometer for on-model real-time analysis of the boundary layer and its associated atmosphere.
The fully nonlinear development of Goertler vortices in growing boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip; Lakin, William D.
The fully nonlinear development of small wavelength Goertler vortices in a growing boundary layer is investigated using a combination of asymptotic and numerical methods. The starting point for the analysis is the weakly nonlinear theory of Hall (1982b) who discussed the initial development of small amplitude vortices in a neighborhood of the location where they first become linearly unstable. That development is unusual in the context of nonlinear stability theory in that it is not described by the Stuart-Watson approach. In fact the development is governed by a pair of coupled nonlinear partial differential evolution equations for the vortex flow and the mean flow correction. Here the further development of this interaction is considered for vortices so large that the mean flow correction driven by them is as large as the basic state. Surprisingly it is found that such a nonlinear interaction can still be described by asymptotic means. It is shown that the vortices spread out across the boundary layer and effectively drive the boundary layer. In fact the system obtained by writing down the equations for the fundamental component of the vortex generate a differential equation for the basic state. Thus the mean flow adjusts so as to make these large amplitude vortices locally neutral. Moreover in the region where the vortices exist the mean flow has a square-root profile and the vortex velocity field can be written down in closed form. The upper and lower boundaries of the region of vortex activity are determined by a free-boundary problem involving the boundary layer equations. In general it is found that this region ultimately includes almost all of the original boundary layer and much of the free-stream. In this situation the mean flow has essentially no relationship to the flow which exists in the absence of the vortices.
The atmospheric boundary layer
J. R. Garratt
In this book, the author successfully reviews the current state of affairs in boundary-layer meteorology research. The book is organized into nine chapters. The first chapter is an introduction to the topic of the atmospheric boundary layer. The second chapter is a survey of turbulence theory. The third chapter reviews the similarity relationships that have been formulated for the various
The Atmospheric Boundary Layer
ERIC Educational Resources Information Center
Tennekes, Hendrik
Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)
Reynolds shear stress development in pressure-driven three-dimensional turbulent boundary-layers
NASA Technical Reports Server (NTRS)
Anderson, S. D.; Eaton, J. K.
The development of the Reynolds stresses has been examined experimentally in an initially two-dimensional boundary layer which is driven to three dimensionality by a spanwise pressure gradient. The pressure field was imposed by an upstream-facing wedge. Two different wedge angles were used in order to vary the level of boundary layer skewing. Bradshaw's Al parameter was found to decrease with the rate of decrease being dependent on the level of skewing between the freestream and the wall flow. It was also concluded that the ratio of the cross-stream to streamwise shear stress components was governed by the rate of freestream turning.
An experimental study of the development of longitudinal vortex pairs embedded in a turbulent boundary layer
NASA Technical Reports Server (NTRS)
Pauley, Wayne R.; Eaton, John K.
The mean streamwise development of pairs of longitudinal vortices embedded in an otherwise two-dimensional turbulent boundary layer was studied. Planes of closely spaced measurements of the three components of mean velocity were obtained at several streamwise locations, and the vorticity and circulation were calculated. Skin-friction measurements were also made. It was found that the rate of vorticity spreading in a vortex was greatly increased by close proximity of other vortices. The rate of streamwise circulation decrease was significantly greater for corotating vortices than for counter rotating vortices. Boundary-layer thinning and increased skin friction occured in regions where the secondary flow induced by the pairs was directed toward the wall; the boundary layer was thickened and skin friction reduced where the secondary flow was directed away from the wall.
Boundary Layer Energy Transport and Cumulus Development over a Heated Mountain: An Observational Study
Geerts, Bart
Boundary Layer Energy Transport and Cumulus Development over a Heated Mountain: An Observational Creighton University, Omaha, Nebraska (Manuscript received 27 November 2007, in final form 2 July 2008 in Arizona, 2030 km in diameter, during the North American monsoon, on days with weak winds and cumulus
On the development of boundary layer secondary circulations resulting from horizontally varying surface heat flux
Shaw, W.J.; Doran, J.C.
During the last decade there has been a surge in efforts to understand the processes at work in the inhomogeneous atmospheric boundary layer. Much of the interest in the problem has been driven by increasingly urgent needs to develop accurate assessments of man`s Contribution to climate change. It has been argued that subgrid-scale secondary circulations in the boundary layer can cause significant errors in parameterized turbulent surface fluxes. Such circulations -- variously termed ``inland breezes``, ``lake breezes``, ``snow breezes``, or ``nonclassical mesoscale circulations`` are becoming widely discussed and modeled. Because surface fluxes are part of the lower boundary condition for global climate models, it is important to understand when these circulations occur and what their effects are on overall turbulent transfer. What are not yet clear are the combinations of the ambient wind and the horizontal scale and intensity of surface flux variability under which we may expect boundary layer secondary circulations to occur. Several authors have modeled the development of these circulations for ad hoc situations of alternating surface characteristics, and SA have developed one parameterization relating the scale of surface heat flux variability and the ambient wind to the evolution of NCMCs. In this paper we present observations, collected in a region of inhomogeneous surface fluxes, that suggest the development of a ``farm breeze``, and we develop an alternative scaling argument to that of SA that better represents our measurement conditions.
Field evidence of the viscous sublayer in a tidally forced developing boundary layer
NASA Astrophysics Data System (ADS)
Wengrove, M. E.; Foster, D. L.
Field observations of boundary layer development within a tidally forced estuary revealed evidence of an observable viscous sublayer. Evidence is provided by several independent measures of the flow field, including hydrodynamic smoothness, an immobile bed, and characteristic velocity, constant stress, and higher-order moment structures. This investigation reports what may be the second comprehensive observation of the viscous sublayer in a marine environment, and what could be the first observation of a momentum balance that includes the viscous sublayer within a shallow estuarine environment. Hydrodynamic observations were made in a straight channel within the Great Bay Estuary of New Hampshire over a flat sandy mud with low water depth of 1.5 m at the sampling location. Beyond quantifying the role of the benthic boundary layer in nutrient dynamics, these observations are useful to provide insight into very near boundary stress estimates leading to incipient motion in estuarine and coastal environments.
Reynolds stress development in pressure-driven three-dimensional turbulent boundary layers
NASA Technical Reports Server (NTRS)
Anderson, Shawn D.; Eaton, John K.
The development of the Reynolds stress field was studied for flows in which an initially two-dimensional boundary layer was skewed sideways by a spanwise pressure gradient ahead of an upstream-facing wedge. Two different wedges were used, providing a variation in the boundary-layer skewing. Measurements of all components of the Reynolds stress tensor and all ten triple products were measured using a rotatable cross-wire anemometer. The results show the expected lag of the shear stress vector behind the strain rate. Comparison of the two present experiments with previous data suggests that the lag can be estimated if the radius of curvature of the free-stream streamline is known. The magnitude of the shear stress vector in the plane of the wall is seen to decrease rapidly as the boundary-layer skewing increases. The amount of decrease is apparently related to the skewing angle between the wall and the free stream. The triple products evolve rapidly and profiles in the three-dimensional boundary layer are considerably different than two-dimensional profiles, leaving little hope for gradient transport models for the Reynolds stresses. The simplified model presented by Rotta (1979) performs reasonably well providing that an appropriate value of the T-parameter is chosen.
Boundary layer transition studies
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.
The development of a low velocity wind tunnel with instrumentation for boundary layer investigations
Massey, John Robert
fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 1958 Major Subject: Mechanical Engineering THE DEVELOPMENT OF A LOW VELOCITY WIND TUNNEL WITH INSTRUMENTATION FOR BOUNDARY LAYER INVESTIGATIONS A Dissertation By John Robert.... The writer is also appreciative of the assistance given by Dr. J. D. Lindsay, Graduate School Representative, and Dr. C. M. Simmang, Head of the Department of Mechanical Engineering, The writer wishes to express much gratitude to Warren Rice, principal...
Boundary layer development in axial compressors and turbines. Part 2 of 4: Compressors
Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)
This is Part Two of a four-part paper. It begins with Section 6.0 and continues to describe the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this part, the authors present the experimental evidence used to construct the composite picture for compressors given in the discussion in Section 5.0 of Part 1. They show the data from the surface hot-film gages and the boundary layer surveys, give a thorough interpretation for the baseline operating condition, and then show how this picture changes with variations in Reynolds number, airfoil loading, frequency of occurrence of wakes and wake turbulence intensity. Detailed flow features are described using raw time traces. The use of rods to simulate airfoil wakes is also evaluated.
Study of Boundary Layer Development in a Two-Stage Low-Pressure Turbine
NASA Technical Reports Server (NTRS)
Dorney, Daniel J.; Ashpis, David E.; Halstead, David E.; Wisler, David C.
Experimental data from jet-engine tests have indicated that unsteady blade row interactions and separation can have a significant impact on the efficiency of low-pressure turbine stages. Measured turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Several recent studies have revealed that Reynolds number effects may contribute to the lower efficiencies at cruise conditions. In the current study numerical simulations have been performed to study the boundary layer development in a two-stage low-pressure turbine, and to evaluate the transition models available for low Reynolds number flows in turbomachinery. The results of the simulations have been compared with experimental data, including airfoil loadings and integral boundary layer quantities. The predicted unsteady results display similar trends to the experimental data, but significantly overestimate the amplitude of the unsteadiness. The time-averaged results show close agreement with the experimental data.
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.
Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.
The Effects of Blade Count on Boundary Layer Development in a Low-Pressure Turbine
NASA Technical Reports Server (NTRS)
Dorney, Daniel J.; Flitan, Horia C.; Ashpis, David E.; Solomon, William J.
Experimental data from jet-engine tests have indicated that turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Recent studies have shown that Reynolds number effects contribute to the lower efficiencies at cruise conditions. In the current study numerical simulations have been performed to study the boundary layer development in a two-stage low-pressure turbine, and to evaluate the models available for low Reynolds number flows in turbomachinery. In a previous study using the same geometry the predicted time-averaged boundary layer quantities showed excellent agreement with the experimental data, but the predicted unsteady results showed only fair agreement with the experimental data. It was surmised that the blade count approximation used in the numerical simulations generated more unsteadiness than was observed in the experiments. In this study a more accurate blade approximation has been used to model the turbine, and the method of post-processing the boundary layer information has been modified to more closely resemble the process used in the experiments. The predicted results show improved agreement with the unsteady experimental data.
Direct numerical simulation of spatially developing turbulent boundary layers with opposition control
NASA Astrophysics Data System (ADS)
Xia, Qian-Jin; Huang, Wei-Xi; Xu, Chun-Xiao; Cui, Gui-Xiang
Opposition control of spatially developing turbulent boundary layers for skin friction drag reduction is studied by direct numerical simulations. The boundary layer extends 800?0 in the streamwise (x) direction, with ?0 denoting the momentum thickness at the flow inlet. The Reynolds number, based on the external flow velocity and the momentum thickness, ranges from 300 to 860. Opposition control applied in different streamwise ranges, i.e. 200\\lt x/{{? }0}\\lt 350 and 200\\lt x/{{? }0}\\lt 550, as well as the uncontrolled case, are simulated. Statistical results and instantaneous flow fields are presented, with special attention paid to the spatial evolution properties of the boundary layer flow with control and the underlying mechanism. It is observed that a long spatial transient region after the control start and a long recovery region after the control end are present in the streamwise direction. A maximum drag reduction rate of about 22% is obtained as the transient region is passed, and an overshoot in the local skin friction coefficient (Cf) occurs in the recovery region. A new identity is derived for dynamical decomposition of Cf. Reduction of Cf by opposition control and overshoot of Cf in the recovery region are explained by quantifying the contributions from the viscous shear stress term, the Reynolds shear stress term, the mean convection term and other terms.
Boundary-layer Development and Skin Friction at Mach Number 3.05
NASA Technical Reports Server (NTRS)
Brinich, Paul F; Diaconis, Nick S
Experimental and theoretical results are presented for boundary layer studies consisting of Schlieren observations and momentum surveys made on hollow cylinder models with their axes aligned parallel to the stream. Results were obtained for three model diameters and for natural and artificially induced turbulent boundary layer flows.
Development of Prediction Method of Boundary Layer Bypass Transition using Intermittency Transport Equation
Nasrin Akhter; Funazaki Ken-ichi
This paper presents a new RANS-based method for predicting bypass transition of the boundary layer using intermittency transport equation. The base program is based on the boundary-layer analysis code given by Schmidt and Patankar (1988), implemented with Myong-Kasagi k ? ? turbulence model. The intermittency transport equation proposed in this study is the modification of Cho and Chung model (1992)
Turbulent properties of a wind-turbine wake developed in a boundary layer flow
Leonardo Chamorro; Fernando Porte-Agel
Wind turbine wake characteristics are expected to depend on the incoming atmospheric boundary layer flow statistics (e.g., mean velocity distribution, turbulent stresses and turbulent fluxes). Atmospheric stability is also expected to affect the structure of a turbine wake. In this study, results are presented from wind tunnel experiments carried out at the St. Anthony Falls Laboratory atmospheric boundary layer wind
T. E. Eastman; L. A. Frank; W.K. Peterson; W. Lennartsson
The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three-dimensional velocity-space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockhead ion mass spectrometers indicate that ionospheric ions play a crucial
NASA Astrophysics Data System (ADS)
Costigliola, V.
It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate matter for regional environmental agencies - Local forecast model evaluation support for local authorities and city bodies. Giving value to the above listed aspects, PASODOBLE objectives are following: - Evolution of existing and development of new sustainable air quality services for Europe on regional and local scales - Development and testing of a generic service framework for coordinated input data acquisition and customizable user-friendly access to services - Utilization of multiple cycles of delivery, use and assessment versus requirements and market planning in cooperation with users - Promotion and harmonisation of best practise tools for air quality communities. Further European multidisciplinary projects should be created to better understand the most prevalent atmospheric factors to be impacted in predictive, preventive and personalised medicine considered as the central concept for future medicine.
Nonequilibrium chemistry boundary layer integral matrix procedure
NASA Technical Reports Server (NTRS)
Tong, H.; Buckingham, A. C.; Morse, H. L.
The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.
Development of efficient GPU parallelization of WRF Yonsei University planetary boundary layer scheme
NASA Astrophysics Data System (ADS)
Huang, M.; Mielikainen, J.; Huang, B.; Chen, H.; Huang, H.-L. A.; Goldberg, M. D.
The planetary boundary layer (PBL) is the lowest part of the atmosphere and where its character is directly affected by its contact with the underlying planetary surface. The PBL is responsible for vertical sub-grid-scale fluxes due to eddy transport in the whole atmospheric column. It determines the flux profiles within the well-mixed boundary layer and the more stable layer above. It thus provides an evolutionary model of atmospheric temperature, moisture (including clouds), and horizontal momentum in the entire atmospheric column. For such purposes, several PBL models have been proposed and employed in the weather research and forecasting (WRF) model of which the Yonsei University (YSU) scheme is one. To expedite weather research and prediction, we have put tremendous effort into developing an accelerated implementation of the entire WRF model using Graphics Processing Unit (GPU) massive parallel computing architecture whilst maintaining its accuracy as compared to its CPU-based implementation. This paper presents our efficient GPU-based design on WRF YSU PBL scheme. Using one NVIDIA Tesla K40 GPU, the GPU-based YSU PBL scheme achieves a speedup of 193� with respect to its Central Processing Unit (CPU) counterpart running on one CPU core, whereas the speedup for one CPU socket (4 cores) with respect to one CPU core is only 3.5�. We can even boost the speedup to 360� with respect to one CPU core as two K40 GPUs are applied.
Development and Breakdown of Goertler Vortices in High Speed Boundary Layers
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; Wu, Minwei; Greene, Ptrick T.
The nonlinear development of G rtler instability over a concave surface gives rise to a highly distorted stationary flow in the boundary layer that has strong velocity gradients in both spanwise and wall-normal directions. This distorted flow is susceptible to strong, high frequency secondary instability that leads to the onset of transition. For high Mach number flows, the boundary layer is also subject to the second mode instability. The nonlinear development of G rtler vortices and the ensuing growth and breakdown of secondary instability, the G rtler vortex interactions with second mode instabilities as well as oblique second mode interactions are examined in the context of both internal and external hypersonic configurations using nonlinear parabolized stability equations, 2-D eigenvalue analysis and direct numerical simulation. For G rtler vortex development inside the Purdue Mach 6 Ludwieg tube wind tunnel, multiple families of unstable secondary eigenmodes are identified and their linear and nonlinear evolution is examined. The computation of secondary instability is continued past the onset of transition to elucidate the physical mechanisms underlying the laminar breakdown process. Nonlinear breakdown scenarios associated with transition over a Mach 6 compression cone configuration are also explored.
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.
High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.
Numerical simulation of internal boundary-layer development and comparison with atmospheric data
J�nos J�zsa; Barbara Milici; Enrico Napoli
A finite-volume numerical model is employed to investigate the adaptation of the atmospheric boundary layer to a change in\\u000a the underlying surface roughness, such as that existing in the transition from land to the free surface of a water body. Numerical\\u000a results are validated by comparison with neutral stratification atmospheric data and compared with the internal boundary-layer\\u000a (IBL) heights computed
Near-field measurements and development of a new boundary layer over a flat plate with localized suction
Amit Agrawal; Lyazid Djenidi; R. A. Antonia
Suction on a turbulent boundary layer is applied through a narrow strip in order to understand the effects suction can have\\u000a on the boundary layer development and turbulent structures in the flow. Detailed two-component laser Doppler velocimetry (LDV)\\u000a and laser-induced fluorescence (LIF) based measurements have been undertaken in regions close to the suction strip and further\\u000a downstream. The region close
Boundary Layer Meteorology (METR 5103)
Droegemeier, Kelvin K.
of the atmospheric boundary layer dynamics and thermodynamics will be taught. Basic concepts of turbulence theory will be discussed and analyzed. Applications of this theory in the atmospheric boundary layer and mesoscale modeling and simulation of turbulent flows in atmospheric boundary layers under different meteorological conditions
5, 31913223, 2005 Boundary layer
Boyer, Edmond
atmospheric research station (53.32 N, 9.90 W) on the west coast of Ireland.25 Boundary layer depthACPD 5, 3191�3223, 2005 Boundary layer structure during NAMBLEX E. G. Norton et al. Title Page Discussions Boundary layer structure and decoupling from synoptic scale flow during NAMBLEX E. G. Norton 1 , G
Boundary Layer Meteorology (METR 5103)
Droegemeier, Kelvin K.
of the atmospheric boundary layer dynamics and thermodynamics, including the basic concepts of turbulence theory conditions will be discussed and critically analyzed. Role of the boundary layer in atmospheric processes be considered. Atmospheric boundary layer types ranging from strongly stable to neutral and to strongly unstable
10, 1990119938, 2010 Boundary layer
Weber, Rodney
ACPD 10, 19901�19938, 2010 Boundary layer dynamics over London J. F. Barlow et al. Title Page (ACP). Please refer to the corresponding final paper in ACP if available. Boundary layer dynamics over Boundary layer dynamics over London J. F. Barlow et al. Title Page Abstract Introduction Conclusions
Spiga, Aymeric
THE MARTIAN ATMOSPHERIC BOUNDARY LAYER A. Petrosyan,1 B. Galperin,2 S. E. Larsen,3 S. R. Lewis,4 A September 2011. [1] The planetary boundary layer (PBL) represents the part of the atmosphere), The Martian atmospheric boundary layer, Rev. Geophys., 49, RG3005, doi:10.1029/2010RG000351. 1. INTRODUCTION
METEOROLOGY 130 Boundary Layer Meteorology
Clements, Craig
is designed to introduce the student to the atmospheric boundary layer and its properties. The course 1. To be able to describe the atmospheric boundary layer conceptually using figures and plots. 2. To understand how measurements of the atmospheric boundary layer are made. Reading and Textbook Roland Stull
Schlieren-based techniques for investigating instability development and transition in a hypersonic boundary layer
NASA Astrophysics Data System (ADS)
Laurence, S. J.; Wagner, A.; Hannemann, K.
Three variants of schlieren techniques are employed to investigate the development of second-mode instability waves in the hypersonic boundary layer of a slender cone in a reflected shock tunnel. First, a previously proposed technique using high frame rate (i.e., at least as high as the dominant instability frequency) schlieren visualization with a continuous light source is shown to provide repeatable measurements of the instability propagation speed and frequency. A modified version of the technique is then introduced whereby a pulsed light source allows the use of a higher-resolution camera with a lower frame rate: this provides significant benefits in terms of spatial resolution and total recording time. A detailed picture of the surface-normal intensity distribution for individual wave packets is obtained, and the images provide comprehensive insight into the unsteady flow structures within the boundary layer. Finally, two-point schlieren deflectometry is implemented and shown to be capable of providing second-mode growth information in the challenging shock tunnel environment.
Spatially Developing Secondary Instabilities and Attachment Line Instability in Supersonic Boundary Layers
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan M.
This paper reports on progress towards developing a spatial stability code for compressible shear flows with two inhomogeneous directions, such as crossflow dominated swept-wing boundary layers and attachment line flows. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined. Finally, extension of the spatial stability analysis to supersonic attachment line flows is also considered.
Coordinated Parameterization Development and Large-Eddy Simulation for Marine and Arctic Cloud-Topped Boundary Layers
NASA Technical Reports Server (NTRS)
Bretherton, Christopher S.
The goal of this project was to compare observations of marine and arctic boundary layers with: (1) parameterization systems used in climate and weather forecast models; and (2) two and three dimensional eddy resolving (LES) models for turbulent fluid flow. Based on this comparison, we hoped to better understand, predict, and parameterize the boundary layer structure and cloud amount, type, and thickness as functions of large scale conditions that are predicted by global climate models. The principal achievements of the project were as follows: (1) Development of a novel boundary layer parameterization for large-scale models that better represents the physical processes in marine boundary layer clouds; and (2) Comparison of column output from the ECMWF global forecast model with observations from the SHEBA experiment. Overall the forecast model did predict most of the major precipitation events and synoptic variability observed over the year of observation of the SHEBA ice camp.
Turbulent boundary layer turbulence intensity similarity formulations
Gary Kunkel; Ivan Marusic
High Reynolds number data obtained in the surface layer of the atmospheric boundary layer at the SLTEST facility are used to analyze and further develop turbulence intensity similarity laws. The analysis of these similarity laws leads to implications concerning the interaction of the inner- and outer-portions of the boundary layer. Namely, the model used to extended formulations across the entire
Study of Boundary Layer Development in a Two-Stage Low-Pressure Turbine
NASA Technical Reports Server (NTRS)
Dorney, Daniel J.; Ashpis, David E.; Halstead, David E.; Wisler, David C.
Experimental data from jet-engine tests have indicated that unsteady blade row (wake) interactions and separation can have a significant impact on the efficiency of turbine stages. The effects of these interactions can be intensified in low-pressure turbine stages because of the low Reynolds number operating environment. Measured turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Thus, during the last decade a significant amount of effort has been put into determining the effects of transition and turbulence on the performance of low pressure turbine stages. Experimental investigations have been performed, for example, by Hodson et al. and Halstead et al. These investigations have helped identify/clarify the roles that factors such as the Reynolds number, free stream turbulence intensity, pressure gradient and curvature have in the generation of losses. In parallel to the experimental investigations, there have been significant analytical efforts to improve the modeling of transition. Examples of such efforts include the works of Mayle and Gostelow et al. These newer models show promise of providing accurate transition predictions over a wide range of flow conditions, although they have yet to be implemented into the numerical flow analyses used by the turbine design community. Some recent computational investigations of interest include the works of Chernobrovkin and Lakshminarayana and Eulitz and Engel. The focus of the current effort has been to -use a viscous, unsteady quasi-three-dimensional Navier-Stokes analysis to study boundary layer development in a two-stage low-pressure turbine. A two-layer algebraic turbulence model, along with a natural transition model and a bubble transition model, have been used, The geometry used in the simulations has been the subject of extensive experiments. The predicted results have been compared with experimental data, including airfoil loadings and time-averaged/unsteady integral boundary layer quantities.
Streamwise development of the wind turbine boundary layer over a model wind turbine array
NASA Astrophysics Data System (ADS)
Newman, Jensen; Lebron, Jose; Meneveau, Charles; Castillo, Luciano
The streamwise development of turbulence statistics and mean kinetic energy in a model wind farm consisting of 3 � 5 wind turbines is studied experimentally in a wind tunnel. The analysis uses planar Particle Image Velocimetry data obtained at the centerline plane of the wind farm, covering the inflow as well as four planes in between five downstream wind turbines. The data analysis is organized by dividing these measurement planes into three regions: the above-rotor, rotor-swept, and below-rotor regions. For each field, flow development is quantified using a properly defined relative difference norm based on an integration over each of the regions. Using this norm, it is found that the mean streamwise velocity approaches a fully developed state most rapidly, whereas the flow development is more gradual for the second-order statistics. The vertical entrainment flux of the mean kinetic energy by the Reynolds shear stress, ?U??u'v'?, is observed to develop at a rate similar to that of the Reynolds shear stress rather than the mean streamwise velocity component. Its development is slowest in the layer nearest to the ground. Analysis of various terms in the mean kinetic energy equation shows that the wind turbine boundary layer has not yet reached fully developed conditions by the fifth turbine but that it is approaching such conditions. By comparing the vertical entrainment flux with the horizontal flux due to the mean flow, it is found that the former increases, whereas the latter decreases, as function of downstream distance, but that the former is already an important contributor in the developing region.
Linking NO2 surface concentration and integrated content in the urban developed atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Dieudonn�, E.; Ravetta, F.; Pelon, J.; Goutail, F.; Pommereau, J.-P.
A statistical linear relationship between NO2 surface concentration and its integrated content in the atmospheric boundary layer (ABL) is established in urban conditions, using ABL depth as an ancillary parameter. This relationship relies on a unique data set including 20 months of observations from a ground-based UV-visible light spectrometer and from an aerosol lidar, both located in Paris inner city center. Measurements show that in all seasons, large vertical gradients of NO2 concentration exist in Paris developed ABL, explaining why the average concentration retrieved is only about 25% of NO2 surface concentration. This result shows that the commonly used hypothesis of constant mixing ratio in the ABL is not valid over urban areas, where large NOx emissions occur. Moreover, the relationship obtained is robust, and the studied area lacks of any particular orographic features, so that our results should be more widely applicable to pollution survey from space-borne observations.
Development of a Multi-Planet Planetary Boundary Layer (PBL) Model
NASA Astrophysics Data System (ADS)
Parimi, V. K.; LeBeau, R. P.; Dowling, T. E.
The planetary boundary layer (PBL) is critical to the atmospheric behavior of any terrestrial planet---as such, there is a plethora of numerical models designed to capture the dynamics of this region. However, many of these models are highly parameterized, relying on data measurements of the planet's atmosphere, typically Earth; such models cannot be reliably applied to other planets without recalibrating for the new environment. This is a challenging task where atmospheric PBL data is rare or non-existent, such as on Venus, Titan, and Triton. In order to reduce the dependence of the PBL model on in situ data, our approach is to draw on recent advances in engineering turbulence research by employing the detached-eddy simulation (DES) concept [Spalart, et. al., 1997]. Our attraction to DES is threefold: it is able to reproduce a variety of benchmark and practical engineering turbulent flows with a high degree of success, it readily fits into eddy viscosity models for turbulence closure, and it transits smoothly from a Reynolds-Averaged Navier-Stokes (RANS) model in the PBL to a Large Eddy Simulation (LES) model aloft, thus providing turbulence closure for the entire atmosphere. We are developing a multi-planet, DES-based PBL model using the EPIC atmospheric model as the platform. The EPIC model is designed to be applicable to all the planetary atmospheres, and therefore requires an accurate, universal boundary layer formulation. We will describe the formulation of a DES-based PBL model within EPIC and present first results obtained for benchmark flows resembling geophysical topography. This work is sponsored by the NASA EPSCoR and Planetary Atmospheres Programs Spalart, P.R., W-H Jou, M. Strelets, and S.R. Allmaras, 1997. ``Comments on the Feasibility of LES for Wings, and on a Hybrid RANS/LES approach'', 1st AFOSR Int. Conference on DNS/LES, in Advances in DNS/LES, C. Liu and Z. Liu (eds), Greyden Press, Columbus, OH.
We present recent experiments and modeling studies of dispersion in the convective boundary layer (CBL) with focus on highly-buoyant plumes that "loft" near the CBL top and resist downward mixing. Such plumes have been a significant problem in earlier dispersion models; they a...
Separation behavior of boundary layers on three-dimensional wings
NASA Technical Reports Server (NTRS)
Stock, H. W.
An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.
Experimental development of the predictive relations for the eddy exchange coefficients for momentum and heat in the atmospheric boundary layer
Jensen, Paul Alfred
' ST EACT. Experir ental Development of thc. Predictive itelacions for the Eddy Exchange Coefficients for iiomentum and Heat in the Atmospheric Houndary Layer. (Deccmb " 1972) PauL Alired Jensen, B. S. , Texas AViS University Directed by: Dr.... '?'illlam H. Clayton Direct measurements of the eddy fluxes of mo. . . entum and heat were. made in the atmospheric boundary layer simultaneously with measurements of the profiles of average wind velocity and tempera- ture to evaluate the capability...
Scaling the atmospheric boundary layer
A. A. M. Holtslag; F. T. M. Nieuwstadt
We review scaling regimes of the idealized Atmospheric Boundary Layer. The main emphasis is given on recent findings for stable conditions. We present diagrams in which the scaling regimes are illustrated as a function of the major boundary-layer parameters. A discussion is given on the different properties of the scaling regimes in unstable and stable conditions.
Study of the development of natural instabilities in a laminar boundary layer in incompressible flow
NASA Technical Reports Server (NTRS)
Burnel, S.; Gougat, P.
Natural instabilities which are created in a laminar boundary layer and which consist of intermittent wave trains were studied. The spectral analysis of these fluctuations makes it possible to localize them in terms of frequency and to isolate their spectrum of amplitude modulation. The variation in terms of abscissa value and ordinate value of these instabilities is compared with the results derived from the solution of the Orr-Sommerfeld equation.
Modeling the urban boundary layer
NASA Technical Reports Server (NTRS)
Bergstrom, R. W., Jr.
A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.
Boundary Layers of Air Adjacent to Cylinders
Nobel, Park S.
Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for ?windd between 200 and 30,000 cm2/second (where ?wind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855
Boundary Layer Control on Airfoils.
ERIC Educational Resources Information Center
Gerhab, George; Eastlake, Charles
A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)
Modelling the transitional boundary layer
NASA Technical Reports Server (NTRS)
Narasimha, R.
Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.
Mean flow development of a longitudinal vortex embedded in an attached, three-dimensional, turbulent boundary layer
Shizawa, T. [Science Univ. of Tokyo (Japan); Eaton, J.K. [Stanford Univ., CA (United States). Dept. of Mechanical Engineering
The interaction of a longitudinal vortex with a pressure-driven, three dimensional turbulent boundary layer was investigated experimentally. The vortex was attenuated much more rapidly in the three dimensional layer than in a two-dimensional boundary layer. The persistence for the vortex-induced perturbation was strongly dependent on the sign of the vortex.
Boundary layers in centrifugal compressors. [application of boundary layer theory to compressor design
NASA Technical Reports Server (NTRS)
Dean, R. C., Jr.
The utility of boundary-layer theory in the design of centrifugal compressors is demonstrated. Boundary-layer development in the diffuser entry region is shown to be important to stage efficiency. The result of an earnest attempt to analyze this boundary layer with the best tools available is displayed. Acceptable prediction accuracy was not achieved. The inaccuracy of boundary-layer analysis in this case would result in stage efficiency prediction as much as four points low. Fluid dynamic reasons for analysis failure are discussed with support from flow data. Empirical correlations used today to circumnavigate the weakness of the theory are illustrated.
Comparisons of rational engineering correlations of thermophoretically-augmented particle mass transfer with STAN5-predictions for developing boundary layers
NASA Technical Reports Server (NTRS)
Gokoglu, S. A.; Rosner, D. E.
Modification of the code STAN5 to properly include thermophoretic mass transport, and examination of selected test cases developing boundary layers which include variable properties, viscous dissipation, transition to turbulence and transpiration cooling. Under conditions representative of current and projected GT operation, local application of St(M)/St(M),o correlations evidently provides accurate and economical engineering design predictions, especially for suspended particles characterized by Schmidt numbers outside of the heavy vapor range.
Hairpin vortices in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Eitel-Amor, G.; �rl�, R.; Schlatter, P.; Flores, O.
The present work presents a number of parallel and spatially developing simulations of boundary layers to address the question of whether hairpin vortices are a dominant feature of near-wall turbulence, and which role they play during transition. In the first part, the parent-offspring regeneration mechanism is investigated in parallel (temporal) simulations of a single hairpin vortex introduced in a mean shear flow corresponding to either turbulent channels or boundary layers (Re? ? 590). The effect of a turbulent background superimposed on the mean flow is considered by using an eddy viscosity computed from resolved simulations. Tracking the vortical structure downstream, it is found that secondary hairpins are only created shortly after initialization, with all rotational structures decaying for later times. For hairpins in a clean (laminar) environment, the decay is relatively slow, while hairpins in weak turbulent environments (10% of ?t) dissipate after a couple of eddy turnover times. In the second part, the role of hairpin vortices in laminar-turbulent transition is studied using simulations of spatial boundary layers tripped by hairpin vortices. These vortices are generated by means of specific volumetric forces representing an ejection event, creating a synthetic turbulent boundary layer initially dominated by hairpin-like vortices. These hairpins are advected towards the wake region of the boundary layer, while a sinusoidal instability of the streaks near the wall results in rapid development of a turbulent boundary layer. For Re? > 400, the boundary layer is fully developed, with no evidence of hairpin vortices reaching into the wall region. The results from both the parallel and spatial simulations strongly suggest that the regeneration process is rather short-lived and may not sustain once a turbulent background is developed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former direct numerical simulation studies is reminiscent of the transitional boundary layer and may not be connected to some aspects of the dynamics of the fully developed wall-bounded turbulence.
Three-dimensional development of the Kelvin-Helmholtz instability in asymmetric boundary layers
NASA Astrophysics Data System (ADS)
Nakamura, T.; Daughton, W. S.; Karimabadi, H.; Eriksson, S.
The Kelvin-Helmholtz instability (KHI) is a key process for the transport of solar wind plasma into the Earth's magnetosphere. In the presence of both magnetic and velocity shear, the resulting KHI leads to generation of vortices and subsequent triggering of magnetic reconnection. Our initial 3D fully kinetic simulations of this process for symmetric boundary layers demonstrated the copious formation of oblique flux ropes, which leads to a chaotic mixing of the plasma within the vortex layer. Here, we consider the effects of density and temperature asymmetries, which are common features across the magnetopause. Past 2D simulations have shown that such asymmetries can lead to an excitation of secondary instabilities along the edge of the vortex in the absence of a finite magnetic field component (B_k) parallel to the k-vector of the KHI. Since B_k is expected to be finite at the magnetopause, here we explore the effect of B_k on secondary instabilities in 3D. We find that the suppression of the secondary instabilities due to B_k is an artifact of the 2D simulations, whereas in 3D the instabilities can grow over a range of oblique angles even when there is a finite B_k. The non-linear growth of these instabilities disturbs the structure of the edge layer of the vortex and further enhances the mixing of the plasma. The implication of these results for transport at the magnetopause will be discussed.
Formaldehyde instrument development and boundary layer sulfuric acid: Implications for photochemistry
NASA Astrophysics Data System (ADS)
Case Hanks, Anne Theresa
This work presents the development of a laser-induced fluorescence technique to measure atmospheric formaldehyde. In conjunction with the technique, the design of a compact, narrow linewidth, etalon-tuned titanium: sapphire laser cavity which is pumped by the second harmonic of a kilohertz Nd:YAG laser is also presented. The fundamental tunable range is from 690-1100 nm depending on mirror reflectivities and optics kit used. The conversion efficiency is at least 25% for the fundamental, and 2-3% for intracavity frequency doubling from 3.5-4W 532 nm pump power. The linewidth is <0.1 cm-1, and the pulsewidth is 18 nsec. Applications of this cavity include the measurement of trace gas species by laser-induced fluorescence, cavity ringdown spectroscopy, and micropulse lidar in the UV-visible region. Also presented are observations of gas-phase sulfuric acid from the NEAQS-ITCT 2K4 (New England Air Quality Study--- Intercontinental Transport and Chemical Transformation) field campaign in July and August 2004. Sulfuric acid values are reported for a polluted environment and possible nucleation events as well as particle growth within the boundary layer are explored. Sulfate production rates via gas phase oxidation of sulfur dioxide are also reported. This analysis allows an important test of our ability to predict sulfuric acid concentration and probe its use as a fast time response photochemical tracer for the hydroxyl radical, OH. In comparison, the NASA time-dependent photochemical box model is used to calculate OH concentration. Nighttime H2SO4 values are examined to test our understanding of nocturnal OH levels and oxidation processes. In comparison, sulfuric acid from a large ground based mission in Tecamac, Mexico (near the northern boundary of Mexico City) during MIRAGE-Mex field campaign (March 2006) is presented. This and other measurements are used to characterize atmospheric oxidation and predict sulfuric acid and OH concentrations at the site. The observations in conjunction with the NASA LARc Photochemical box model are used to explore ozone production, nitrate and sulfate formation, and radical levels and radical production rates during the day. The one minute observations of sulfuric acid, sulfur dioxide, and aerosol surface area were again used to calculate OH levels assuming steady state, and are in good agreement with observations of OH (R2 = 0.7). Photochemical activity is found to be a maximum during the morning hours, as seen in ozone and nitrate formation. Although the model predictions capture the observed diurnal profile, the model underpredicts RO2 concentrations in the morning hours and overpredicts in the afternoon (HO 2 + RO2 radical Model/observed (M/O) � 1.15 and OH M/O � 1.2).
Development of Prototype Micro-Lidar using Narrow Linewidth Semiconductor Lasers for Mars Boundary Layer Wind and Dust Opacity Profiles
NASA Technical Reports Server (NTRS)
Menzies, Robert T.; Cardell, Greg; Chiao, Meng; Esproles, Carlos; Forouhar, Siamak; Hemmati, Hamid; Tratt, David
We have developed a compact Doppler lidar concept which utilizes recent developments in semiconductor diode laser technology in order to be considered suitable for wind and dust opacity profiling in the Mars lower atmosphere from a surface location. The current understanding of the Mars global climate and meteorology is very limited, with only sparse, near-surface data available from the Viking and Mars Pathfinder landers, supplemented by long-range remote sensing of the Martian atmosphere. The in situ measurements from a lander-based Doppler lidar would provide a unique dataset particularly for the boundary layer. The coupling of the radiative properties of the lower atmosphere with the dynamics involves the radiative absorption and scattering effects of the wind-driven dust. Variability in solar irradiance, on diurnal and seasonal time scales, drives vertical mixing and PBL (planetary boundary layer) thickness. The lidar data will also contribute to an understanding of the impact of wind-driven dust on lander and rover operations and lifetime through an improvement in our understanding of Mars climatology. In this paper we discuss the Mars lidar concept, and the development of a laboratory prototype for performance studies, using, local boundary layer and topographic target measurements.
Boundary-layer linear stability theory
NASA Technical Reports Server (NTRS)
Mack, L. M.
Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer reached a stage of development which permit the direct solution of the primary differential equations, numerical results were obtained from the linear theory during the next 10 years for many different boundary layer flows: three dimensional boundary layers; free convention boundary layers; compressible boundary layers; boundary layers on compliant walls; a recomputation of Falkner-Skan flows; unsteady boundary layers; and heated wall boundary layers.
Urban Heat Island Effect and its Impact on Boundary Layer Development and Land-Sea Circulation over Northern Taiwan
NASA Astrophysics Data System (ADS)
Lin, C.; Chen, F.; Huang, J.; Liou, Y.; Chen, W.
The impact of the urban heat island (UHI) effect on environmental phenomena and regional climate has been receiving wide attention in recent decades. Taiwan, especially Taipei (located in northern Taiwan), is experiencing a significant urban heat island effect due to its high population density and the uniqueness of the geographic structure. In order to evaluate the impacts of urbanization and UHI effect over northern Taiwan, a next generation mesoscale model, Weather Research and Forecasting (WRF) model coupled with the Noah land surface model and Urban canopy model (UCM), was used to study this issue. By using the WRF-Noah-UCM model, it has significantly improved our simulation results for the prediction of the UHI effect, boundary layer development, and land sea breeze. Observations of weather stations and Lidar showed that the near surface air temperature was nearly 34 -35�XC and the boundary layer height was nearly 1500 m around noon in Taipei on 17 June 2006. Around midnight, the air temperature ranged from 26 to 28�C. Our model can predict well for boundary layer develop during the daytime and the urban heat island effect in northern Taiwan. Sensitivity tests indicate that the anthropogenic heat (AH) plays an important role for the boundary layer to develop and UHI intensity in the Taipei area, especially during night time and early morning. When we increase AH by 100 W/m2 in the model, the average surface temperature could increase nearly 0.3�C in Taipei. Furthermore, we found the UHI effect also has a significant impact on land sea circulation. It could enhance the sea breeze in the daytime and weaken the land breeze during the night time and thus had a significant impact on the air pollution diffusion in northern Taiwan.
Urban heat island effect and its impact on boundary layer development and land-sea circulation over northern Taiwan
NASA Astrophysics Data System (ADS)
Lin, Chuan-Yao; Chen, Fei; Huang, J. C.; Chen, W.-C.; Liou, Y.-A.; Chen, W.-N.; Liu, Shaw-C.
The impact of the urban heat island (UHI) effect on environmental and regional climate has been receiving wide attention in recent decades. Taiwan, especially Taipei (located in northern Taiwan), is experiencing a significant UHI effect due to its high population density and the uniqueness of the geographic structure. In order to evaluate the impacts of urbanization and UHI effect over northern Taiwan, a next generation mesoscale model, Weather Research and Forecasting (WRF) model coupled with the Noah land surface model and Urban Canopy model (UCM), was used to study this issue. By using the WRF-Noah-UCM model, it has significantly improved our simulation results for the prediction of the UHI effect, boundary layer development, and land sea breeze. Observations of weather stations and Lidar showed that the near surface air temperature was nearly 34-35 �C and the boundary layer height was nearly 1500 m around noon in Taipei on 17 June 2006. Around midnight, the air temperature ranged from 26 to 28 �C. Our model can predict well for boundary layer development during the daytime and the UHI effect in northern Taiwan. Sensitivity tests indicate that the anthropogenic heat (AH) plays an important role for the boundary layer development and UHI intensity in the Taipei area, especially during nighttime and early morning. When we increase AH by 100 W m -2 in the model, the average surface temperature could increase nearly 0.3 �C in Taipei. Furthermore, we found the UHI effect also has a significant impact on land sea circulation. It could enhance the sea breeze in the daytime and weaken the land breeze during the nighttime and hence had a significant impact on the air pollution diffusion in northern Taiwan.
Collaborative Research: ARM observations for the development and evaluation of models and parameterizations of cloudy boundary layers
Albrecht, Bruce,
This is a collaborative project with Dr. Ping Zhu at Florida International University. It was designed to address key issues regarding the treatment of boundary layer cloud processes in climate models with UM�s research focusing on the analyses of ARM cloud radar observations from MMCR and WACR and FIU�s research focusing on numerical simulations of boundary layer clouds. This project capitalized on recent advancements in the ARM Millimeter Cloud Radar (MMCR) processing and the development of the WACR (at the SGP) to provide high temporal and spatial resolution Doppler cloud radar measurements for characterizing in-cloud turbulence, large-eddy circulations, and high resolution cloud structures of direct relevance to high resolution numerical modeling studies. The principal focus of the observational component of this collaborative study during this funding period was on stratocumulus clouds over the SGP site and fair-weather cumuli over the Nauru site. The statistical descriptions of the vertical velocity structures in continental stratocumulus clouds and in the Nauru shallow cumuli that are part of this study represents the most comprehensive observations of the vertical velocities in boundary layer clouds to date and were done in collaboration with Drs. Virendra Ghate and Pavlos Kollias.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.
Nonparallel stability of boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.
The asymptotic formulations of the nonparallel linear stability of incompressible growing boundary layers are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing boundary layers is explained.
Investigation of Mesoscale Variability in Convective Boundary Layer Development Using LASE
NASA Technical Reports Server (NTRS)
Lenschow, Donald H.
Throughout this research effort we have analyzed data collected from the Southern Great Plains 1997 (SGP) experiment to evaluate terms in the budget of water vapor in the atmospheric boundary layer (ABL). The analysis is centered on using data obtained from the Lidar Atmospheric Sensing Experiment (LASE) downward-looking differential absorption lidar (DIAL) that was flown on the NASA-P3 aircraft. The DIAL is able to measure vertical profiles of water vapor, as well as aerosol backscatter, throughout the ABL. Initial work on using the DIAL is summarized in the attached meeting preprint, which discusses results from a segment of the 12 July 1997 flight. Additional analysis has been carried out using both the DIAL data and in situ measurements to obtain more complete and detailed estimates of terms in the ABL water vapor budget. This includes data from the Canadian National Research Council Twin Otter aircraft, as well as from a spectrum of surface-based instruments. This work is expected to lead to a refereed article planned for submission to the Journal.
Boundary Layer Cloudiness Parameterizations Using ARM Observations
Bruce Albrecht
This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.
NASA Astrophysics Data System (ADS)
Coats, D. E.; Berker, D. R.; Dunn, S. S.
This work produced new and better tools for predicting delivered nozzle performance for very high area ratio liquid propellant rocket engines. The motivation for this work is the current interest in space propulsion systems and the high impact that delivered performance has on system design. Design margins can be significantly reduced if the accuracy and reliability of predictive procedures is improved. Two computer programs were developed under this effort. The first of these programs was an extension to the JANNAF standard TDK/BLM code. The second code, called VIPER, was a Parabolized Navier-Stokes solver with finite rate chemistry. An experimental plan to validate the predictive capabilities of the two codes was also formulated. Comparison of both TDK/BLM and VIPER to available data shows excellent agreement.
Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet
NASA Technical Reports Server (NTRS)
Hingst, W. R.; Towne, C. E.
An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.
Asymptotic similarity in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Duncan, Richard D.
The turbulent boundary layer is one of the most fundamental and important applications of fluid mechanics. Despite great practical interest and its direct impact on frictional drag among its many important consequences, no theory absent of significant inference or assumption exists. Numerical simulations and empirical guidance are used to produce models and adequate predictions, but even minor improvements in modeling parameters or physical understanding could translate into significant improvements in the efficiency of aerodynamic and hydrodynamic vehicles. Classically, turbulent boundary layers and fully-developed turbulent channels and pipes are considered members of the same "family," with similar "inner" versus "outer" descriptions. However, recent advances in experiments, simulations, and data processing have questioned this, and, as a result, their fundamental physics. To address a full range of pressure gradient boundary layers, a new approach to the governing equations and physical description of wall-bounded flows is formulated, using a two variable similarity approach and many of the tools of the classical method with slight but significant variations. A new set of similarity requirements for the characteristic scales of the problem is found, and when these requirements are applied to the classical "inner" and "outer" scales, a "similarity map" is developed providing a clear prediction of what flow conditions should result in self-similar forms. An empirical model with a small number of parameters and a form reminiscent of Coles' "wall plus wake" is developed for the streamwise Reynolds stress, and shown to fit experimental and numerical data from a number of turbulent boundary layers as well as other wall-bounded flows. It appears from this model and its scaling using the free-stream velocity that the true asymptotic form of u'2 may not become self-evident until Retheta ? 275,000 or delta+ ? 105, if not higher. A perturbation expansion made possible by the novel inclusion of the scaled streamwise coordinate is used to make an excellent prediction of the shear Reynolds stress in zero pressure gradient boundary layers and channel flows, requiring only a streamwise mean velocity profile and the new similarity map. Extension to other flows is promising, though more information about the normal Reynolds stresses is needed. This expansion is further used to infer a three layer structure in the turbulent boundary layer, and modified two layer structure in fully-developed flows, by using the classical inner and logarithmic profiles to determine which portions of the boundary layer are dominated by viscosity, inertia, or turbulence. A new inner function for U+ is developed, based on the three layer description, providing a much more simplified representative form of the streamwise mean velocity nearest the wall.
A viscous flow study of shock-boundary layer interaction, radial transport, and wake development in a transonic compressor
NASA Technical Reports Server (NTRS)
Hah, Chunill; Reid, Lonnie
A numerical study based on the 3D Reynolds-averaged Navier-Stokes equation has been conducted to investigate the detailed flow physics inside a transonic compressor. 3D shock structure, shock-boundary layer interaction, flow separation, radial mixing, and wake development are all investigated at design and off-design conditions. Experimental data based on laser anemometer measurements are used to assess the overall quality of the numerical solution. An additional experimental study to investigate end-wall flow with a hot-film was conducted, and these results are compared with the numerical results. Detailed comparison with experimental data indicates that the overall features of the 3D shock structure, the shock-boundary layer interaction, and the wake development are all calculated very well in the numerical solution. The numerical results are further analyzed to examine the radial mixing phenomena in the transonic compressor. A thin sheet of particles is injected in the numerical solution upstream of the compressor. The movement of particles is traced with a 3D plotting package. This numerical survey of tracer concentration reveals the fundamental mechanisms of radial transport in this transonic compressor.
Coordinated Parameterization Development and Large-Eddy Simulation for Marine and Arctic Cloud-Topped Boundary Layers
NASA Technical Reports Server (NTRS)
Bretherton, Christopher S.
The goal of this project was to compare observations of marine and arctic boundary layers with (i) parameterization systems used in climate and weather forecast models, and (ii) two and three dimensional eddy resolving (LES) models for turbulent fluid flow. Based on this comparison, we hoped to better understand, predict, and parameterize the boundary layer structure and cloud amount, type and thickness as functions of large scale conditions that are predicted by global climate models.
Controls on boundary layer ventilation: Boundary layer processes and large-scale dynamics
NASA Astrophysics Data System (ADS)
Sinclair, V. A.; Gray, S. L.; Belcher, S. E.
Midlatitude cyclones are important contributors to boundary layer ventilation. However, it is uncertain how efficient such systems are at transporting pollutants out of the boundary layer, and variations between cyclones are unexplained. In this study 15 idealized baroclinic life cycles, with a passive tracer included, are simulated to identify the relative importance of two transport processes: horizontal divergence and convergence within the boundary layer and large-scale advection by the warm conveyor belt. Results show that the amount of ventilation is insensitive to surface drag over a realistic range of values. This indicates that although boundary layer processes are necessary for ventilation they do not control the magnitude of ventilation. A diagnostic for the mass flux out of the boundary layer has been developed to identify the synoptic-scale variables controlling the strength of ascent in the warm conveyor belt. A very high level of correlation (R2 values exceeding 0.98) is found between the diagnostic and the actual mass flux computed from the simulations. This demonstrates that the large-scale dynamics control the amount of ventilation, and the efficiency of midlatitude cyclones to ventilate the boundary layer can be estimated using the new mass flux diagnostic. We conclude that meteorological analyses, such as ERA-40, are sufficient to quantify boundary layer ventilation by the large-scale dynamics.
Performance and boundary-layer evaluation of a sonic inlet
NASA Technical Reports Server (NTRS)
Schmidt, J. F.; Ruggeri, R. S.
Tests were conducted to determine the boundary layer characteristics and aerodynamic performance of a radial vane sonic inlet with a length/diameter ratio of 1 for several vane configurations. The sonic inlet was designed with a slight wavy wall type of diffuser geometry, which permits operation at high inlet Mach numbers (sufficiently high for good noise suppression) without boundary layer flow separation and with good total pressure recovery. A new method for evaluating the turbulent boundary layer was developed to separate the boundary layer from the inviscid core flow, which is characterized by a total pressure variation from hub to tip, and to determine the experimental boundary layer parameters.
Unsteady turbulent boundary layers with flow reversal
NASA Technical Reports Server (NTRS)
Patel, V. C.; Nash, J. F.
A theoretical study is carried out to search for the appearance of a singularity in a family of time-dependent turbulent boundary layers with embedded reverse-flow regions and determine the conditions necessary for its appearance. Further insight is gained into the development of unsteady turbulent boundary layers. The calculations performed for a family of prescribed external velocity distributions in which the relative importance of the effects of time-dependence, compared to those of spatial diffusion, are controlled by a given parameter. The conditions necessary for the appearance of a singularity appears to involve the existence of an appropriate relationship between the dominant velocities in the reversed-flow region and the rate of forward movement of the flow reversal point. The results support the hypothesis that a singularity will exist in the flow if and only if the typical reversed-flow velocities exceed the rate of penetration of the reversed flow into the oncoming boundary layer.
Boundary-layer theory for blast waves
NASA Technical Reports Server (NTRS)
Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.
It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.
Turbulent boundary layer turbulence intensity similarity formulations.
NASA Astrophysics Data System (ADS)
Kunkel, Gary; Marusic, Ivan
High Reynolds number data obtained in the surface layer of the atmospheric boundary layer at the SLTEST facility are used to analyze and further develop turbulence intensity similarity laws. The analysis of these similarity laws leads to implications concerning the interaction of the inner- and outer-portions of the boundary layer. Namely, the model used to extended formulations across the entire turbulent boundary layer suggests the outer portion of the flow does affect the inner portion of the flow. This seems to indicate that turbulence in the near-wall region is not autonomous as suggested by other work. The data were obtained in both `fully' rough and `transitionally' rough boundary layers, and are found to be consistent with the implications of the attached eddy hypothesis as well as Townsend's Reynolds number similarity hypothesis. The latter is in disagreement with recent laboratory studies which suggest roughness does affect the energy-containing motions in the outer portion of the layer. From comparisons with high Reynolds number data, an explanation for this disagreement is given, as are results from new laboratory data.
Measurement of a Mass Transfer Boundary Layer
P. E. Doe
DATA on momentum transfer from velocity measurements are usually applied to mass transfer processes using the accepted analogies between heat, mass and momentum transfer1. Doubts about these analogies, in particular their application to turbulent flow, have led me to develop a method of measuring the wet bulb depression of water vapour in a mass transfer boundary layer formed by water
New evolution equations for turbulent boundary layers
A. E. Perry
Perry, Marusic & Li (1994) (Phys. Fluids, vol. 6(2) part 2) initially developed a mathematical framework for computing the evolution of boundary layers using classical similarity laws such as Prandtl's law of the wall and Coles' law of the wake together with the momentum integral and differential equations. It was found that these equations show that there are 4 parameters
Bursting frequency prediction in turbulent boundary layers
The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.
On the development of a dynamic non-linear closure for large-eddy simulation of the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Lu, Hao; Port�-Agel, Fernando
A dynamic procedure is developed to compute the model coefficients in the recently introduced modulated gradient models for both momentum and scalar fluxes. The magnitudes of the subgrid-scale (SGS) stress and the SGS flux are estimated using the local equilibrium hypothesis, and their structures (relative magnitude of each of the components) are given by the normalized gradient terms, which are derived from the Taylor expansion of the exact SGS stress/flux. Previously, the two model coefficients have been specified on the basis of theoretical arguments. Here, we develop a dynamic SGS procedure, wherein the model coefficients are computed dynamically according to the statistics of the resolved turbulence, rather than provided a priori or ad hoc. Results show that the two dynamically calculated coefficients have median values that are approximately constant throughout the turbulent atmospheric boundary layer (ABL), and their fluctuations follow a near log-normal distribution. These findings are consistent with the fact that, unlike eddy-viscosity/diffusivity models, modulated gradient models have been found to yield satisfactory results even with constant model coefficients. Results from large-eddy simulations of a neutral ABL and a stable ABL using the new closure show good agreement with reference results, including well-established theoretical predictions. For instance, the closure delivers the expected surface-layer similarity profiles and power-law scaling of the power spectra of velocity and scalar fluctuations. Further, the Lagrangian version of the model is tested in the neutral ABL case, and gives satisfactory results.
On the Development of a Dynamic Non-linear Closure for Large-Eddy Simulation of the Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Lu, Hao; Port�-Agel, Fernando
A dynamic procedure is developed to compute the model coefficients in the recently introduced modulated gradient models for both momentum and scalar fluxes. The magnitudes of the subgrid-scale (SGS) stress and the SGS flux are estimated using the local equilibrium hypothesis, and their structures (relative magnitude of each of the components) are given by the normalized gradient terms, which are derived from the Taylor expansion of the exact SGS stress/flux. Previously, the two model coefficients have been specified on the basis of theoretical arguments. Here, we develop a dynamic SGS procedure, wherein the model coefficients are computed dynamically according to the statistics of the resolved turbulence, rather than provided a priori or ad hoc. Results show that the two dynamically calculated coefficients have median values that are approximately constant throughout the turbulent atmospheric boundary layer (ABL), and their fluctuations follow a near log-normal distribution. These findings are consistent with the fact that, unlike eddy-viscosity/diffusivity models, modulated gradient models have been found to yield satisfactory results even with constant model coefficients. Results from large-eddy simulations of a neutral ABL and a stable ABL using the new closure show good agreement with reference results, including well-established theoretical predictions. For instance, the closure delivers the expected surface-layer similarity profiles and power-law scaling of the power spectra of velocity and scalar fluctuations. Further, the Lagrangian version of the model is tested in the neutral ABL case, and gives satisfactory results.
Orbiter Boundary Layer Transition Prediction Tool Enhancements
NASA Technical Reports Server (NTRS)
Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.
Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.
Thick diffusion limit boundary layer test problems
Bailey, T. S. [Lawrence Livermore National Laboratory, 7000 East Avenue, L-095, Livermore, CA 94551 (United States); Warsa, J. S.; Chang, J. H. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87544 (United States); Adams, M. L. [Texas A and M University, Department of Nuclear Engineering, College Station, TX 77843-3133 (United States)
We develop two simple test problems that quantify the behavior of computational transport solutions in the presence of boundary layers that are not resolved by the spatial grid. In particular we study the quantitative effects of 'contamination' terms that, according to previous asymptotic analyses, may have a detrimental effect on the solutions obtained by both discontinuous finite element (DFEM) and characteristic-method (CM) spatial discretizations, at least for boundary layers caused by azimuthally asymmetric incident intensities. Few numerical results have illustrated the effects of this contamination, and none have quantified it to our knowledge. Our test problems use leading-order analytic solutions that should be equal to zero in the problem interior, which means the observed interior solution is the error introduced by the contamination terms. Results from DFEM solutions demonstrate that the contamination terms can cause error propagation into the problem interior for both orthogonal and non-orthogonal grids, and that this error is much worse for non-orthogonal grids. This behavior is consistent with the predictions of previous analyses. We conclude that these boundary layer test problems and their variants are useful tools for the study of errors that are introduced by unresolved boundary layers in diffusive transport problems. (authors)
Turbulent boundary layer behind a separation zone
P. Wauschkuhn; V. I. Vasanta Ram
The turbulent boundary layer after reattachment following separation on a backward-facing step in incompressible flow has been studied experimentally. Hot-wire measurements of the velocity and shear-stress distribution in the boundary layer were made. Furthermore the local wall shear stress was measured by a sub-layer fence. For a considerable distance downstream of reattachment the boundary layer exhibits a region not obeying
Development of a Three-Dimensional PSE Code for Compressible Flows: Stability of Three-Dimensional Compressible Boundary Layers
NASA Technical Reports Server (NTRS)
Balakumar, P.; Jeyasingham, Samarasingham
A program is developed to investigate the linear stability of three-dimensional compressible boundary layer flows over bodies of revolutions. The problem is formulated as a two dimensional (2D) eigenvalue problem incorporating the meanflow variations in the normal and azimuthal directions. Normal mode solutions are sought in the whole plane rather than in a line normal to the wall as is done in the classical one dimensional (1D) stability theory. The stability characteristics of a supersonic boundary layer over a sharp cone with 50 half-angle at 2 degrees angle of attack is investigated. The 1D eigenvalue computations showed that the most amplified disturbances occur around x(sub 2) = 90 degrees and the azimuthal mode number for the most amplified disturbances range between m = -30 to -40. The frequencies of the most amplified waves are smaller in the middle region where the crossflow dominates the instability than the most amplified frequencies near the windward and leeward planes. The 2D eigenvalue computations showed that due to the variations in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the eigenmodes are clustered into isolated confined regions. For some eigenvalues, the eigenfunctions are clustered in two regions. Due to the nonparallel effect in the azimuthal direction, the most amplified disturbances are shifted to 120 degrees compared to 90 degrees for the parallel theory. It is also observed that the nonparallel amplification rates are smaller than that is obtained from the parallel theory.
Diverging boundary layers with zero streamwise pressure gradient
NASA Technical Reports Server (NTRS)
Pauley, Wayne R.; Eaton, John K.; Cutler, Andrew D.
The effects of spanwise divergence on the boundary layer forming between a pair of embedded streamwise vortices with the common flow between them directed toward the wall was studied. Measurements indicate that divergence controls the rate of development of the boundary layer and that large divergence significantly retards boundary layer growth and enhances skin friction. For strongly diverging boundary layers, divergence accounts for nearly all of the local skin friction. Even with divergence, however, the local similarity relationships for two-dimensional boundary layers are satisfactory. Although divergence modifies the mean development of the boundary layer, it does not significantly modify the turbulence structure. In the present experiments with a zero streamwise pressure gradient, it was found that spanwise divergence dit not significantly affect the Reynolds stress and the turbulent triple product distributions.
On Possible Similarity Solutions for Three-Dimensional Incompressible Laminar Boundary-Layer Flows Over Developable Surfaces and with Proportional Mainstream Velocity Components
NASA Technical Reports Server (NTRS)
Hansen, Arthur G.
Analysis is presented on the possible similarity solutions of the three-dimensional, laminar, incompressible, boundary-layer equations referred to orthogonal, curvilinear coordinate systems. Requirements of the existence of similarity solutions are obtained for the following: flow over developable surface and flow over non-developable surfaces with proportional mainstream velocity components.
Students as Simulation Designers and Developers--Using Computer Simulations for Teaching Boundary Layer Processes.
ERIC Educational Resources Information Center
Johnson, Tristan E.; Clayson, Carol Anne
As technology developments seek to improve learning, researchers, developers, and educators seek to understand how technological properties impact performance. This paper delineates how a traditional science course is enhanced through the use of simulation projects directed by the students themselves as a means to increase their level of knowledge�
Atmospheric boundary layer research at Cabauw
A. P. VAN ULDEN; J. Wieringa
At Cabauw, The Netherlands, a 213 m high mast specifically built for meteorological research has been operational since 1973. Its site, construction, instrumentation and observation programs are reviewed. Regarding analysis of the boundary layer at Cabauw, the following subjects are discussed:- terrain roughness;- Monin-Obukhov theory in practice;- the structure of stable boundary layers;- observed evolution of fog layers;- inversion rise
Boundary layer theory and subduction
Fowler, A.C. [Oxford Univ., Oxford (United Kingdom)
Numerical models of thermally activated convective flow in Earth`s mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the `rigid lid` style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth`s mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.
Vortex boundary-layer interactions
NASA Technical Reports Server (NTRS)
Bradshaw, P.
Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.
Progress in modeling hypersonic turbulent boundary layers
NASA Technical Reports Server (NTRS)
Zeman, Otto
A good knowledge of the turbulence structure, wall heat transfer, and friction in turbulent boundary layers (TBL) at high speeds is required for the design of hypersonic air breathing airplanes and reentry space vehicles. This work reports on recent progress in the modeling of high speed TBL flows. The specific research goal described here is the development of a second order closure model for zero pressure gradient TBL's for the range of Mach numbers up to hypersonic speeds with arbitrary wall cooling requirements.
Development of a Ground-Based CO2 Profiling DIAL System for Atmospheric Boundary Layer Studies
NASA Astrophysics Data System (ADS)
Ismail, S.; Davis, K.; Koch, G.; Abedin, M. N.; Refaat, T. F.; Singh, U. N.
NASA Langley Research Center is developing a CO2 profiling Differential Absorption Lidar System operating in the 2.05 micron region. Data from this system can provide vertically resolved CO2 profiles over long continuous observation intervals that can alleviate a primary limit in our ability to derive regional terrestrial CO2 fluxes. Development of this system follows the development of high power, pulsed, narrow bandwidth, tunable lasers with the ability to lock onto optimum absorption lines for the measurement of CO2 profiles. The measurement precision of an existing DIAL system will be enhanced using recently acquired high quantum efficiency, high-gain, and high signal-to-noise ratio detectors and a large collection area telescope. We plan to integrate the ground-based DIAL system and evaluate and optimize its performance before it will be deployed in a field experiments. Well- calibrated, in situ infrared gas analyzers, on the ground and on aircraft, will be used to evaluate the DIAL system. We anticipate that the DIAL system will achieve 1% (3 ppm) absolute accuracy and 0.5% (1.5 ppm) precision while measuring CO2 mixing ratios with 1 km vertical resolution and 30 minute temporal resolution up to range of 4 to 5 km. This system can be used as a validation tool of the OCO (Orbiting Carbon Observatory). Data from the semi-continuous CO2 profiling DIAL system can be used in concert with in situ measurements to enable more precise derivation of regional CO2 fluxes. Examples of CO2 measurements with the existing system will be presented along with the progress made in developing the new system and its projected capability.
Structure of the low latitude boundary layer
NASA Technical Reports Server (NTRS)
Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.
Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.
Boundary layer flow in Trombe wall ducts
NASA Astrophysics Data System (ADS)
Pratt, R.; Karaki, S.
A finite difference material solution technique for the boundary layer equations with an eddy viscosity formulation for turbulence is developed for two-dimensional free convection duct flows. Heat transfer and mass flow rates for air are determined for ducts of uniform but unequal surface temperatures characteristic of Trombe wall ducts. The effect of vents through the wall are modeled as an external pressure drop. Correlations of Nusselt versus Grashof numbers using the duct height as the reference length reduce the heat transfer results for a given vent restriction to a single curve for duct aspect ratios from 10 to 100. Limits to the solution due to the onset of downward flow of air near the cooler surface and the consequent breakdown of the boundary layer assumption are presented.
Entropy production in relativistic jet boundary layers
NASA Astrophysics Data System (ADS)
Kohler, Susanna; Begelman, Mitchell C.
Hot relativistic jets, passing through a background medium with a pressure gradient p ? r-? where 2 < ? ? 8/3, develop a shocked boundary layer containing a significant fraction of the jet power. In previous work, we developed a self-similar description of the boundary layer assuming isentropic flow, but we found that such models respect global energy conservation only for the special case ? = 8/3. Here, we demonstrate that models with ? < 8/3 can be made self-consistent if we relax the assumption of constant specific entropy. Instead, the entropy must increase with increasing r along the boundary layer, presumably due to multiple shocks driven into the flow as it gradually collimates. The increase in specific entropy slows the acceleration rate of the flow and provides a source of internal energy that could be channelled into radiation. We suggest that this process may be important for determining the radiative characteristics of tidal disruption events and gamma-ray bursts from collapsars.
The role of nonlinear critical layers in boundary layer transition
NASA Technical Reports Server (NTRS)
Goldstein, M.E.
Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.
Boundary Layer Transition Results From STS-114
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Cassady, Amy M.; Kirk, Benjamin S.; Wang, K. C.; Hyatt, Andrew J.
The tool for predicting the onset of boundary layer transition from damage to and/or repair of the thermal protection system developed in support of Shuttle Return to Flight is compared to the STS-114 flight results. The Boundary Layer Transition (BLT) Tool is part of a suite of tools that analyze the aerothermodynamic environment of the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time of transition onset is predicted to help determine the proper aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against flight data. Computed local boundary layer edge conditions provided the means to correlate the experimental results and then to extrapolate to flight. During STS-114, the BLT Tool was utilized and was part of the decision making process to perform an extravehicular activity to remove the large gap fillers. The role of the BLT Tool during this mission, along with the supporting information that was acquired for the on-orbit analysis, is reviewed. Once the large gap fillers were removed, all remaining damage sites were cleared for reentry as is. Post-flight analysis of the transition onset time revealed excellent agreement with BLT Tool predictions.
Boundary layers of the earth's outer magnetosphere
NASA Technical Reports Server (NTRS)
Eastman, T. E.; Frank, L. A.
The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.
Overview of the GEWEX Atmospheric Boundary Layer Study (GABLS)
A. A. M. Holtslag; G. Svensson; S. Basu; B. Beare; F. C. Bosveld; J. Cuxart
In 2001 the steering group of GEWEX (formally known as the Global Energy and Water Cycle Experiment) initiated the GEWEX Atmospheric Boundary Layer Study (GABLS). The objective of GABLS is to improve the representation of the atmospheric boundary layer in regional and large-scale atmospheric models. As such, GABLS provides a platform for model inter-comparison and development to benefit studies of
Boundary layer development as a function of chamber pressure in the NASA Lewis 1030:1 area ratio rocket nozzle
NASA Technical Reports Server (NTRS)
Smith, Tamara A.
Through the use of theoretical predictions of fluid properties and experimental heat transfer and thrust measurements, the zones of laminar, transitional, and turbulent boundary layer flow were defined for the NASA Lewis 1030:1 area ratio rocket nozzle. Tests were performed on the nozzle at chamber pressures from 350 to 100 psia. For these conditions, the throat diameter Reynolds numbers varied from 300,000 to 1 million. The propellants used were gaseous hydrogen and gaseous oxygen. Thrust measurements and nozzle outer wall temperature measurements were taken during the 3-sec test runs. Comparison of experimental heat transfer and thrust data with the corresponding predictions from the Two-Dimensional Kinetics (TDK) nozzle analysis program indicated laminar flow in the nozzle at a throat diameter Reynolds number of 320,000 or chamber pressure of 360 psia. Comparison of experimental and predicted heat transfer data indicated transitional flow up to and including a chamber pressure of 1000 psia. Predicted values of the axisymmetric acceleration parameter within the convergent and divergent nozzle were consistent with the above results. Based upon an extrapolation of the heat transfer data and predicted distributions of the axisymmetric acceleration parameter, transitional flow was predicted up to a throat diameter Reynolds number of 220,000 or 2600-psia chamber pressure. Above 2600-psia chamber pressure, fully developed turbulent flow was predicted.
Hypersonic Boundary Layer/Oblique Shockwave Interaction
NASA Astrophysics Data System (ADS)
Lindsay, Haile
The hypersonic boundary layer/oblique shockwave interaction problem was defined with the use of the full Navier-Stokes (NS) equations and a FORTRAN code was developed to provide numerical solutions to this problem. Further, this problem was studied under two specified sets of boundary conditions: adiabatic wall and constant wall conditions. The MacCormack Technique was used in developing this NS code. To validate the numerical code, the flat plate problem was solved, and the results compared to that published in established journals. In solving these problems, engineering tools such as, FORTRAN, TECPLOT, and EXCEL, were used to generate plots of the primitive variables, such as, the velocity components, u and v, density, and the temperature T. Selected plots were reproduced from various references in validating the work done for the flat plate and hypersonic boundary layer/oblique shockwave interaction problems. All preliminary results indicated that the code was validated and the results obtained agreed with the physical behavior of the flow fields. Now that an aerospace engineering tool was developed, it is recommended that future designers seek to further its development by making the code user-friendly and that they further test accuracy of the code by solving other 2D fluid dynamic problems.
Cyclone separator having boundary layer turbulence control
Krishna, Coimbatore R. (Mt. Sinai, NY); Milau, Julius S. (Port Jefferson, NY)
A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.
Turbulence structure in a hypersonic boundary layer
NASA Astrophysics Data System (ADS)
Baumgartner, Mark Lawrence
This dissertation provides new insights into the structure of compressible turbulent boundary layers in the hypersonic regime. Previous studies of compressible turbulent boundary layers have indicated that subtle differences may exist between subsonic and supersonic layers with respect to their structure angles, length scales, and intermittency functions. It was believed that a study at hypersonic speeds would provide information on characteristic differences attributable to Mach number effects. Towards this goal, a Mach 8 wind tunnel with a 9' axisymmetric test section was built at the Gas Dynamics Laboratory at Princeton University. The Mach 8 facility can produce flows with stagnation temperatures up to 1050 F (840 K) and stagnation pressures up to 1300 psi (9 MPa). Unit Reynolds numbers obtainable in the facility range from 3�106/m to 20�106/m. The focus of this dissertation is the zero-pressure- gradient hypersonic turbulent boundary layer on a flat plate. Mean pitot pressure and stagnation temperature surveys of the boundary layer at a Reynolds number Re/sb/theta/approx 3600 under moderately cold wall boundary conditions were performed and compared with theoretical predictions and previous experiments. Cross-sectional images of a hypersonic turbulent boundary layer were produced using filtered Rayleigh scattering to study the instantaneous structure of the boundary layer (previous visualizations of hypersonic boundary layers have relied on shadow-graph or schlieren techniques). The resulting images provided qualitative and quantitative information about turbulent structure which were then compared with those of sub- and supersonic data.
Numerical simulation of a controlled boundary layer
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Hussaini, M. Yousuff
The problem of interest is the boundary layer over a flat plate. The three standard laminar flow control (LFC) techniques are pressure gradient, suction, and heating. The parameters used to describe the amount of control in the context of the boundary layer equations are introduced. The numerical method required to find the mean flow, the linear eigenvalues of the Orr-Sommerfeld equation, and the full, nonlinear, 3-D solution of the Navier-Stokes equations are outlined. A secondary instability exists for the parallel boundary subject to uniform pressure gradient, suction, or heating. Selective control of the spanwise mode reduces the secondary instability in the parallel boundary layer at low Reynolds number.
On an Asymptotically Consistent Unsteady Interacting Boundary Layer
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.
LDV measurements of turbulent baroclinic boundary layers
Neuwald, P.; Reichenbach, H. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany); Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States)
Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.
The development of models for boundary layers with usage of nonlinear dynamics methods based on matrix decomposition
NASA Astrophysics Data System (ADS)
Minervina, H.; Krot, A.; Tkachova, P.
This work is devoted to computer modeling of aerodynamic flows into the boundary layers [1] with usage of nonlinear dynamics methods including the matrix decomposition method in the state-space [2] and the fractal- topological methods [3]. The computer simulation of air flows is carried out by means of program package STAR-CD [4].The computer modeling based on STAR-CD includes the realization of the procedures for import of CAD 3D-geometry of the treated surfaces into the instrumental tool of Pro*am STAR-CD, the treatment of the imported surfaces and generation of new surface, variable subsurface thickness and volume meshes with the usage of the tool of Pro*am STAR-CD, the computing aerodynamic flows into the boundary layers based on STAR-CD [4]. The obtained vector field of velocities as well as the scalar field of mass density and the distribution of pressure into the boundary layers are analysed then as depending on initial and boundary conditions. According to the first approach, the obtained time series of the component velocity, mass density and pressure are proceed into the pseudo-phase space.The reconstructed attractors are investigated by means of estimations of their fractal-topological characterictics (the minimal attractor embedding dimension, Lyapunov exponents, etc.). According to the second approach, the system of partial differential equations of Prandtl and Karman (describing aerodynamic processes in the boundary layers) is reduced to the system of ordinary differential equations based on the Galerkin's method.Then the fractal-topological characterictics of attractor of this system are investigated.The obtained results of analysis in accord with the first and the second approaches are compared with each other. References: [1] H. Schlichting, Grenzschicht-Theorie. Verlag G Braun, Karlsruhe, 1970. [2] A.M. Krot, "Matrix decompositions of vector functions and shift operators on the trajectories of a nonlinear dynamical system", Nonlinear Phenomena in Complex Systems, vol. 4, N2, 2001, pp. 106-115. [3] A.M. Krot and H.B. Minervina "Minimal attractor embedding estimation based on matrix decomposition for analysis of dynamical systems", Nonlinear Phenomena in Complex Systems, vol.5, N2, 2002, pp.161-172. [4] Methodology for STAR-CD: Version 3.15A ((c)2002 Computational Dynamics Limited).
Unsteadiness of Shock Wave / Boundary Layer Interactions
NASA Astrophysics Data System (ADS)
Clemens, Noel
Shock wave / boundary layer interactions are an important feature of high-speed flows that occur in a wide range of practical configurations including aircraft control surfaces, inlets, missile base flows, nozzles, and rotating machinery. These interactions are often associated with severe boundary layer separation, which is highly unsteady, and exhibits high fluctuating pressure and heat loads. The unsteady motions are characterized by a wide range of frequencies, including low-frequency motions that are about two orders of magnitude lower than those that characterize the upstream boundary layer. It is these low-frequency motions that are of most interest because they have been the most difficult to explain and model. Despite significant work over the past few decades, the source of the low-frequency motions remains a topic of intense debate. Owing to a flurry of activity over the past decade on this single topic we are close to developing a comprehensive understanding of the low-frequency unsteadiness. For example, recent work in our laboratory and others suggests that the driving mechanism is related to low-frequency fluctuations in the upstream boundary layer. However, several recent studies suggest the dominant mechanism is an intrinsic instability of the separated flow. Here we attempt to reconcile these views by arguing that the low-frequency unsteadiness is driven by both upstream and downstream processes, but the relative importance of each mechanism depends on the strength (or length-scale) of separation. In cases where the separation bubble is relatively small, then the flow is intermittently separated, and there exists a strong correlation between upstream velocity fluctuations and the separation bubble dynamics. It appears that superstructures in the upstream boundary layer can play an important role in driving the unsteadiness for this case. It is not clear, however, if the upstream fluctuations directly move the separation point or indirectly couple to a global instability. In cases where the separation is strong (and the bubble large) then the bubble pulsates owing to a global instability, as has been suggested by other researchers. In this case upstream turbulence may serve mainly as a source of broadband fluctuations that seed the large-scale instability of the separated flow.
Planetary Boundary Layer Simulation Using TASS
NASA Technical Reports Server (NTRS)
Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael
Boundary conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the atmospheric boundary layer. Several options are now available, including the use of a surface energy balance. In addition, we compare convective boundary layer simulations with the Wangara and Minnesota field experiments as well as with other model results. We find excellent agreement of modelled mean profiles of wind and temperature with observations and good agreement for velocity variances. Neutral boundary simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.
Energy transport using natural convection boundary layers
Anderson, R.
Natural convection is one of the major modes of energy transport in passive solar buildings. There are two primary mechanisms for natural convection heat transport through an aperture between building zones: (1) bulk density differences created by temperature differences between zones; and (2) thermosyphon pumping created by natural convection boundary layers. The primary objective of the present study is to compare the characteristics of bulk density driven and boundary layer driven flow, and discuss some of the advantages associated with the use of natural convection boundary layers to transport energy in solar building applications.
Boundary layers on longitudinally grooved walls (riblets)
NASA Astrophysics Data System (ADS)
Fulachier, L.; Djenidi, L.; Anselmet, F.
The boundary layer of riblets has been investigated in a hydrodynamic wind tunnel. For the case of triangularly grooved riblets, laser velocimetry visualizations show flow stabilization to occur for a turbulent boundary layer, and a decreased longitudinal velocity profile slope and a rapid relaxation downstream to occur for a laminar boundary layer. U-shaped grooves are found to have no effect. Visualizations of triangularly gooved riblets of several dimensions indicate that no counterrotating vortices exist in the grooves. This result is confirmed by profiles of the longitudinal velocity component, which show an increase in the velocity gradient near the crest and a significant decrease in the groove.
Dynamic Acoustic Detection of Boundary Layer transition
NASA Technical Reports Server (NTRS)
Grohs, Jonathan R.
The wind tunnel investigation into the acoustic nature of boundary layer transition using miniature microphones. This research is the groundwork for entry into the National Transonic Facility (NTF) at the NASA Langley Research Center (LaRC). Due to the extreme environmental conditions of NTF testing, low temperatures and high pressures, traditional boundary layer detection methods are not available. The emphasis of this project and further studies is acoustical sampling of a typical boundary layer and environmental durability of the miniature microphones. The research was conducted with the 14 by 22 Foot Subsonic Tunnel, concurrent with another wind tunnel test. Using the resources of LaRC, a full inquiry into the feasibility of using Knowles Electronics, Inc. EM-3086 microphones to detect the surface boundary layer, under differing conditions, was completed. This report shall discuss the difficulties encountered, product performance and observations, and future research adaptability of this method.
Propulsion via buoyancy driven boundary layer
Doyle, Brian Patrick
Heating a sloped surface generates a well-studied boundary layer flow, but the resulting surface forces have never been studied in propulsion applications. We built a triangular wedge to test this effect by mounting a ...
Boundary layer flow visualization for flight testing
NASA Technical Reports Server (NTRS)
Obara, Clifford J.
Flow visualization is used extensively in flight testing to determine aerodynamic characteristics such as surface flow direction and boundary layer state. Several visualization techniques are available to the aerodynamicist. Two of the most popular are oil flows and sublimating chemicals. Oil is used to visualize boundary layer transition, shock wave location, regions of separated flow, and surface flow direction. Boundary layer transition can also be visualized with sublimating chemicals. A summary of these two techniques is discussed, and the use of sublimating chemicals is examined in some detail. The different modes of boundary layer transition are characterized by different patterns in the sublimating chemical coating. The discussion includes interpretation of these chemical patterns and the temperature and velocity operating limitations of the chemical substances. Information for selection of appropriate chemicals for a desired set of flight conditions is provided.
Large Eddy Simulation of Atmospheric Convective Boundary Layer with Realistic
Fedorovich, Evgeni
Large Eddy Simulation of Atmospheric Convective Boundary Layer with Realistic Environmental atmospheric environmental forcings. Analysis of several simulated convec- tive boundary layer (CBL) cases toward dynamic adjustment of environmental parameters in LES of atmospheric boundary layer flows
Boundary-layer stability and airfoil design
NASA Technical Reports Server (NTRS)
Viken, Jeffrey K.
Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.
Thunderstorm influence on boundary layer winds
Schmidt, Jill Marie
THUNDERSTORM INFLUENCE ON BOUNDARY LAYER WINDS A Thesis by JILL MARIE SCHMIDT Submitted to the Graduate College of Texas ASM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1986 Major... Subject: Meteorology THUNDERSTORM INFLUENCE ON BOUNDARY LAYER WINDS A Thesis by JILL MARIE SCHMIDT Approved as to style and content by: James R. Scog s (Chairman of Committee) Kenneth C. Brundidge (Member) Qmer . Jenklns (Member) James R...
Two-fluid boundary layer stability
G. Degrez; G. S. R. Sarma
The stability of a two-fluid boundary layer is investigated. A boundary layer shears a second fluid that is bounded by the wall and the shearing fluid. The eigenvalue problem governing the linear stability of the configuration is solved using an efficient shooting-search method. Besides the Tollmien-Schlichting mode (hard mode) found in the classical hydrodynamical stability theory an additional Yih-mode (interfacial
Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models
NASA Technical Reports Server (NTRS)
Eastman, Timothy E.
Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key theoretical issues have been discussed for over two decades. This is because plasma instruments deployed prior to the ISEE and AMPTE missions did not have the required time resolution and most ISEE investigations to-date have focused on tests of MHD plasma models, especially reconnection. More recently, many phenomenological and theoretical models have been developed to explain the existence and characteristics of the magnetospheric boundary layers with only limited success to date. The cases with no boundary layer treated in this study provide a contrary set of conditions to those observed with a boundary layer. For the measured parameters of such cases, a successful boundary layer model should predict no plasma penetration across the magnetopause. Thus, this research project provides the first direct observational tests of magnetopause models using pristine magnetopause crossings and provides important new results on magnetopause microstructure and associated kinetic processes.
Observational Study of the Atmospheric Boundary Layer over Antarctica
Zbigniew Sorbjan; Yuji Kodama; Gerd Wendler
During the austral summer of 1982\\/83, measurements of wind and temperature profiles were made through the atmospheric boundary layer in Adelie Land, East Antarctica, an area known for strong katabatic winds. It was found that a shallow but strong temperature inversion was developed at night, and destroyed during the day, resulting in the development of a well-mixed layer. Wind hodographs
Boundary-layer predictions for small low-speed contractions
NASA Technical Reports Server (NTRS)
Mehta, Rabindra D.; Bell, James H.
The present scheme for the prediction of boundary-layer development in small, low-speed wind tunnel contraction sections proceeds by calculating the wall pressure distributions, and hence the wall velocity distributions, by means of a three-dimensional potential-flow method. For the family of contractions presently treated, the assumption of a laminar boundary layer appears to be justified; the measured boundary layer momentum thicknesses at the exit of the four contractions were found to lie within 10 percent of predicted values.
The passive control of compressible boundary layer growth by boundary layer trips
NASA Technical Reports Server (NTRS)
Chou, J. H.; Childs, M. E.
The passive control of compressible boundary layer growth by boundary layer trips has been studied experimentally. Axisymmetric trips and three dimensional trips were used in this study. The nomial freestream Mach numbers are 1.5 and 4. The results show that trips are effective in promoting boundary layer growth. Trips are more effective for Mach 1.5 flows than for Mach 4 flows.
Calculations of unsteady turbulent boundary layers with flow reversal
NASA Technical Reports Server (NTRS)
Nash, J. F.; Patel, V. C.
The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.
On similarity in the atmospheric boundary layer
Zbigniew Sorbjan
A similarity theory for the atmospheric boundary layer is presented. The Monin-Obukhov similarity theory for the surface layer is a particular case of this new theory, for the case of z ? 0. Universal functions which are in agreement with empirical data are obtained for the stable and convective regimes.
Ground observations of magnetospheric boundary layer phenomena
McHenry, M.A.; Clauer, C.R. (Stanford Univ., CA (USA)); Friis-Christensen, E. (Danish Meteorological Inst., Copenhagen (Denmark)); Newell, P.T. (Johns Hopkins Univ., Laurel, MD (USA)); Kelly, J.D. (SRI International, Menlo Park, CA (USA))
Several classes of traveling vortices in the dayside ionospheric convection have been detected and tracked using the Greenland magnetometer chain (Friis-Christensen et al., 1988, McHenry et al., 1989). One class observed during quiet times consists of a continuous series of vortices moving generally anti-sunward for several hours at a time. The vortices strength is seen to be approximately steady and neighboring vortices rotate in opposite directions. Sondrestrom radar observations show that the vortices are located at the ionospheric convection reversal boundary. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, the authors argue that this class of vortices is caused by the Kelvin-Helmholtz instability of the inner edge of the magnetospheric boundary layer.
Lear jet boundary layer/shear layer laser propagation experiments
NASA Astrophysics Data System (ADS)
Gilbert, K.
Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.
Lear jet boundary layer/shear layer laser propagation experiments
NASA Technical Reports Server (NTRS)
Gilbert, K.
Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.
High enthalpy hypersonic boundary layer flow
NASA Technical Reports Server (NTRS)
Yanow, G.
A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.
The kinematics of turbulent boundary layer structure
NASA Technical Reports Server (NTRS)
Robinson, Stephen Kern
The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.
Coherent Motions of the Turbulent Boundary Layer (Invited)
NASA Astrophysics Data System (ADS)
Adrian, R. J.
Over the last decade a model has been developed in which the structure of the turbulent boundary consists of quasi-streamwise vortices near the wall, a hierarchy of hairpin vortex packets that extends through the logarithmic layer, large-scale motions having streamwise extent of the order of the thickness of the boundary layer, and very-large-scale motions that are much longer than the boundary layer thickness. Figure 1 shows a cartoon sketch of the hairpin packet hierarchy. The evidence indicates that the large and very-large-scale motions become increasingly important as the Reynolds number increases, implying that geophysical boundary layer have considerably different character than low Reynolds number laboratory experiments and simulations. Work is in progress to discern the form of the large motions and incorporate them into a more complete model. Fig. 1. Hierarchy of hairpin packets begins at the surface.
Simulating supercell thunderstorms in a convective boundary layer: Effects on storm and boundary layer properties
NASA Astrophysics Data System (ADS)
Nowotarski, Christopher J.
Nearly all previous numerical simulations of supercell thunderstorms have neglected surface uxes of heat, moisture, and momentum as well as horizontal inhomogeneities in the near-storm environment from resulting dry boundary layer convection. This investigation uses coupled radiation and land-surface schemes within an idealized cloud model to identify the effects of organized boundary layer convection in the form of horizontal convective rolls (HCRs) on the strength, structure, and evolution of simulated supercell thunderstorms. The in uence of HCRs and the importance of their orientation relative to storm motion is tested by comparing simulations with a convective boundary layer (CBL) against those with a horizontally homogeneous base state having the same mean environment. The impact of anvil shading on the CBL is tested by comparing simulations with and without the effects of clouds in the radiative transfer scheme. The results of these simulations indicate that HCRs provide a potentially important source of environmental vertical vorticity in the sheared, near-storm boundary layer. These vorticity perturbations are amplified both beneath the main supercell updraft and along the trailing out ow boundary, leading to the formation of occasionally intense misovortices. HCRs perpendicular to storm motion are found to have a detrimental effect on the strength and persistence of the lowlevel mesocyclone, particularly during its initial development. Though the mean environment is less supportive of low-level rotation with a wind profile conducive to HCRs oriented parallel to storm motion, such HCRs are found to often enhance the low-level mesocyclone circulation. When anvil shading is included, stabilization results in generally weaker low-level mesocyclone circulation, regardless of HCR orientation. Moreover, HCRs diminish in the near-storm environment such that the effects of HCRs on the supercell are mitigated. HCRs are also shown to be a necessary condition for the formation of so-called "feeder clouds" and anking line convection in these simulations. These findings suggest potentially important rami fications regarding both non-mesocyclone and mesocyclone tornadoes in supercell thunderstorms in an environment with active boundary layer convection.
Boundary-layer depth and entrainment zone characterization with a boundary-layer profiler
Wayne M. Angevine; Allen B. White; S. K. Avery
A technique for determining the height of the convective atmospheric boundary layer (CBL) with a 915 MHz boundary-layer profiler is discussed. The results are compared with CBL heights determined from radiosonde measurements. The profiler provides continuous CBL height measurements with very good time resolution (30 minutes or less), allowing for detailed understanding of the growth and fluctuations of the CBL.
Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow
NASA Technical Reports Server (NTRS)
Mack, L. M.
The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.
Calculation methods for compressible turbulent boundary layers, 1976
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.
Boundary-Layer Meteorology An International Journal of Physical,
Marusic, Ivan
Processes in the Atmospheric Boundary Layer ISSN 0006-8314 Volume 147 Number 1 Boundary-Layer Meteorol (20131 23 Boundary-Layer Meteorology An International Journal of Physical, Chemical and Biological after publication. #12;Boundary-Layer Meteorol (2013) 147:41�50 DOI 10.1007/s10546-012-9777-7 ARTICLE
Bordoni, Simona
of clouds and atmospheric boundary layers, from a phenomenological overview of cloud and boundary layer) � The Atmospheric Boundary Layer, J. R. Garratt (Cambridge UP, 1992) � Turbulence in the Atmosphere, J. C. WyngaardESE 134: BOUNDARY LAYER AND CLOUD DYNAMICS - SPRING 2013 SYLLABUS Introduction to the dynamics
Improved Boundary Layer Depth Retrievals from MPLNET
NASA Technical Reports Server (NTRS)
Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette
Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, MD since April 2001. However, because of issues with the operational PBL depth algorithm, the data is not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers, and in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System-version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by 410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they diered the most in the winter.
Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation
Reichenbach, H.; Neuwald, P. [Ernst-Mach-Institut, Freiburg (DE); Kuhl, A.L. [R and D Associates, Los Angeles, CA (United States)
This technical report describes methods that were applied to investigate turbulent boundary layers generated by inviscid, baroclinic effects. The Cranz-Schardin 24-sparks camera was used to visualize the interactions of a planar shock wave with a Freon R12-layer. The shock propagates more slowly in the Freon layer than in air because of its smaller sound speed. This causes the shock front to be curved and to be reflected between the wall and the layer interface. As a consequence of the reflection process, a series of compression and expansion waves radiate from the layer. Large fluctuations in the streamwise velocity and in pressure develop for about 1 ms. These waves strongly perturb the interface shear layer, which rapidly transitions to a turbulent boundary flow. Pressure measurements showed that the fluctuations in the Freon layer reach a peak pressure 4 times higher than in the turbulent boundary flow. To characterize the preshock Freon boundary layer, concentration measurements were performed with a differential interferometry technique. The refraction index of Freon R12 is so high that Mach-Zehnder interferometry was not successful in these experiments. The evaluation of the concentration profile is described here in detail. Method and results of corresponding LDV measurements under the same conditions are presented in a different report, EMI Report T 9/92. The authors plan to continue the dense gas layer investigations with the gas combination helium/Freon.
Soot and radiation in combusting boundary layers
Beier, R.A.
In most fires thermal radiation is the dominant mode of heat transfer. Carbon particles within the fire are responsible for most of this emitted radiation and hence warrant quantification. As a first step toward understanding thermal radiation in full scale fires, an experimental and theoretical study is presented for a laminar combusting boundary layer. Carbon particulate volume fraction profiles and approximate particle size distributions are experimentally determined in both free and forced flow for several hydrocarbon fuels and PMMA (polymethylmethacrylate). A multiwavelength laser transmission technique determines a most probable radius and a total particle concentration which are two unknown parameters in an assumed Gauss size distribution. A sooting region is observed on the fuel rich side of the main reaction zone. For free flow, all the flames are in air, but the free stream ambient oxygen mass fraction is a variable in forced flow. To study the effects of radiation heat transfer, a model is developed for a laminar combusting boundary layer over a pyrolyzing fuel surface. An optically thin approximation simplifies the calculation of the radiant energy flux at the fuel surface. For the free flames in air, the liquid fuel soot volume fractions, f/sub v/, range from f/sub v/ approx. 10/sup -7/ for n-heptane, a paraffin, to f/sub v/ approx. 10/sup -7/ for toluene, an aromatic. The PMMA soot volume fractions, f/sub v/ approx. 5 x 10/sup -7/, are approximately the same as the values previously reported for pool fires. Soot volume fraction increases monotonically with ambient oxygen mass fraction in the forced flow flames. For all fuels tested, a most probable radius between 20 nm and 80 nm is obtained which varies only slightly with oxygen mass fraction, streamwise position, or distance normal to the fuel surface. The theoretical analysis yields nine dimensionless parameters, which control the mass flux rate at the pyrolyzing fuel surface.
New evolution equations for turbulent boundary layers
NASA Astrophysics Data System (ADS)
Perry, A. E.
Perry, Marusic & Li (1994) (Phys. Fluids, vol. 6(2) part 2) initially developed a mathematical framework for computing the evolution of boundary layers using classical similarity laws such as Prandtl's law of the wall and Coles' law of the wake together with the momentum integral and differential equations. It was found that these equations show that there are 4 parameters which control the streamwise evolution of the layer and the Reynolds shear stress distribution and these are S, ?, ? and ?. S = U_1/U_?, ? is Coles wake factor, ? is the Clauser pressure gradient parameter and ?=S?_cd?/dx. In this early work the evolution equations were incomplete and the only problems which could be solved were the so called quasi-equilibrium flow cases where it could be assumed that ? was sufficiently small to neglect its effect. Here we present the full set of evolution equations for finite ? so that the more general problem of non-equilibrium layers can be tackled. In this initial study here, closure is obtained assuming that \\calF[S, ?, ?, ?] = 0 and this function is mapped out semi-empirically. The formulation is consistent with the recently extended attached eddy hypothesis of Perry & Marusic (1995) (JFM vol. 298) from which once the mean flow evolution has been calculated, the broadband turbulence intensities and spectra can be calculated. The use of topology as a diagnostic tool to interpret DNS data tends to support this recently developed hypothesis (Chong et al. 1998) (JFM vol. 357) and preliminary modeling is carried out in conjunction with these evolution equations so as to obtain closure based on physical arguments. Some nonequilibrium flow data is compared with computations using these new evolution equations.
Application of a Reynolds stress model to separating boundary layers
NASA Technical Reports Server (NTRS)
Ko, Sung HO
Separating turbulent boundary layers occur in many practical engineering applications. Nonetheless, the physics of separation/reattachment of flows is poorly understood. During the past decade, various turbulence models were proposed and their ability to successfully predict some types of flows was shown. However. prediction of separating/reattaching flows is still a formidable task for model developers. The present study is concerned with the process of separation from a smooth surface. Features of turbulent separating boundary layers that are relevant to modeling include the following: the occurrence of zero wall shear stress, which causes breakdown of the boundary layer approximation; the law of the wall not being satisfied in the mean back flow region; high turbulence levels in the separated region; a significant low-frequency motion in the separation bubble; and the turbulence structure of the separated shear layer being quite different from that of either the mixing layers or the boundary layers. These special characteristics of separating boundary layers make it difficult for simple turbulence models to correctly predict their behavior.
Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...
A simple model of the atmospheric boundary layer; sensitivity to surface evaporation
I B Troen; L. Mahrt
A simple formulation of the boundary layer is developed for use in large-scale models and other situations where simplicity is required. The formulation is suited for use in models where some resolution is possible within the boundary layer, but where the resolution is insufficient for resolving the detailed boundary-layer structure and overlying capping inversion. Surface fluxes are represented in terms
Coupling of magnetopause-boundary layer to the polar ionosphere
NASA Technical Reports Server (NTRS)
Wei, C. Q.; Lee, L. C.
The plasma dynamics in the low-latitude boundary layer and its coupling to the polar ionosphere under boundary conditions at the magnetopause are investigated. In the presence of a driven plasma flow along the magnetopause, the Kelvin-Helmholtz instability can develop, leading to the formation and growth of plasma vortices in the boundary layer. The finite ionospheric conductivity leads to the decay of these vortices. The competing effect of the formation and decay of vortices leads to the formation of strong vortices only in a limited region. Several enhanced field-aligned power density regions associated with the boundary layer vortices and the upward field-aligned current (FAC) filaments can be found along the postnoon auroral oval. These enhanced field-aligned power density regions may account for the observed auroral bright spots.
Goertler instability of a hypersonic boundary layer
L. de Luca; G. Cardone; D. Aymer de la Chevalerie; A. Fonteneau
The Goertler instability of a hypersonic boundary layer and its influence on the wall heat transfer are experimentally analyzed. Measurements, made in a wind tunnel by means of a computerized infrared (IR) imaging system, refer to the flow over two-dimensional concave walls. Wall temperature maps (that are interpreted as surface flow visualizations) and spanwise heat transfer fluctuations are presented. Measured
Planetary Boundary Layer from AERI and MPL
Sawyer, Virginia
The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.
A Vertically Resolved Planetary Boundary Layer
NASA Technical Reports Server (NTRS)
Helfand, H. M.
Increase of the vertical resolution of the GLAS Fourth Order General Circulation Model (GCM) near the Earth's surface and installation of a new package of parameterization schemes for subgrid-scale physical processes were sought so that the GLAS Model GCM will predict the resolved vertical structure of the planetary boundary layer (PBL) for all grid points.
Planetary Boundary Layer from AERI and MPL
Sawyer, Virginia
The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.
Heat Transport in the Atmospheric Boundary Layer
L. Mahrt; J. Paumier
The structure of turbulence and transport of heat is examined from data obtained from 11 aircraft soundings executed in heated boundary layers during the Air Mass Transformation Experiment. Various influences on the turbulent transport are revealed by analyzing properties of the joint frequency distribution in polar coordinate. Such an analysis allows determination of a correlation coefficient and fluctuation amplitude as
Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Intermittency Behavior Along the Suction Surface of a Low Pressure Turbine Blade
NASA Technical Reports Server (NTRS)
Schobeiri, M. T.; Ozturk, B.; Ashpis, David E.
The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.
Particle motion in atmospheric boundary layers of Mars and Earth
NASA Technical Reports Server (NTRS)
White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.
To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.
3-D Flow Visualization of a Turbulent Boundary Layer
NASA Astrophysics Data System (ADS)
Thurow, Brian; Williams, Steven; Lynch, Kyle
A recently developed 3-D flow visualization technique is used to visualize large-scale structures in a turbulent boundary layer. The technique is based on the scanning of a laser light sheet through the flow field similar to that of Delo and Smits (1997). High-speeds are possible using a recently developed MHz rate pulse burst laser system, an ultra-high-speed camera capable of 500,000 fps and a galvanometric scanning mirror yielding a total acquisition time of 136 microseconds for a 220 x 220 x 68 voxel image. In these experiments, smoke is seeded into the boundary layer formed on the wall of a low-speed wind tunnel. The boundary layer is approximately 1.5'' thick at the imaging location with a free stream velocity of 24 ft/s yielding a Reynolds number of 18,000 based on boundary layer thickness. The 3-D image volume is approximately 4'' x 4'' x 4''. Preliminary results using 3-D iso-surface visualizations show a collection of elongated large-scale structures inclined in the streamwise direction. The spanwise width of the structures, which are located in the outer region, is on the order of 25 -- 50% of the boundary layer thickness.
Two-fluid boundary layer stability
NASA Astrophysics Data System (ADS)
�zgen, S.; Degrez, G.; Sarma, G. S. R.
The stability of a two-fluid boundary layer is investigated. A boundary layer shears a second fluid that is bounded by the wall and the shearing fluid. The eigenvalue problem governing the linear stability of the configuration is solved using an efficient shooting-search method. Besides the Tollmien-Schlichting mode (hard mode) found in the classical hydrodynamical stability theory an additional Yih-mode (interfacial mode) exists due to the two-fluid interface. Effects of viscosity and density stratifications, thickness of the bounded fluid, gravity, surface tension as well as the non-Newtonian character of the lower fluid on the stability characteristics are determined. The interfacial mode is found to be very sensitive against viscosity stratification. However, with a highly viscous liquid layer, the system approaches a single-layer behavior. The shear-thinning non-Newtonian liquid layer is observed to have a stabilizing effect for both of the modes. Surface tension is stabilizing for short waves for the interfacial mode but a more complex effect was observed for the hard mode. Gravity is stabilizing with a favorable density stratification. Density stratification alone is destabilizing for low and moderate values of this parameter but becomes stabilizing for higher values. When the external boundary layer profile is turbulent, the interfacial mode is more likely to be observed in an experiment. Agreement of the obtained results with experimental, theoretical and numerical results reported in the literature is good. This is encouraging as the study is intended for solving the stability characteristics of de/anti-icing fluid-air systems and comparing the results with the experimental data when they become available.
Control of the Transitional Boundary Layer
NASA Astrophysics Data System (ADS)
Belson, Brandt A.
This work makes advances in the delay of boundary layer transition from laminar to turbulent flow via feedback control. The applications include the reduction of drag over streamline bodies (e.g., airplane wings) and the decrease of mixing and heat transfer (e.g., over turbine blades in jet engines). A difficulty in many fields is designing feedback controllers for high-dimensional systems, be they experiments or high-fidelity simulations, because the required time and resources are too large. A cheaper alternative is to approximate the high-dimensional system with a reduced-order model and design a controller for the model. We implement several model reduction algorithms in "modred", an open source and publicly available library that is applicable to a wide range of problems. We use this library to study the role of sensors and actuators in feedback control of transition in the 2D boundary layer. Previous work uses a feedforward configuration in which the sensor is upstream of the actuator, but we show that the actuator-sensor pair is unsuitable for feedback control due to an inability to sense the exponentially-growing Tollmien-Schlichting waves. A new actuator-sensor pair is chosen that more directly affects and measures the TS waves, and as a result it is effective in a feedback configuration. Lastly, the feedback controller is shown to outperform feedforward controllers in the presence of unmodeled disturbances. Next, we focus on a specific type of actuator, the single dielectric barrier discharge (SDBD) plasma actuator. An array of these plasma actuators is oriented to produce stream-wise vorticity and thus directly cancel the structures with the largest transient growth (so-called stream-wise streaks). We design a feedback controller using only experimental data by first developing an empirical input-output quasi-steady model. Then, we design feedback controllers for the model such that the controllers perform well when applied to the experiment. Lastly, we also simulate the plasma actuators and determine a suitable numerical model for the forces they create by comparing with experimental results. This physical force model is essential to future numerical studies on delaying bypass transition via feedback control and plasma actuation.
Characterizing Boundary Layer Properties for Estimating Urban Greenhouse Gas Emissions
NASA Astrophysics Data System (ADS)
Hardesty, R. M.; Brewer, A.; Sandberg, S.; Weickmann, A.; Sweeney, C.; Karion, A.; Davis, K. J.; Shepson, P. B.; Lauvaux, T.; Cambaliza, M. L.; Miles, N. L.; Whetstone, J. R.
The Indianapolis Flux Experiment (INFLUX) aims to develop, evaluate and improve methodologies for quantification of greenhouse gas fluxes from urban areas through a multi-year modeling and observational study. The study incorporates measurements of greenhouse gases from periodic aircraft observations as well as from a surface-based network of towers in the area. Recently, we installed a scanning Doppler lidar east of downtown Indianapolis to characterize boundary layer properties important for the aircraft and modeling studies. A scan sequence, including conical scans, vertical scans along two orthogonal directions, and zenith staring is repeated every 20 minutes. The lidar measurements of the radial velocity and backscatter intensity are processed to estimate boundary layer depth, turbulent mixing, aerosol distribution, and wind speed and direction. These lidar-derived boundary layer parameters are used in conjunction with the aircraft greenhouse gas concentration measurements in mass-balance studies and for investigating model performance. The lidar wind profile measurements can also be ingested into models to improve inverse flux estimates. We present here an overview of the first several months of lidar observations from Indianapolis, including performance evaluation, comparison with model estimates, diurnal and seasonal variability of the measurements, and use of the data for model ingest. We also discuss different techniques for estimating boundary layer depth from the observations and the application for mass-balance studies, and introduce plans for deploying a second instrument to study horizontal variability of the measured boundary layer properties.
Burst vortex/boundary layer interaction
NASA Technical Reports Server (NTRS)
Bradshaw, P.; Naaseri, M.
Several configurations of delta wing vortex generator and boundary layer test plate were tested, and two final ones selected. Sample measurements and flow visualizations in the candidate configurations, together with more detailed measurements in one of the two final arrangements, which were selected so that a pure vortex bursts repeatably and then interacts, in as simple fashion as possible, with a simple turbulent boundary layer, are included. It is concluded that different intensities of bursting or breakdown, like different strengths of shock wave or hydraulic jump, can be produced by minor changes of configuration. The weaker breakdowns do not produce flow reversal. The initial measurements were done with a fairly weak, but repeatable, breakdown. Basic measurements on the second final arrangement, with a stronger breakdown, are in progress.
Boundary layer transition detection by luminescence imaging
NASA Technical Reports Server (NTRS)
Mclachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.
In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.
Boundary Layer Control for Hypersonic Airbreathing Vehicles
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.
Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.
Linear Controllers for Turbulent Boundary Layers
Junwoo Lim; John Kim; Sung-Moon Kang; Jason Speyer
Several recent studies have shown that controllers based on a linear system theory work surprisingly well in turbulent flows, suggesting that a linear mechanism may play an important role even in turbulent flows. It has been also shown that non-normality of the linearized Navier-Stokes equations is an essential characteristic in the regeneration of near-wall turbulence structures in turbulent boundary layers.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.
Some redesign of the cascade facility was necessary in order to incoporate the requirements of the LDA system into the design. Of particular importance was the intended use of a combination of suction upstream of the blade pack with diverging pack walls, as opposed to blade pack suction alone, for spanwise dimensionality control. An ARL blade was used to redo some tests using this arrangement. Preliminary testing and boundary layer measurements began on the double circular arc blades.
The capillary boundary layer for standing waves
John Miles
The linear, free-surface oscillations of an inviscid fluid in a cylindrical basin subject to the contact-line condition are determined through a boundary-layer approximation. The primary result is a corresponding form factor. Explicit results are derived for circular and rectangular cylinders and compared with Grahem-Eagle's (1983) results for the circular cylinder and Hocking's (1987) results for the two-dimensional problem. The exact
Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions
NASA Technical Reports Server (NTRS)
Wood, William A.; Erickson, David W.; Greene, Francis A.
Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.
Boundary layer cutting in turbulent liquid sheets
NASA Astrophysics Data System (ADS)
Durbin, S. G.; Yoda, M.; Abdel-Khalik, S. I.; Sadowski, D. L.
Turbulent liquid sheets have been proposed to protect solid structures in inertial fusion energy power plants by absorbing damaging radiation and debris. Minimizing surface ripple in these flows will reduce interference with the beams that ignite the fuel and initiate fusion. Wu et al. [Atom. Sprays 5:175 (1995)] showed that ``boundary layer removal'' suppressed primary breakup in turbulent round jets. The effect of boundary layer cutting on the free-surface smoothness of turbulent liquid sheets was therefore studied experimentally for vertical turbulent sheets of water issuing downwards into ambient air. Sheets issuing from a two-dimensional fifth-order polynomial contraction nozzle with an exit aspect ratio of 10 and thickness (small dimension) ? = 1 cm were investigated at Reynolds numbers based on ? up to 1.3 � 10^5. A knife edge is used to ``cut'' away O(0.1 mm) of the flow on one side of the sheet near the nozzle exit. Initial conditions just upstream of the nozzle exit are quantified by laser-Doppler velocimetry. Planar laser-induced fluorescence was used to visualize and measure the free surface geometry of the liquid sheet in the near-field region of this flow up to 25? downstream of the nozzle exit. Boundary layer cutting was shown to significantly reduce surface ripple of the jet as characterized by the standard deviation of the free-surface position.
Momentum Transport in the Convective Boundary Layer
NASA Astrophysics Data System (ADS)
Soares, P. M. M.; Miranda, P. M. A.; Martins, J.; Teixeira, J.
The sub-grid scale transport of momentum in the boundary layer is generally treated as a diffusive process in atmospheric models. However, results for the mean wind are frequently poor in test cases, and it is not clear how important are those fluxes in the performance of the models. Nevertheless, it is clear that convective momentum transport in a key issue in the atmospheric circulation, and in the interactions across multiple space and time scales. In the case of scalar fluxes, such as potential temperature and water vapour, it has been shown that "non-local" transport plays an important role in the turbulent transport, implying that a purely diffusive representation is insufficient. Counter-gradient, mass-flux theories and the combined eddy-diffusivity/mass-flux (EDMF) scheme were built to overcome that problem. The role of non-local effects in momentum is still largely an opened question. In the present study we use a extensive set of results from LES simulations to diagnose vertical profiles of momentum related quantities in different convective boundary layers: the nieuwstadt clear boundary layer, the trade wind cumulus BOMEX case, the shallow cumulus diurnal cycle from the ARM experiment and a LBA deep convection case. In many situations these results show that the momentum transport made by organized structures, as clouds, updraughts and downdraughts contribute significantly to the total turbulent flux, suggesting that they should be included in convective parameterizations.
An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake
NASA Technical Reports Server (NTRS)
Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.
An innovative flow-measuring device, a thermocouple boundary layer rake, was developed. The sensor detects the flow by using a thin-film thermocouple (TC) array to measure the temperature difference across a heater strip. The heater and TC arrays are microfabricated on a constant-thickness quartz strut with low heat conductivity. The device can measure the velocity profile well into the boundary layer, about 65 gm from the surface, which is almost four times closer to the surface than has been possible with the previously used total pressure tube.
Numerical Study of Boundary-Layer in Aerodynamics
NASA Technical Reports Server (NTRS)
Shih, Tom I-P.
The accomplishments made in the following three tasks are described: (1) The first task was to study shock-wave boundary-layer interactions with bleed - this study is relevant to boundary-layer control in external and mixed-compression inlets of supersonic aircraft; (2) The second task was to test RAAKE, a code developed for computing turbulence quantities; and (3) The third task was to compute flow around the Ames ER-2 aircraft that has been retrofitted with containers over its wings and fuselage. The appendices include two reports submitted to AIAA for publication.
Effects of forebody geometry on subsonic boundary-layer stability
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
As part of an effort to develop computational techniques for design of natural laminar flow fuselages, a computational study was made of the effect of forebody geometry on laminar boundary layer stability on axisymmetric body shapes. The effects of nose radius on the stability of the incompressible laminar boundary layer was computationally investigated using linear stability theory for body length Reynolds numbers representative of small and medium-sized airplanes. The steepness of the pressure gradient and the value of the minimum pressure (both functions of fineness ratio) govern the stability of laminar flow possible on an axisymmetric body at a given Reynolds number. It was found that to keep the laminar boundary layer stable for extended lengths, it is important to have a small nose radius. However, nose shapes with extremely small nose radii produce large pressure peaks at off-design angles of attack and can produce vortices which would adversely affect transition.
The Role of Boundary Layer Processes in Limiting PV Homogenization
Zhang, Yang
A ?-plane multilevel quasigeostrophic channel model with interactive static stability and a simplified parameterization of atmospheric boundary layer physics is used to study the role of different boundary layer processes ...
Accommodation between transpiring vegetation and the convective boundary layer
J. L. Monteith
A simple scheme is developed to describe how vegetation and the convective boundary layer (CBL) interact during daylight in terms of water and sensible heat exchange. The response of vegetation to a prescribed atmospheric state is defined by a quadratic equation obtained by combining the Penman-Monteith equation with a new relation between surface conductance and transpiration rate based on laboratory
A brief review is made of data bases which have been used for developing diffusion parameterizations for the convective boundary layer (CBL). A variety of parameterizations for lateral and vertical dispersion, (sigma sub) and (sigma sub z), are surveyed; some of these include mec...
Entrainment effects in the well-mixed atmospheric boundary layer
A. G. M. Driedonks; H. Tennekes
We discuss the structure and evolution of a cloud-free atmospheric boundary layer (ABL) during daytime over land, starting from a shallow ABL at sunrise and developing into a deep ABL with strong convection in the afternoon. The structure of the turbulence in the lower half of a convective ABL capped by an inversion is reasonably well understood. Less is known
On Tollmien�Schlichting-like waves in streaky boundary layers
Carlo Cossu; Luca Brandt
The linear stability of the boundary layer developing on a flat plate in the presence of finite-amplitude, steady and spanwise periodic streamwise streaks is investigated. The streak amplitudes considered here are below the threshold for onset of the inviscid inflectional instability of sinuous perturbations. It is found that, as the amplitude of the streaks is increased, the most unstable viscous
Quasi-Coherent Structures In Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Robinson, S. K.; Kline, S. J.; Spalart, P. R.
Two-part report reviews knowledge of coherent structures in turbulent boundary layers. Part I describes processes and status of cooperative project to summarize data from research on boundary-layer turbulence. Part II presents results of study of numerically simulated flat-plate canonical turbulent boundary layer.
Ivar G. Jonsson; Niels A. Carlsen
The oscillatory flow near the sea bed under a wave motion is always rough turbulent in a coastal zone. This type of an oscillatory boundary layer (or �wave boundary layer�) was therefore chosen as a subject for detailed velocity measurements, from which characteristics such as shear stresses, eddy viscosities, energy loss, and boundary layer thickness were determined.
Thermal Effects in the Atmospheric Boundary Layer above the North
Heinemann, Detlev
Thermal Effects in the Atmospheric Boundary Layer above the North Sea by Saskia Tautz A thesis Background 6 2.1 Atmospheric Boundary Layer . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Basics.1.5 Fluxes in the Boundary layer . . . . . . . . . . . . . . . . 8 2.2 Measurement of Fluxes
Near surface turbulence in a smooth wall atmospheric boundary layer
Morris, Scott C.
1 Near surface turbulence in a smooth wall atmospheric boundary layer Scott C. Morris (s is to acquire measurements in the atmospheric boundary layer. For example, Van Atta and Chen (1970) used hot-wires in the atmospheric boundary layer over an ocean sur- face to learn more about structure functions in wall bounded
CIRES Research Associate Arctic Cloud and Boundary Layer Processes
Colorado at Boulder, University of
for a research associate, postdoctoral scientist to study Arctic atmospheric boundary- layer processes, the atmospheric boundary layer and the surface in the Arctic environment using existing observational data setsCIRES Research Associate Arctic Cloud and Boundary Layer Processes The Cooperative Institute
OFFSHORE BOUNDARY-LAYER MODELLING H. Bergstrm1
for this are excluded. Field experiments in the Baltic Sea area, [1], have shown that the atmospheric boundary layer farOFFSHORE BOUNDARY-LAYER MODELLING H. Bergstr�m1 and R. Barthelmie2 1) Uppsala Univ., Dept. of Earth and low-level jets. The paper describes results from the boundary-layer modelling work package (WP4
Passive and active control of boundary layer transition
NASA Astrophysics Data System (ADS)
Nosenchuck, Daniel Mark
It is well known that laminar-turbulent boundary layer transition is initiated by the formation of Tollmien-Schlichting laminar instability waves. The amplification rates of these waves are strongly dependent on the shape of the boundary layer velocity profile. Consequently, the transition process can be controlled by modifying the velocity profile. This can be accomplished by controlling the pressure gradient (dp/dx), using boundary layer suction, installing surface roughness elements, or by surface heating or cooling. Methods used to modify the transition process through changes in the mean velocity profile are called "passive" in this paper. There exists a large set of experiments and theory on the application of passive methods for boundary layer control. In the present work only surface heating will be addressed.Transition measurements were made on a heated flat plate in water. Results are presented for several plate wall temperature distributions. An increase by a factor of 2.5 in transition Reynolds number was observed for a 5�C isothermal wall overheat. Buoyancy effects on transition were minimal due to the small Richardson and Grashof numbers encountered in the experiments.The amplification of laminar instability waves is comparatively to process, taking place over many boundary layer thicknesses. After the slow amplification of the laminar instability waves, transition occurs by a strong three dimensional dynamic instability. It appears possible to attenuate (or reinforce) the instability waves by introducing amplitude-and phase-controlled perturbations into the laminar boundary layer using feedback control system. This method is called "active" control and forms the larger part of the research reported in this thesis.A combination of sensors, activators and feedback control electronics is required for active control. The sensors used in the experiments are flush-mounted hot film wall shear robes. A new type of activator was developed using thin, flush-mounted surface heating elements to excite instability waves in the laminar boundary layer by periodic (active) heating.Experimental evidence is presented illustrating the effects of periodically heated flush mounted strips in perturbing a flat plate boundary layer in water. The results of superposition of forced laminar instability waves are also given. Finally, an active feedback-control system using a single hot film probe and strip heater was developed to control natural laminar instability waves in real time. It is shown that when the natural waves were attenuated, the transition length was increased by 25%, requiring only 10 watts of strip heater power. To accomplish the same transition delay using passive heating, the internal heating pads had to supply 1900 watts of power.
Application of a general boundary layer analysis to turbulent boundary layers subjected to strong favorable pressure gradients
J. P. Kreskovsky; S. J. Shamroth; H. McDonald
Theoretical predictions of turbulent boundary layer development under the influence of strong favorable pressure gradients made using a finite-difference calculation procedure are compared to experimental data. Comparisons are presented for low speed flows with and without wall heat transfer as well as for supersonic flows with adiabatic walls. The turbulence model used is governed by an integral form of the
A study of unsteady turbulent boundary layer separation under conditions relevant to helicopter rotor dynamics
NASA Astrophysics Data System (ADS)
Schatzman, David M.
An experimental investigation focused on the study of the physics of unsteady turbulent boundary layer separation under conditions relevant to the dynamic stall process that occurs in helicopter rotors is presented. A flat boundary layer development plate allows for the growth of a turbulent boundary layer of thickness sufficient for high spatial resolution measurements. Downstream of the flat plate, a convex ramp section imposes a streamwise adverse pressure gradient that gives rise to boundary layer separation. In order to impose an unsteady pressure gradient, an airfoil equipped with leading edge plasma flow control is located above the ramp section. Plasma flow control is used to alternately attach and separate the airfoil flow which gives rise to unsteady turbulent boundary layer separation on the convex ramp. Measurements of the resulting unsteady turbulent boundary layer separation via phase-locked two-component PIV, unsteady surface pressure measurements, and high speed digital imaging capture and quantify the dynamics the separation process at the wall and throughout the unsteady boundary layer. Two-component LDA measurements are used to characterize the motions of ejection and sweep events within the unsteady boundary layer using a quadrant splitting technique. Large amplitude quadrant 4 sweep events are the most dynamically significant in the near wall region during the unsteady separation process. The adverse pressure gradient boundary layer profiles throughout the unsteady cycle collapse remarkably well when scaled with embedded shear layer parameters. The implications of the experimental results for the development of flow control strategies for unsteady boundary layer separation are discussed.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.
Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Berry, Scott A.; Hollis, Brian R.; Horvath, Thomas J.
Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.
The minisodar and planetary boundary layer studies
Coulter, R.L.
The minisodar, in addition to being smaller than conventional sodar, operates at higher frequencies, obtains usable signal returns closer to the surface, and can use smaller range gates. Because the max range is generally limited to the lower 200 m above the surface, the minisodar is not able to interrogate the entire daytime atmospheric Planetary Boundary Layer (PBL); however it can be a very useful tool for understanding the PBL. In concert with other instruments, the minisodar can add significant new insights to our understanding of the PBL. This paper gives examples of past and potential uses of minisodars in such situations.
Coherent motions in the turbulent boundary layer
NASA Technical Reports Server (NTRS)
Robinson, Stephen K.
The role of coherent structures in the production and dissipation of turbulence in a boundary layer is characterized, summarizing the results of recent investigations. Coherent motion is defined as a three-dimensional region of flow where at least one fundamental variable exhibits significant correlation with itself or with another variable over a space or time range significantly larger than the smallest local scales of the flow. Sections are then devoted to flow-visualization experiments, statistical analyses, numerical simulation techniques, the history of coherent-structure studies, vortices and vortical structures, conceptual models, and predictive models. Diagrams and graphs are provided.
Boundary-layer Transition at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Low, George M
Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.
The flow field about an airfoil in cascade at a Reynolds number of 5 x 10 to the 5th power is described. Hot wire and laser anemometry are combined with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation, and the transition zone) on a cascade of relatively highly loaded blades. Benchmark data is provided for the evaluation of current and future predictive models, in this way aiding in the compressor design process.
The influence of bulges on boundary-layer instability
NASA Technical Reports Server (NTRS)
Elli, S.; Vandam, C. P.
Local disturbances caused by a spanwise surface corrugation affect the position of the boundary-layer transition, and so the drag, of an object. This premature transition from laminar to turbulent flow is often associated with a separation of the laminar boundary-layer from its surface. Also the roughness-induced separation bubble provides an important link between the pressure and velocity fluctuations in the environment and the development of the disturbance in the laminar boundary-layer, i.e., the receptivity problem. To investigate the influence of a laminar separation bubble on boundary-layer instability, a separated flow generated by a velocity gradient over a flat plate was analyzed by direct numerical simulation using finite-difference solutions of the Navier-Stokes equations. The bubble acts as a strong amplifier of the instability waves and a highly nonlinear flow field is shown to develop downstream of the bubble. Consequently, the results of the direct numerical simulation differ noticeably from those of the classical linear stability theory proving the fact that the nonparallel effects together with the nonlinear interactions are crucial to this flow development. In the present paper, the effect of physical perturbations such as humps and hollows on boundary-layer instability is analyzed. This problem has been considered theoretically by several researchers (e.g., Nayfeh et al., 1987 and 1990; Cebeci et al., 1988). They used linear stability theory in their approach which does not include the nonparallel nor the nonlinear effects. Therefore, to account for these important effects in studying flow over humps and hollows the direct simulation technique is being implemented in generalized coordinates.
The influence of bulges on boundary-layer instability
NASA Astrophysics Data System (ADS)
Elli, S.; Vandam, C. P.
Local disturbances caused by a spanwise surface corrugation affect the position of the boundary-layer transition, and so the drag, of an object. This premature transition from laminar to turbulent flow is often associated with a separation of the laminar boundary-layer from its surface. Also the roughness-induced separation bubble provides an important link between the pressure and velocity fluctuations in the environment and the development of the disturbance in the laminar boundary-layer, i.e., the receptivity problem. To investigate the influence of a laminar separation bubble on boundary-layer instability, a separated flow generated by a velocity gradient over a flat plate was analyzed by direct numerical simulation using finite-difference solutions of the Navier-Stokes equations. The bubble acts as a strong amplifier of the instability waves and a highly nonlinear flow field is shown to develop downstream of the bubble. Consequently, the results of the direct numerical simulation differ noticeably from those of the classical linear stability theory proving the fact that the nonparallel effects together with the nonlinear interactions are crucial to this flow development. In the present paper, the effect of physical perturbations such as humps and hollows on boundary-layer instability is analyzed. This problem has been considered theoretically by several researchers (e.g., Nayfeh et al., 1987 and 1990; Cebeci et al., 1988). They used linear stability theory in their approach which does not include the nonparallel nor the nonlinear effects. Therefore, to account for these important effects in studying flow over humps and hollows the direct simulation technique is being implemented in generalized coordinates.
Sound radiation due to boundary layer transition
NASA Technical Reports Server (NTRS)
Wang, Meng
This report describes progress made to date towards calculations of noise produced by the laminar-turbulence transition process in a low Mach number boundary layer formed on a rigid wall. The primary objectives of the study are to elucidate the physical mechanisms by which acoustic waves are generated, to clarify the roles of the fluctuating Reynolds stress and the viscous stress in the presence of a solid surface, and to determine the relative efficiency as a noise source of the various transition stages. In particular, we will examine the acoustic characteristics and directivity associated with three-dimensional instability waves, the detached high-shear layer, and turbulent spots following a laminar breakdown. Additionally, attention will be paid to the unsteady surface pressures during the transition, which provide a source of flow noise as well as a forcing function for wall vibration in both aeronautical and marine applications.
Linear and nonlinear stability of the Blasius boundary layer
NASA Technical Reports Server (NTRS)
Bertolotti, F. P.; Herbert, TH.; Spalart, P. R.
Two new techniques for the study of the linear and nonlinear instability in growing boundary layers are presented. The first technique employs partial differential equations of parabolic type exploiting the slow change of the mean flow, disturbance velocity profiles, wavelengths, and growth rates in the streamwise direction. The second technique solves the Navier-Stokes equation for spatially evolving disturbances using buffer zones adjacent to the inflow and outflow boundaries. Results of both techniques are in excellent agreement. The linear and nonlinear development of Tollmien-Schlichting (TS) waves in the Blasius boundary layer is investigated with both techniques and with a local procedure based on a system of ordinary differential equations. The results are compared with previous work and the effects of non-parallelism and nonlinearity are clarified. The effect of nonparallelism is confirmed to be weak and, consequently, not responsible for the discrepancies between measurements and theoretical results for parallel flow.
The role of acoustic feedback in boundary-layer instability
NASA Astrophysics Data System (ADS)
Wu, Xuesong
In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which acoustic feedback loop plays an essential role. The first concerns a boundary layer over a flat plate, on which two well separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave, which propagates upstream and impinges on the upstream roughness to regenerate the T-S wave thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that at high Reynolds numbers and for moderate roughness heights the long-range acoustic coupling may lead to global instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns supersonic 'twin boundary layers', which develop along the two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the usual unconfined boundary layer.
On the Effects of Surface Roughness on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack
Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.
X-33 Hypersonic Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II
Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.
Boundary Layer Transition Flight Experiment Overview
NASA Technical Reports Server (NTRS)
Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.
In support of the Boundary Layer Transition Flight Experiment (BLT FE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for STS-119, STS-128, STS-131 and STS-133 as well as Space Shuttle Endeavour for STS-134. Additional instrumentation was installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLT FE Project with emphasis on the STS-131 and STS-133 results. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that empirically correlated predictions for boundary layer transition onset time closely match the flight data, while predicted surface temperatures were significantly higher than observed flight temperatures. A thermocouple anomaly observed on a number of the missions is discussed as are a number of the mitigation actions that will be taken on the final flight, STS-134, including potential alterations of the flight trajectory and changes to the flight instrumentation.
Boundary layer flow on a vibrating surface
NASA Astrophysics Data System (ADS)
Carlsson, Fredrik; Bakchinov, Andrey; L�fdahl, Lennart
Boundary layers subjected to vibrating surfaces occur in many engineering applications. The surfaces of vehicles may vibrate, for instance, a ship�s hull vibrates at varying eigenfrequencies and eigenmodes due to the power plant of these vessels. There is little information available on this subject, and it is therefore not generally understood how these vibrations affect the fluid flows on the vibrating surface. To investigate these phenomena in greater detail, a test rig is designed and evaluated. The rig consists of a vibrating surface attached to a larger flat plate mounted in a low-speed wind tunnel. Two-dimensional vibrations of the surface in the fundamental mode are considered, and therefore the vibrating surface is clamped only on two sides to the flat plate. The surface is excited in the centerline using a crankshaft with adjustable amplitude (0-5 mm), designed and manufactured for this purpose. A frequency range of zero up to the first fundamental frequency of the surface can be studied. Detailed information of the rig and its performance characteristics along with preliminary measurements in the boundary layer over the vibrating surface will be presented.
Sound Radiation from a Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Laufer, J.
If the restriction of incompressibility in the turbulence problem is relaxed, the phenomenon of energy radiation in the form of sound from the turbulent zone arises. In order to calculate this radiated energy, it is shown that new statistical quantities, such as time-space correlation tensors, have to be known within the turbulent zone in addition to the conventional quantities. For the particular case of the turbulent boundary layer, indications are that the intensity of radiation becomes significant only in supersonic flows. Under these conditions, the recent work of Phillips is examined together with some experimental findings of the author. It is shown that the qualitative features of the radiation field (intensity, directionality) as predicted by the theory are consistent with the measurements; however, even for the highest Mach number flow, some of the assumptions of the asymptotic theory are not yet satisfied in the experiments. Finally, the question of turbulence damping due to radiation is discussed, with the result that in the Mach number range covered by the experiments, the energy lost from the boundary layer due to radiation is a small percentage of the work done by the wall shearing stresses.
Progress in the development of a two-fluid model of turbulence for near-wall flows. Part 3: Preliminary investigation of a stably-stratified boundary layer
J. O. Ilegbusi
A compressible form of the two-fluid turbulence model is postulated. It includes buoyancy effects in the momentum equation and in the determination of the fragment size. The model is applied to a wall boundary-layer flow at low Mach number, with the difference between the stream and wall temperatures large enough for fluid properties to vary. Results show a substantial reduction
Study of boundary-layer transition using transonic-cone preston tube data
NASA Technical Reports Server (NTRS)
Reed, T. D.; Moretti, P. M.
The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones.
The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer. Ph.D. Thesis - Case Western Reserve Univ.
NASA Technical Reports Server (NTRS)
Wendt, Bruce J.; Greber, Isaac; Hingst, Warren R.
An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization of vortex structure. Vortex structure was characterized by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen Vortex. Vortex trajectories are modelled by including the convective effects of neighbors.
Large eddy simultations of the atmospheric boundary layer east of the Colorado Rockies
Costigan, K.R.; Cotton, W.R.
Large eddy simulation, LES, has often been carried out for the idealized situation of a simple convective boundary layer. Studies of dual Doppler radar and aircraft data from the Phoenix II experiment indicate that the boundary layer of the Colorado High Plains is not a purely convective boundary layer and it is influenced by the mountains to the west. The purpose of this study is to investigate the atmospheric boundary layer on one particular day on the Colorado High Plains. This research applies a LES nested within larger grids, which contain realistic topography and can simulate the larger-scale circulations initiated by the presence of the mountain barrier. How and to what extent the atmospheric boundary layer of the Colorado High Plains is influenced by larger scale circulations and other phenomena associated with the mountain barrier to the west is investigated. The nested grid LES reproduces the characteristics of the atmosphere for the case study day reasonably well. The mountains influence the atmospheric boundary layer over the plains to the east in several ways. The mountains contribute to the vertical shear of the horizontal winds through the thermally-induced mountain-plains circulation. As a consequence of the wind shear, the boundary layer that develops over the mountains is advected eastward over the top of the plains boundary layer, which is developing separately. This layer is marked by a mixture of gravity waves and turbulence and is atypical of a purely convective boundary layer. Just below this layer, the capping inversion of the plains boundary layer is weak and poorly defined compared to the inversions capping purely convective boundary layers. Gravity waves, triggered by the obstacle of the Rocky Mountains and by convection in the mountain boundary layer, also influence the atmosphere above the Colorado High Plains. These influences are found to have significant effects on the turbulence statistics and the energy spectra.
Belyaev, Mikhail A.; Rafikov, Roman R., E-mail: email@example.com [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)
Disk accretion onto weakly magnetized astrophysical objects often proceeds via a boundary layer (BL) that forms near the object's surface, in which the rotation speed of the accreted gas changes rapidly. Here, we study the initial stages of formation for such a BL around a white dwarf or a young star by examining the hydrodynamical shear instabilities that may initiate mixing and momentum transport between the two fluids of different densities moving supersonically with respect to each other. We find that an initially laminar BL is unstable to two different kinds of instabilities. One is an instability of a supersonic vortex sheet (implying a discontinuous initial profile of the angular speed of the gas) in the presence of gravity, which we find to have a growth rate of order (but less than) the orbital frequency. The other is a sonic instability of a finite width, supersonic shear layer, which is similar to the Papaloizou-Pringle instability. It has a growth rate proportional to the shear inside the transition layer, which is of order the orbital frequency times the ratio of stellar radius to the BL thickness. For a BL that is thin compared to the radius of the star, the shear rate is much larger than the orbital frequency. Thus, we conclude that sonic instabilities play a dominant role in the initial stages of nonmagnetic BL formation and give rise to very fast mixing between disk gas and stellar fluid in the supersonic regime.
Transitional and turbulent boundary layer with heat transfer
NASA Astrophysics Data System (ADS)
Wu, Xiaohua; Moin, Parviz
We report on our direct numerical simulation of an incompressible, nominally zero-pressure-gradient flat-plate boundary layer from momentum thickness Reynolds number 80-1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number Pr=1. Skin-friction coefficient and other boundary layer parameters follow the Blasius solutions prior to the onset of turbulent spots. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cf deviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Mean velocity and Reynolds stresses agree with experimental data over an extended turbulent region downstream of transition. Normalized rms wall-pressure fluctuation increases gradually with the streamwise growth of the turbulent boundary layer. Wall shear stress fluctuation, ?w,rms'+, on the other hand, remains constant at approximately 0.44 over the range, 800
Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Hess, Robert V.
An appraisal is made of existing solutions of magnetohydrodynamic boundary-layer equations for stagnation flow and flat-plate flow, and some new solutions are given. Since an exact solution of the equations of magnetohydrodynamics requires complicated simultaneous treatment of the equations of fluid flow and of electromagnetism, certain simplifying assumptions are generally introduced. The full implications of these assumptions have not been brought out properly in several recent papers. It is shown in the present report that for the particular law of deformation which the magnetic lines are assumed to follow in these papers a magnet situated inside the missile nose would not be able to take up any drag forces; to do so it would have to be placed in the flow away from the nose. It is also shown that for the assumption that potential flow is maintained outside the boundary layer, the deformation of the magnetic lines is restricted to small values. The literature contains serious disagreements with regard to reductions in heat-transfer rates due to magnetic action at the nose of a missile, and these disagreements are shown to be mainly due to different interpretations of reentry conditions rather than more complicated effects. In the present paper the magnetohydrodynamic boundary-layer equation is also expressed in a simple form that is especially convenient for physical interpretation. This is done by adapting methods to magnetic forces which in the past have been used for forces due to gravitational or centrifugal action. The simplified approach is used to develop some new solutions of boundary-layer flow and to reinterpret certain solutions existing in the literature. An asymptotic boundary-layer solution representing a fixed velocity profile and shear is found. Special emphasis is put on estimating skin friction and heat-transfer rates.
Nonlocal boundary layer: The pure buoyancy-driven and the buoyancy-shear-driven cases
N. M. Colonna; E. Ferrero; U. Rizza
A Reynolds-averaged Navier-Stokes (RANS) model including nonlocality was developed and tested. The aim of this paper was to investigate different boundary layer conditions with the RANS model. In particular we focused our attention on boundary layers where convection plays a major role: the shear-free buoyancy-driven boundary layer and the buoyancy-shear-driven one. We presented a new model which solves dynamical equations
Simulation of Atmospheric Boundary Layer Processes Using Local and Nonlocal-Closure Schemes
Kiran Alapaty; Jonathan E. Pleim; Sethu Raman; Devdutta S. Niyogi; Daewon W. Byun
A soil-vegetation-atmospheric boundary layer model was developed to study the performance of two local- closure and two nonlocal-closure boundary layer mixing schemes for use in meteorological and air quality simulation models. Full interaction between the surface and atmosphere is achieved by representing surface characteristics and associated processes using a prognostic soil-vegetation scheme and atmospheric boundary layer schemes. There are 30
Works on theory of flapping wing. [considering boundary layer
NASA Technical Reports Server (NTRS)
Golubev, V. V.
It is shown mathematically that taking account of the boundary layer is the only way to develop a theory of flapping wings without violating the basic observations and mathematics of hydromechanics. A theory of thrust generation by flapping wings can be developed if the conventional downstream velocity discontinuity surface is replaced with the observed Karman type vortex streets behind a flapping wing. Experiments show that the direction of such vortices is the reverse of that of conventional Karman streets. The streets form by breakdown of the boundary layer. Detailed analysis of the movements of certain birds and insects during flight 'in place' is fully consistent with this theory of the lift, thrust and drag of flapping wings. Further directions for research into flight with flapping wings are indicated.
J. Zueco; O. Anwar B�g
The study of a steady coupled dissipative layer, known as the Mangaroni mixed convection boundary layer, in the presence of a magnetic field is presented. The mixed convection boundary layer is generated when in addition to Marangoni (thermocapillary) effects there are also buoyancy effects due to gravity and external pressure gradient effects. In the model considered the Marangoni coupling condition
Formal Derivation of Boundary Layers in Fluid Mechanics
David Gerard-Varet; G. Iooss
Boundary layers appear in various areas of fluid dynamics, as oceanology, meteorology, or magnetohydrodynamics (MHD). Some of them are already mathematically well known, like the Ekman layers. Many others remain unstudied, and can be much more complex. The aim of this paper is to give both a unified presentation of the main boundary layers, and a simple method to derive
Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the atmospheric boundary layer
Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.
A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform's operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.
Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the atmospheric boundary layer
Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.
A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform`s operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.
Vortex/boundary-layer interactions: Data report, volume 1
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Bradshaw, P.
This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in course of preparation.
Vortex/boundary-layer interactions: Data report, volume 2
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Bradshaw, P.
This report summarizes the work done under NASA grant NAGw-581, Vortex/Boundary-Layer Interactions, to date. The experimental methods are discussed in detail and the results presented as a large number of figures, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in preparation.
Boundary Layer Transition Experiments in Support of the Hypersonics Program
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Chen, Fang-Jenq; Wilder, Michael C.; Reda, Daniel C.
Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.
BLSTA: A boundary layer code for stability analysis
NASA Technical Reports Server (NTRS)
Wie, Yong-Sun
A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.
Acoustics of laminar boundary layers breakdown
NASA Technical Reports Server (NTRS)
Wang, Meng
Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.
Halogen chemistry in the marine boundary layer
NASA Astrophysics Data System (ADS)
Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.
Important atmospheric sources of iodine include the air-sea exchange of biogenic iodocarbons, and the emission of I2 from macro-algae. The major source of bromine is the release of bromide ions from sea-salt aerosol. The subsequent atmospheric chemistry of these halogens (1), changes the oxidizing capacity of the marine boundary layer by destroying ozone and changing the hydroxyl radical concentration; (2), reacts efficiently with dimethyl sulphide and mercury (in the polar regions); and (3), leads to the formation of ultra-fine particles which may contribute to cloud condensation nuclei (CCN) and hence affect climate. This paper will report observations of IO, BrO, OIO and I2 made by the technique of differential optical absorption spectroscopy, in several contrasting marine environments: the equatorial mid-Atlantic (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar marine boundary layer (Hudson Bay, Canada). Both IO and BrO are observed in all these locations at significant concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. To complement the field campaigns we have also carried out wide-ranging laboratory investigation. A new study of OIO photochemistry shows that absorption in the visible bands between 490 and 630 nm leads to I atom production with a quantum yield of unity, which now means that iodine is a particularly powerful ozone-depleting agent. We have also studied the formation and growth kinetics of iodine oxide nano-particles, and their uptake of water, sulphuric acid and di-carboxylic organic acids, in order to model their growth to a size where they can act as CCN. Their ice-nucleating properties will also be reported.
Active Boundary Layer Trip for Supersonic Flows
NASA Astrophysics Data System (ADS)
Schloegel, F.; Panigua, G.; Tirtey, S.
The last decade has been full of excitement and success for the hypersonic community thanks to various Scramjet ground tests and launches. These studies have shown promising potentials but the viability to perform commercial flights at Mach 8 is still to be demonstrated. An ideal Scramjet is one which is capable of self- starting over a wide range of angles of attack and Mach number. The Scramjet designer has to ensure that the boundary layer over the inlet ramp is fully turbulent where shocks impact, hence reducing the risks of chocked flow conditions. Most studies have issued the efficiency of roughness trip to trigger the boundary layer transition. At hypersonic speed, heat transfer and drag dramatically increase resulting in skin friction averaging at 40% of the overall drag. This study investigates the possibility of triggering transition using perpendicular air jets on a flat plate place in a hypersonic cross-flow. Experiments were conducted in the von Karman Institute hypersonic blow down wind tunnel H3. This facility is mounted with a Mach 6 contoured nozzles and provides flows with Reynolds number in the range of 10x106/m to 30x106/m. The model consist of a flat plate manufactured with a built -in settling chamber, equipped with a pressure tap and a thermocouple to monitor the jet conditions. A first flat plate was manufactured with a black-coated Plexiglas top, for surface heat transfer measurement using an infrared camera. On the second model, a Upilex sheet equipped with 32 thin film gages was glued, time dependent heat transfer measurements up to 60kHz. The jet injection conditions have been varied and a Mach number of 5.5 kept constant. The flow topology was investigated using fast schlieren techniques and oil flow, in order to gain a better understanding.
Winds in the Marine Boundary Layer: A Forecaster's Guide
NSDL National Science Digital Library
This module is intended for experienced forecasters moving from a land-based area to a coastal or Great Lakes region where both over-land and over-water forecast areas exist. This module highlights the differences between marine boundary layer and terrestrial boundary layer winds. The experienced forecaster is relatively familiar with the boundary layer over land and the associated implications for the wind field. Using this as a base, the module compares this known quantity with the lesser-known processes that occur in the marine boundary layer. Three major topics that influence marine boundary layer winds are discussed: stability within the boundary layer, isallobaric influence, and the effects of convection and tropical cyclones.
A modeling study of marine boundary layer clouds
NASA Technical Reports Server (NTRS)
Wang, Shouping; Fitzjarrald, Daniel E.
Marine boundary layer (MBL) clouds are important components of the earth's climate system. These clouds drastically reduce the amount of solar radiation absorbed by the earth, but have little effect on the emitted infrared radiation on top of the atmosphere. In addition, these clouds are intimately involved in regulating boundary layer turbulent fluxes. For these reasons, it is important that general circulation models used for climate studies must realistically simulate the global distribution of the MBL. While the importance of these cloud systems is well recognized, many physical processes involved in these clouds are poorly understood and their representation in large-scale models remains an unresolved problem. The present research aims at the development and improvement of the parameterization of these cloud systems and an understanding of physical processes involved. This goal is addressed in two ways. One is to use regional modeling approach to validate and evaluate two-layer marine boundary layer models using satellite and ground-truth observations; the other is to combine this simple model with a high-order turbulence closure model to study the transition processes from stratocumulus to shallow cumulus clouds. Progress made in this effort is presented.
Experiment on convex curvature effects in turbulent boundary layers.
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
Turbulent boundary layers along a convex surface of varying curvature were investigated in a specially designed boundary-layer tunnel. A fairly complete set of turbulence measurements was obtained. The effect of curvature is striking. For example, along a convex wall the Reynolds stress is decreased near the wall and vanishes about midway between the wall and the edge of a boundary layer where there exists a velocity profile gradient created upstream of the curved wall.
Boundary Layer Transition Flight Experiment Implementation on OV-103
NASA Technical Reports Server (NTRS)
Spanos, Theodoros A.
This slide presentation reviews the boundary layer transition experiment flown on Discovery. The purpose of the boundary layer transition flight experiment was to obtain hypersonic aero-thermodynamic data for the purpose of better understanding the flow transition from a laminar to turbulent boundary layer using a known height protuberance. The preparation of the shuttle is described, with the various groups responsibilities outlined. Views of the shuttle in flight with the experimental results are shown.
Wind flow over ridges in simulated atmospheric boundary layers
J. R. Pearse; D. Lindley; D. C. Stevenson
The flows over four two-dimensional triangular hills and three two-dimensional bell-shaped hills have been investigated in a simulated rural atmospheric boundary layer modelled to a scale of 1:300: Further measurements were made over two of the triangular hills in a simulated rural boundary layer of 1: 3000 scale and in a simulated urban boundary layer modelled to a scale of
Stratified Atmospheric Boundary Layers and Breakdown of Models
L. Mahrt
:�� The goal of this study is to assess complications in atmospheric stable boundary layers which are not included in numerical\\u000a models of the stably stratified boundary layer and to provide a formulation of surface fluxes for use in numerical models.\\u000a Based on an extensive interpretive literature survey and new eddy correlation data for the stable boundary layer, this study
Electromagnetic precipitation and ducting of particles in turbulent boundary layers
NASA Technical Reports Server (NTRS)
Davey, K. R.; Melcher, J. R.
A method for analyzing magnetic migration of particles in turbulent flows is applied to the prediction of particle trajectories and densities in turbulent aerodynamic boundary layers. Results for conditions typical of aircraft with 30-40 micron particles indicate a large upstream collection and a 5% loss of particles during one pass through the boundary layer. The capacity of the magnetic field to achieve a balance with turbulent diffusion in confining the particles to the boundary layer is discussed.
Seasonal Simulations of the Planetary Boundary Layer and Boundary-Layer Stratocumulus Clouds with a General Circulation Model
David A. Randall; James A. Abeles; Thomas G. Corsetti
The UCLA general circulation model (GCM) has been used to simulate the seasonally varying planetary boundary layer (PBL), as well as boundary-layer stratus and stratocumulus clouds. The PBL depth is a prognostic variable of the GCM, incorporated through the use of a vertical coordinate system in which the PBL is identified with the lowest model layer.Stratocumulus clouds are assumed to
Airship Observations of Formaldehyde in the Po Valley as a Probe of Boundary Layer Development and Non-Classical Radical Chemistry
NASA Astrophysics Data System (ADS)
Kaiser, J.; Wolfe, G. M.; Keutsch, F. N.
Stagnant meteorological conditions and high anthropogenic emissions make the Po Valley in Northern Italy one of Europe's most polluted regions. Understanding the processes controlling ozone production in this environment is essential for developing effective mitigation strategies. As both a source of HO2 radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. During the Pan-European Gas-AeroSOls Climate Interaction Study (PEGASOS), HCHO measurements were acquired via a Fiber Laser-Induced Fluorescence (FiLIF) instrument onboard a Zeppelin airship. This mission represents the first successful airborne deployment of the FiLIF instrument. With low flight speeds and vertical profiling capabilities, these Zeppelin-based observations in conjunction with other measurements may offer new insights into the spatial and temporal variability of atmospheric composition within the Po Valley region. Preliminary comparisons of modeled and measured HCHO concentrations at various altitudes and VOC/NOx regimes will be presented. Analysis will focus on 1) the transition from nocturnal to daytime boundary layers, and 2) the potential role of "non-classical" radical chemistry in ozone production.
Observations of the magnetospheric boundary layers. [International Magnetospheric Study
NASA Technical Reports Server (NTRS)
Eastman, T. E.
Results on magnetospheric boundary layers are reviewed, emphasizing their dynamical importance based on hot plasma observations, energetic particle signatures, heavy ion contributions and the effects of wave-particle interactions. Satellite plasma observations show that 1% to 2% of the oncoming solar wind plasma enters the magnetosphere and is initially transported within the magnetospheric boundary layer. Some of this boundary layer plasma is entrained within the Earth's magnetotail where it can be accelerated. Tests are needed to determine the relative contributions of the primary acceleration processes whose effects are especially evident in the plasma sheet boundary layer.
The effect of an aircraft's boundary layer on propeller noise
NASA Astrophysics Data System (ADS)
Belyaev, I. V.
This study concerns the influence of the boundary layer at an aircraft's fuselage, simulated by an infinite hard cylinder, on propeller noise in the acoustic far field. Also studied is the effect of the boundary layer on noise as a function of the thickness and profile of the mean velocity of the boundary layer, the Mach number of the incident flow, and the rotation speed of the propeller. It is shown that the boundary layer at the fuselage can substantially modify propeller noise in the far field and should therefore be taken into account in calculating community noise.
Turbulent boundary layers with large streamline curvature effects
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.
Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS
Fletcher, J. K.; Bretherton, Christopher S.; Xiao, Heng; Sun, Ruiyu N.; Han, J.
The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.
Coupling of magnetopause-boundary layer to the polar ionosphere
Wei, C.Q.; Lee, L.C. (Univ. of Alaska, Fairbanks (United States))
The authors develop a model which seeks to explain ultraviolet auroral images from the Viking satellite which show periodic bright regions which resemble [open quotes]beads[close quotes] or [open quotes]pearls[close quotes] aligned along the postnoon auroral oval. ULF geomagnetic pulsations observed in the cusp region are also addressed by this model. The model addresses plasma dynamics in the low-latitude boundary layer and interactions with the polar ionosphere by means of field-aligned current. The Kelvin-Helmholtz instability can develop in the presence of driven plasma flow, which can lead to the formation and growth of plasma vortices in the boundary layer. The finite conductivity of the earth ionosphere causes these vortices to decay. However regions of enhanced field-aligned power density in the postnoon auroral oval can be associated with field-aligned current filaments and boundary layer vortices. These structures may explain the observed bright spots. The authors also discuss the frequency spectrum and the polarization state of the pulsations.
Acoustic explorations of the upper ocean boundary layer
NASA Astrophysics Data System (ADS)
Vagle, Svein
The upper ocean boundary layer is an important but difficult to probe part of the ocean. A better understanding of small scale processes at the air-sea interface, including the vertical transfer of gases, heat, mass and momentum, are crucial to improving our understanding of the coupling between atmosphere and ocean. Also, this part of the ocean contains a significant part of the total biomass at all trophic levels and is therefore of great interest to researchers in a range of different fields. Innovative measurement plays a critical role in developing our understanding of the processes involved in the boundary layer, and the availability of low-cost, compact, digital signal processors and sonar technology in self-contained and cabled configurations has led to a number of exciting developments. This talk summarizes some recent explorations of this dynamic boundary layer using both active and passive acoustics. The resonant behavior of upper ocean bubbles combined with single and multi-frequency broad band active and passive devices are now giving us invaluable information on air-sea gas transfer, estimation of biological production, marine mammal behavior, wind speed and precipitation, surface and internal waves, turbulence, and acoustic communication in the surf zone.
Improving subtropical boundary layer cloudiness in the 2011 NCEP GFS
NASA Astrophysics Data System (ADS)
Fletcher, J. K.; Bretherton, C. S.; Xiao, H.; Sun, R.; Han, J.
The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of shortwave cloud radiative forcing, and affect predicted sea-surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parametrisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.
Improving subtropical boundary layer cloudiness in the 2011 NCEP GFS
NASA Astrophysics Data System (ADS)
Fletcher, J. K.; Bretherton, C. S.; Xiao, H.; Sun, R.; Han, J.
The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.
Review of Orbiter Flight Boundary Layer Transition Data
NASA Technical Reports Server (NTRS)
Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.
In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.
Aero-optic characteristics of turbulent compressible boundary layers
NASA Astrophysics Data System (ADS)
Wyckham, Christopher Mark
This dissertation presents a detailed study of the aberrating effect on a plane incident wavefront of light due to its passage through a turbulent, compressible boundary layer. This aberration has important implications for the design of airborne optical systems for imaging, communications, or projection. A Shack-Hartmann sensor and associated data analysis software suite were developed and validated for the high resolution measurement of two dimensional wavefront phase. Significant improvements in wavefront reconstruction were achieved by using the calculated centroid uncertainties to weight the least squares fitting of the phase surface. Using the Shack-Hartmann sensor in a high speed, one dimensional mode, individual structures are observed propagating past the sensor in a transonic flow. The uncertainties on the reconstructed phase in this mode are very high, however. In a two dimensional mode the uncertainties are greatly reduced and a large database of individual, uncorrelated wavefronts was collected, allowing statistics to be calculated such as the rms wavefront height and the Strehl ratio. Data were collected at transonic and hypersonic speeds and with no injection or with helium or nitrogen injection into the boundary layer. In all cases except the hypersonic helium injection case, the time averaged wavefronts reveal no features in the boundary layer which are steady in time. In the hypersonic helium injection case, however, steady, longitudinal features are observed, in agreement with previous observations. When helium is injected for window cooling at high speeds, the results show there may be an opportunity to reduce the resulting distortion by taking advantage of the stable structures that form in the boundary layer by using a low bandwidth adaptive optic system. A new scaling argument is also presented to allow the prediction and comparison of wavefront data for different compressible boundary layer flow conditions. The proposed formula gives promising results over a very wide range of Mach numbers and conditions when used to compare the current work as well as previous work by others, and may prove to be a crucial tool in the study of boundary layer aero-optic behavior.
The simulation of coherent structures in a laminar boundary layer
NASA Technical Reports Server (NTRS)
Breuer, Kenny; Landahl, Marten T.; Spalart, Philippe R.
Coherent structures in turbulent shear flows were studied extensively by several techniques, including the VITA technique which selects rapidly accelerating or decelerating regions in the flow. The evolution of a localized disturbance in a laminar boundary layer shows strong similarity to the evolution of coherent structures in a turbulent-wall bounded flow. Starting from a liftup-sweep motion, a strong shear layer develops which shares many of the features seen in conditionally-sampled turbulent velocity fields. The structure of the shear layer, Reynolds stress distribution, and wall pressure footprint are qualitatively the same, indicating that the dynamics responsible for the structure's evolution are simple mechanisms dependent only on the presence of a high mean shear and a wall and independent of the effects of local random fluctuations and outer flow effects. As the disturbance progressed, the development of streak-like-high- and low-speed regions associated with the three-dimensionality.
A Sensitivity Theory for the Equilibrium Boundary Layer Over Land
NASA Astrophysics Data System (ADS)
Cronin, T.
Due to the intrinsic complexities associated with modeling land-atmosphere interactions, global models typically use elaborate land surface and boundary layer physics parameterizations. Unfortunately, it is difficult to use elaborate models, by themselves, to develop a deeper understanding of how land surface parameters affect the coupled land-atmosphere system. At the same time, it is also increasingly important to gain a deeper understanding of the role of changes in land cover, land use, and ecosystem function as forcings and feedbacks in past and future climate change. Here, we outline the new framework of boundary layer climate sensitivity, which is based on surface energy balance, just as global climate sensitivity is based on top-of-atmosphere energy balance. We develop an analytic theory for the boundary layer climate sensitivity of an idealized model of a diurnally-averaged well-mixed boundary layer over land (Betts, 2000). This analytic sensitivity theory identifies changes in the properties of the land surface - including moisture availability, albedo, and aerodynamic roughness - as forcings, and identifies strong negative feedbacks associated with the surface fluxes of latent and sensible heat. We show that our theory can explain nearly all of the sensitivity of the Betts (2000) full system of equations, and find that nonlinear forcing functions are key to understanding changes in temperature caused by large changes in surface properties; this is directly analogous to the case of climate sensitivity, where nonlinear radiative forcing functions are key to understanding the response of global temperature to large changes in greenhouse gas concentrations. Favorable comparison of the theory and the simulation results from a two-column radiative convective model suggests that the theory may be broadly useful for unifying our understanding of how changes in land use or ecosystem function may affect climate change.
Control and reduction of unsteady pressure loads in separated shock wave turbulent boundary layer interaction
NASA Technical Reports Server (NTRS)
Dolling, David S.; Barter, John W.
The focus was on developing means of controlling and reducing unsteady pressure loads in separated shock wave turbulent boundary layer interactions. Section 1 describes how vortex generators can be used to effectively reduce loads in compression ramp interaction, while Section 2 focuses on the effects of 'boundary-layer separators' on the same interaction.
On single limits and the asymptotic behaviour of separating turbulent boundary layers
Daniel O. A. Cruz; Atila P. Silva Freire
The present work studies the asymptotic structure of the turbulent boundary layer near a separation point through the single limit concept of Kaplun. A new scaling procedure is introduced resulting in a changeable asymptotic structure which is consistent with the experimental data. The classical structure of the velocity and temperature boundary layers is shown to develop into a one-deck structure
A class of unsteady, three-dimensional flow structures in turbulent boundary layers
NASA Technical Reports Server (NTRS)
Ash, R. L.
A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary layer.
Analytical Solution for the Convectively-Mixed Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Ouwersloot, H. G.; Vil�-Guerau de Arellano, J.
Based on the prognostic equations of mixed-layer theory assuming a zeroth order jump at the entrainment zone, analytical solutions for the boundary-layer height evolution are derived with different degrees of accuracy. First, an exact implicit expression for the boundary-layer height for a situation without moisture is analytically derived without assuming any additional relationships or specific initial conditions. It is shown that to expand the solution to include moisture, only minor approximations have to be made. Second, for relatively large boundary-layer heights, the implicit representation is simplified to an explicit function. Third, a hybrid expression is proposed as a reasonable representation for the boundary-layer height evolution during the entire day. Subsequently, the analysis is extended to present the evolution of any boundary-layer averaged scalar, either inert or under idealized chemistry, as an analytical function of time and boundary-layer height. Finally, the analytical solutions are evaluated. This evaluation includes a sensitivity analysis of the boundary-layer height for the entrainment ratio, the free tropospheric lapse rate of the potential temperature, the time-integrated surface flux and the initial boundary-layer height and potential temperature jump.
Reconstruction of the surface impedance of an inhomogeneous planar boundary beyond layered media
Ali Yapar; Ibrahim Akduman
Determination of the boundary conditions of a surface from the remote field measurements is an important and interesting topic in the inverse scattering theory. As an example of such problems a method is developed for the reconstruction of the surface impedance of a planar boundary beyond a layered structure. The surface impedance is recovered from the boundary condition itself, which
Measurements of Instability and Transition in Hypersonic Boundary Layers
NASA Astrophysics Data System (ADS)
Casper, K. M.; Schneider, S. P.; Beresh, S. J.
Several studies on boundary-layer instability and transition have been conducted in the Boeing/AFOSR-Mach 6 Quiet Tunnel (BAM6QT) and the Sandia Hypersonic Wind Tunnels (HWT) at Mach 5 and 8. The first study looked at the effect of freestream noise on roughness- induced transition on a blunt cone. Temperature-sensitive paints were used to visualize the wake of an isolated roughness element at zero deg angle of attack in the BAM6QT. Transition was always delayed under quiet flow compared to noisy flow, even for an effective trip height. The second study measured transitional surface pressure fluctuations on a seven degree half-angle sharp cone in the HWT under noisy flow and in the BAM6QT under noisy and quiet flow. Fluctuations under laminar boundary layers reflected tunnel noise levels. Transition on the model only occurred under noisy flow, and fluctuations peaked during transition. Measurements of second- mode waves showed the waves started to grow under a laminar boundary layer, saturated, and then broke down near the peak in transitional pressure fluctuations. The third study looked at the development of wave packets and turbulent spots on the BAM6QT nozzle wall. A spark perturber was used to generate controlled disturbances. Measurements of the internal structure of the pressure field of the disturbances were made.
The cycling of sulfur dioxide in the marine boundary layer
Yvon, S.A.
The atmospheric cycling of sulfur dioxide (SO{sub 2}) is examined through the use of field measurements and photochemical modeling. A question exists as to whether or not SO{sub 2} is a major product of dimethylsulfide (DMS) oxidation and subsequently important in the formation of new particles and cloud condensation nuclei (CCN). The relative magnitudes of the different sources and sinks of SO{sub 2} in the remote marine boundary layer are looked at using field measurements of SO{sub 2}, DMS, and hydrogen sulfide (H{sub 2}S) and a time dependent photochemical box model of an air mass in the marine boundary layer. A new automated technique for measuring So{sub 2} was developed. It enables continuous real-time measurement of SO{sub 2} using HPLC/Fluorescence at parts-per-trillion levels. Atmospheric and seawater DMS and atmospheric H{sub 2}S were also measured during these cruises in order to definite the biogenic sources of SO{sub 2}. The observed SO{sub 2} levels in the marine boundary layer are much lower than those predicted by current photochemical models using the measured DMS concentrations. Also, current models predict that SO{sub 2} should have a pronounced diel cycle that is anticorrelated to that of DMS, however, there is no observable diel cycle in the SO{sub 2} data. Using a time-dependent photochemical box model and a model of the aqueous phase sea-salt aerosol chemistry, we examine the role of heterogeneous loss to sea-salt aerosols as a potentially important but previously unaccounted for sink for SO{sub 2} in the marine boundary layer. Our results indicate that this is a large sink for SO{sub 2} in this region.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S.; Spencer, Shelly Anne
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S. (Principal Investigator); Spencer, Shelly Anne
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-travelling, sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2(lambda)(sub TS)/pi, of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations and the Stokes wave subtracted) show the generation of 3-D-T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modelling are observed.
Helical circulations in the typhoon boundary layer Ryan Ellis1
Businger, Steven
., 2008]. Numerical studies include two-scale boundary layer models [Ginis et al., 2004] and 3-D idealized observations of Zhang et al. [2008] and the two-scale boundary layer model of Ginis et al. [2004]. Ginis et al. [2008]. This may help explain damage patterns observed by Fujita [1992] in hurricanes Andrew and Iniki
Reynolds number influences on turbulent boundary layer momentum transport
Paththage A. Priyadarshana
There are many engineering applications at Reynolds numbers orders of magnitude higher than existing turbulent boundary layer studies. Currently, the mechanisms for turbulent transport and the Reynolds number dependence of these mechanisms are not well understood. This dissertation presents Reynolds number influences on velocity and vorticity statistics, Reynolds shear stress, and velocity-vorticity correlations for turbulent boundary layers. Well resolved hot-wire
Sun-Earth connection: Boundary layer waves and auroras
G. S. Lakhina; B. T. Tsurutani; J. K. Arballo; C. Galvan
Boundary layers are the sites where energy and momentum are exchanged between two distinct plasmas. Boundary layers occurring in space plasmas can support a wide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond. The main characteristics of the broadband plasma waves (with frequencies > 1 Hz) observed in the magnetopause, polar
Experiments on the wind tunnel simulation of atmospheric boundary layers
Cesar Farell; Arun K. S. Iyengar
The simulation of atmospheric boundary layers using spires, a barrier wall, and a fetch of roughness elements is discussed in the light of experiments carried out to reproduce the characteristics of a boundary layer for urban terrain conditions. Comparisons of wind tunnel and atmospheric data are presented, including mean-velocity profiles, turbulence intensities, turbulence spectra, and turbulence length scales, in particular
Electromagnetic precipitation and ducting of particles in turbulent boundary layers
K. R. Davey; J. R. Melcher
A method for analyzing magnetic migration of particles in turbulent flows is applied to the prediction of particle trajectories and densities in turbulent aerodynamic boundary layers. Results for conditions typical of aircraft with 30-40 micron particles indicate a large upstream collection and a 5% loss of particles during one pass through the boundary layer. The capacity of the magnetic field
Some characteristics of turbulent boundary layers in rapidly accelerated flows
NASA Technical Reports Server (NTRS)
Brinich, P. F.; Neumann, H. E.
An analysis of time-mean-turbulent boundary layer velocity profiles measured in a rapidly accelerating flow suggests that the outer region of the velocity profiles consists of essentially inviscid, rotational flow. The extent of this inviscid outer region was observed in some cases to exceed 90 percent of what is ordinarily thought of as the turbulent boundary layer thickness. On the other hand, the inner frictional region of these velocity profiles appears to have turbulent characteristics similar to those of more conventional turbulent boundary layers. Hence, the outer edge boundary condition for this inner region is more properly the external rotational flow region than the free stream.
Direct numerical simulation of equilibrium turbulent boundary layers
NASA Technical Reports Server (NTRS)
Spalart, P. R.; Leonard, A.
This paper describes the simulation of turbulent boundary layers by direct numerical solution of the three-dimensional, time-dependent Navier-Stokes equations, using a spectral method. The flow is incompressible, with Re sub delta = 1000. The equations are written in the self-similar coordinate system and periodic streamwise and spanwise boundary conditions are imposed. A family of nine 'equilibrium' boundary layers, from the strongly accelerated 'sink' flow to Stratford's separating boundary layer is treated. Good general agreement with experiments is observed. The effects of pressure gradients on the structures and statistics, both in the wall and wake regions are discussed.
Turbulence modeling in shock wave/turbulent boundary layer interactions
NASA Technical Reports Server (NTRS)
Smits, A. J.
The research performed was an experimental program to help develop turbulence models for shock wave boundary layer interactions. The measurements were taken in a Mach 3, 16 deg compression corner interaction, at a unit Reynolds number of 63 x 10(exp 6)/m. The data consisted of heat transfer data taken upstream and downstream of the interaction, hot wire measurements of the instantaneous temperature and velocity fluctuations to verify the Strong Reynolds Analogy, and single- and double-pulsed Rayleigh scattering images to study the development of the instantaneous shock/turbulence interaction.
End-wall boundary layer prediction for axial compressors
NASA Technical Reports Server (NTRS)
Sockol, P. M.
An integral boundary layer procedure was developed for the computation of viscous and secondary flows along the annulus walls of an axial compressor. The procedure is an outgrowth and extension of the pitch-averaged methods of Mellor and Horlock. In the present work secondary flow theory is used to develop approximations for the velocity profiles inside a rotating blade row and for the blade force deficit terms in the momentum integral equations. The computer code based on this procedure was iteratively coupled to a quasi-one-dimensional model for the external inviscid flow. Computed results are compared with measurements in a compressor cascade.
Mixing dynamics within a turbid bottom boundary layer
NASA Astrophysics Data System (ADS)
Bastida, I.; Planella, J.; Roget, E.
Mixing dynamics within a turbid bottom boundary layer in a littoral zone of the Mediterranean Sea is analyzed. Data were taken in June 2004 with a free falling microstructure profiler. Mesoscale dynamics in the region was influenced by the outflow of the Ebre River and by the southwestern Catalan Current originating in the Gulf of Genoa. The magnitude of the near bottom current was 5-8 cm/s and the flow was affected by inertial oscillations. During the entire field campaign, the wind of ~ 6 m/s was from the northeast. The mean depth of the upper mixed layer was about 15 m, the thermocline occupied the depth range between 15 and 30 m, and the thickness of the turbid bottom boundary layer varied from 8 to 12 m. Different stations ranged from 15 to 60 m depth. Thorpe displacement, Th, was used to determine the turbulent patches and, in general, Thmax within the patches and the Thorpe scale, LTh, were found to be highly correlated and linearly dependent: Tmax= 2.6LTh. If Thmax and LTh were calculated at equidistant segments of the profiles, then Thmax ~ LTh0.85. Within the bottom layer turbulent patches were found to affect 35% of the total depth of the layer. The median size of the patches was 41 cm and their median buoyancy Reynolds number was 252. State of the turbulence within the bottom layer is discussed based on the turbulent Reynolds and the turbulent Froude numbers. According to the hydrodynamic diagram and the vertical profiles of the turbulent kinetic energy dissipation rate, different zones are identified, including an upper interface where Kelvin-Helmholtz instability develop. The different station-dependent structure of the turbidity profiles is related to the different mixing dynamics. Mean turbulent diffusivity of the turbid layer was obtained following the Osborn approach and found to be 2 x 10-5 m2/s.
Boundary Layer Perturbations Generated from small Oscillating Bumps
NASA Astrophysics Data System (ADS)
Gaster, Michael
Perturbations may be generated in a laminar boundary layer by various types of surface disturbance. Here we discuss the perturbations generted by the motion of a small piston mounted in the surface of a flat plate. Theoretical predictions of the flow field resulting from the periodic motion of the piston are made using the approximation that the steady base boundary layer is closely parallel and that the disturbance is sufficently small to warrant linearisation. These solutions are compared with measurements taken with a hot-wire anemometer of appropriate boundary layer experiments involving excitation by a piston of 2mm dia oscillating with amplitudes of 50 microns in a laminar boundary layer with a displacement thickness of 1mm. The Reynolds number of the boundary layer is roughly 1000 based on displacement thickness.
Destiny of earthward streaming plasma in the plasmasheet boundary layer
NASA Technical Reports Server (NTRS)
Green, J. L.; Horwitz, J. L.
The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.
The role of chemical boundary layers in regulating the thickness of continental and oceanic thermal boundary layers
Lee, Cin-Ty Aeolus
The role of chemical boundary layers in regulating the thickness of continental and oceanic thermal boundary layers Cin-Ty Aeolus Lee*, Adrian Lenardic, Catherine M. Cooper, Fenglin Niu, Alan Levander Department of Earth Science, MS-126, Rice University, 6100 Main St., Houston, TX 77005, United States
Integral method for the calculation of three-dimensional, laminar and turbulent boundary layers
NASA Technical Reports Server (NTRS)
Stock, H. W.
The method for turbulent flows is a further development of an existing method; profile families with two parameters and a lag entrainment method replace the simple entrainment method and power profiles with one parameter. The method for laminar flows is a new development. Moment of momentum equations were used for the solution of the problem, the profile families were derived from similar solutions of boundary layer equations. Laminar and turbulent flows at the wings were calculated. The influence of wing tapering on the boundary layer development was shown. The turbulent boundary layer for a revolution ellipsoid is calculated for 0 deg and 10 deg incidence angles.
Aerodynamic Models for Hurricanes III. Modeling hurricane boundary layer
Leonov, Arkady I
The third paper of the series (see previous ones in Refs.[1-2]) discusses basic physicalprocesses in the (quasi-) steady hurricane boundary layer (HBL), develops an approximate airflow model, establishes the HBL structure, and presents integral balance relations for dynamic and thermodynamic variables in HBL. Models of evaporation and condensation are developed, where the condensation is treated similarly to the slow combustion theory. A turbulent approximation for the lower sub-layer of HBL is applied to the sea-air interaction to establish the observed increase in angular momentum in the outer region of HBL.A closed set of balance relations has been obtained. Simple analytical solution of the set yields expressions for the basic dynamic variables - maximal tangential and radial velocities in hurricane, maximal vertical speed in eye wall, the affinity speed of hurricane travel, and the maximal temperature increase after condensation. Estimated values of the variables seem to be realistic. An attempt is also ...
Boundary Layer Rolls Observed Above and Below a Jet in a Marine Boundary Layer
NASA Astrophysics Data System (ADS)
Foster, R. C.; Emmitt, G. D.; Godwin, K.; Greco, S.
We have flown a coherent Doppler wind lidar (DWL) on the Cirpas Twin Otter off the California coast near Monterey since 2003. One scientific purpose of these flights is to understand the relationship between the turbulent fluxes measured on the aircraft or on other platforms and the observed structure of the marine boundary layer (MBL). Two common features are found in the MBL flow: (1) a strong jet at approximately 200 m above the sea surface; and (2) organized large eddies (OLE) in the form of roll vortices that are approximately aligned along the mean wind direction. On two flights (April 13, 2007 and September 30, 2012), the DWL data indicated that roll OLE existed simultaneously both above and below the jet. The DWL winds suggest that the OLE in these layers are sometimes independent and sometimes connected. Standard flux data are obtained on the Twin Otter at flight level, which is nominally 300 m. The 10 Hz wind and temperature data exhibit variability at spatial scales corresponding to the OLE wavelength. We have constructed a nonlinear theoretical model that includes triad wave-wave interactions to test the hypothesis that rolls could form both above and below the jet. This model shows that this is possible and that the rolls in the two layers could have unique characteristics compared to standard boundary layer rolls. The model further shows that the rolls above and below the jet are due to separate instabilities that interact. This is consistent with the observations of both connected and independent OLE above and below the jet. Contrast-enhanced DWL line-of-sight winds. Jet maximum 200 m below aircraft. Typical resonant triad solution for rolls above and below a PBL jet.
Computer program to calculate three-dimensional boundary layer flows over wings with wall mass transfer
NASA Technical Reports Server (NTRS)
Mclean, J. D.; Randall, J. L.
A system of computer programs for calculating three dimensional transonic flow over wings, including details of the three dimensional viscous boundary layer flow, was developed. The flow is calculated in two overlapping regions: an outer potential flow region, and a boundary layer region in which the first order, three dimensional boundary layer equations are numerically solved. A consistent matching of the two solutions is achieved iteratively, thus taking into account viscous-inviscid interaction. For the inviscid outer flow calculations, the Jameson-Caughey transonic wing program FLO 27 is used, and the boundary layer calculations are performed by a finite difference boundary layer prediction program. Interface programs provide communication between the two basic flow analysis programs. Computed results are presented for the NASA F8 research wing, both with and without distributed surface suction.
A combined model for improving estimation of atmospheric boundary layer height
NASA Astrophysics Data System (ADS)
Bachtiar, V. S.; Davies, F.; Danson, F. M.
Atmospheric boundary layer height is one of the most important parameters in atmospheric dispersion modelling because it has a large effect on predicted air quality. Comparisons between Atmospheric Dispersion Modelling System, version 4 (ADMS 4) and lidar data were carried out on boundary layer height data from central London. The comparison showed that the boundary layer height predicted by the ADMS 4 was, on average, lower than lidar for the subset of data taken. ADMS 4 has a very simple surface scheme which is not representative of complex urban environments and the results from this research imply that there is not sufficient surface roughness within the model to produce a large enough boundary layer height. The aim of this study is to create an improved model to better forecast the growth of the daytime urban boundary layer and predict boundary layer height, h, in an air quality dispersion model using lidar measurements. The combined model was developed by using a surface model and an atmospheric boundary layer height model. Measurements of atmospheric boundary layer height by lidar used vertical velocity variance and the overall conclusion was that the combined model improved the performance of ADMS in urban areas.
Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M., E-mail: email@example.com [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)
The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification of three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.
Turbulence intensity similarity laws for high Reynolds number boundary layers
Gary Kunkel; Ivan Marusic
Data obtained in the surface layer of the atmospheric boundary layer at the SLTEST (Surface Layer Turbulence and Environmental Science Test) facility located on the western Utah salt flats are used to analyze current turbulence intensity similarity laws. The high Reynolds number data are shown to be consistent with the Marusic, Uddin and Perry (Phys. Fluids 1997) formulation which applies
Titan's planetary boundary layer structure at the Huygens landing site
Tetsuya Tokano; Francesca Ferri; Giacomo Colombatti; Teemu M�kinen; Marcello Fulchignoni
Huygens Atmospheric Structure Instrument (HASI) for the first time performed an in situ measurement of the thermal structure in Titan's atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer (PBL). The vertical potential temperature profile reveals the presence of a weakly convective PBL, with a surface layer thickness of 10 m and an outer layer with a
Characteristics of vortex packets in a boundary layer
Bharathram Ganapathisubramani; Ellen Longmire; Ivan Marusic
Stereo PIV was used to measure all three velocity components in streamwise-spanwise (x-y) planes of a turbulent boundary layer at Re_tau = 1060. Datasets were obtained in the log layer and beyond. The vector fields in the log layer (z^+ = 92 and 150, z - wall normal direction) revealed signatures of vortex packets similar to those found by Adrian
Development of a defect stream function, law of the wall/wake method for compressible turbulent boundary layers. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Wahls, Richard A.
The method presented is designed to improve the accuracy and computational efficiency of existing numerical methods for the solution of flows with compressible turbulent boundary layers. A compressible defect stream function formulation of the governing equations assuming an arbitrary turbulence model is derived. This formulation is advantageous because it has a constrained zero-order approximation with respect to the wall shear stress and the tangential momentum equation has a first integral. Previous problems with this type of formulation near the wall are eliminated by using empirically based analytic expressions to define the flow near the wall. The van Driest law of the wall for velocity and the modified Crocco temperature-velocity relationship are used. The associated compressible law of the wake is determined and it extends the valid range of the analytical expressions beyond the logarithmic region of the boundary layer. The need for an inner-region eddy viscosity model is completely avoided. The near-wall analytic expressions are patched to numerically computed outer region solutions at a point determined during the computation. A new boundary condition on the normal derivative of the tangential velocity at the surface is presented; this condition replaces the no-slip condition and enables numerical integration to the surface with a relatively coarse grid using only an outer region turbulence model. The method was evaluated for incompressible and compressible equilibrium flows and was implemented into an existing Navier-Stokes code using the assumption of local equilibrium flow with respect to the patching. The method has proven to be accurate and efficient.
Influences on the Height of the Stable Boundary Layer as seen in LES
Kosovic, B; Lundquist, J
Climate models, numerical weather prediction (NWP) models, and atmospheric dispersion models often rely on parameterizations of planetary boundary layer height. In the case of a stable boundary layer, errors in boundary layer height estimation can result in gross errors in boundary-layer evolution and in prediction of turbulent mixing within the boundary layer.
Infrared Imaging of Boundary Layer Transition Flight Experiments
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J., Jr.; Schwartz, Richard; Ross, Martin; Anderson, Brian; Campbell, Charles H.
The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASA-sponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.
Boundary layer receptivity to convected gusts and sound
NASA Astrophysics Data System (ADS)
Parekh, D. E.; Pulvin, P.; Wlezien, R. W.
The receptivity of a laminar boundary layer to sound and convected gusts is examined experimentally, considering the coupling between these external disturbances and the boundary layer in the vicinity of a 24:1 elliptic leading edge, a porous strip, and a forward-facing step. A conventional loudspeaker generates the acoustic disturbance, and an array of oscillating ribbons produces a vortical disturbance in the form of a periodic convected gust. Techniques for decoupling the excitation from the boundary layer response and comparisons of receptivity mechanisms are discussed.
Nonlinear spatial evolution of inviscid instabilities on hypersonic boundary layers
NASA Technical Reports Server (NTRS)
Wundrow, David W.
The spatial development of an initially linear vorticity-mode instability on a compressible flat-plate boundary layer is considered. The analysis is done in the framework of the hypersonic limit where the free-stream Mach number M approaches infinity. Nonlinearity is shown to become important locally, in a thin critical layer, when sigma, the deviation of the phase speed from unity, becomes o(M(exp -8/7)) and the magnitude of the pressure fluctuations becomes 0(sigma(exp 5/2)M(exp 2)). The unsteady flow outside the critical layer takes the form of a linear instability wave but with its amplitude completely determined by the nonlinear flow within the critical layer. The coupled set of equations which govern the critical-layer dynamics reflect a balance between spatial-evolution, (linear and nonlinear) convection and nonlinear vorticity-generation terms. The numerical solution to these equations shows that nonlinear effects produce a dramatic reduction in the instability-wave amplitude.
Characteristics of vortex packets in a boundary layer
NASA Astrophysics Data System (ADS)
Ganapathisubramani, Bharathram; Longmire, Ellen; Marusic, Ivan
Stereo PIV was used to measure all three velocity components in streamwise-spanwise (x-y) planes of a turbulent boundary layer at Re_? = 1060. Datasets were obtained in the log layer and beyond. The vector fields in the log layer (z^+ = 92 and 150, z - wall normal direction) revealed signatures of vortex packets similar to those found by Adrian and co-workers in their PIV experiments. Groups of legs of hairpin vortices appeared to be coherently arranged along the x direction. These regions also generated substantial Reynolds shear stress (-uw), sometimes as high as 40U_?^2. A feature extraction algorithm was developed to automate the identification and characterization of these packets of hairpin vortices. Identified patches contributed 28% to the total -uw while occupying less than 5% of the total area in the log layer. Beyond the log layer (z^+ = 198, 530), the spatial organization into packets breaks down. Instead, large individual vortex cores and spanwise strips of positive and negative wall-normal velocity were observed. Supported by NSF (ACI-9982774, CTS-9983933).
Boundary Layer Balloons : New concepts for new missions
NASA Astrophysics Data System (ADS)
Verdier, Nicolas
Using balloons is a good way to study and understand atmospheric and oceanic phenomena which make the earth climate. Nevertheless, large deployment is today limited by safety for heavy balloons. In the atmospheric boundary layer using heavy balloons increase the risk for population and aircrafts. Based on recent technology improvements, a new balloon concept, Nano Aerostat Network for Observations (NANO), is developed by CNES in order to offer a panel from local to global scale atmospheric studies in the planetary boundary layer. Miniaturized Instrumentation has been developed specifically for these balloons to offer opportunities to measure static and dynamic atmospheric parameters like pressure, temperature, moisture, wind and radiations. Nevertheless, the main challenge was to collect and transfer local data from balloons to ground stations farther than radioelectric line of sight during long duration flight and saving weight. For a few hundred grams payload it is impossible to use satellite communication system but only specific telemetry concept. Then, CNES imagine deploying many balloons to make a network where each gondola should be a node. A specific routing protocol for instruments measurements by bouncing data on each balloon was developed, simulated and tested. Now, we plan to use NANO concept to sample with high spatial and temporal resolution High-impact weather events during HYMEX/BAMED and DSCT campaigns (2011).
Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions
NASA Astrophysics Data System (ADS)
Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa
Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.
Computation of turbulent boundary layers on curved surfaces, 1 June 1975 - 31 January 1976
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
An accurate method was developed for predicting effects of streamline curvature and coordinate system rotation on turbulent boundary layers. A new two-equation model of turbulence was developed which serves as the basis of the study. In developing the new model, physical reasoning is combined with singular perturbation methods to develop a rational, physically-based set of equations which are, on the one hand, as accurate as mixing-length theory for equilibrium boundary layers and, on the other hand, suitable for computing effects of curvature and rotation. The equations are solved numerically for several boundary layer flows over plane and curved surfaces. For incompressible boundary layers, results of the computations are generally within 10% of corresponding experimental data. Somewhat larger discrepancies are noted for compressible applications.
Application of a general boundary layer analysis to turbulent boundary layers subjected to strong favorable pressure gradients
NASA Technical Reports Server (NTRS)
Kreskovsky, J. P.; Shamroth, S. J.; Mcdonald, H.
Theoretical predictions of turbulent boundary layer development under the influence of strong favorable pressure gradients made using a finite-difference calculation procedure are compared to experimental data. Comparisons are presented for low speed flows with and without wall heat transfer as well as for supersonic flows with adiabatic walls. The turbulence model used is governed by an integral form of the turbulence kinetic energy equation and the results are compared with predictions made using a conventional equilibrium turbulence model based upon Prandtl's mixing length, a Clauser-type eddy viscosity model used by Cebecci and Mosinskis, and a two-equation turbulence energy model of Launder and Jones.
Boundary layer modification by means of wall suction and the effect on the wake behind a rectangular forebody
NASA Astrophysics Data System (ADS)
Trip, Renzo; Fransson, Jens H. M.
The wake characteristics of a two-dimensional rectangular forebody with a smooth leading edge and a blunt trailing edge are investigated. Wall suction is applied along the forebody in order to modify the developing boundary layer. An initially laminar boundary layer subject to suction yields an asymptotic suction boundary layer at the trailing edge of the body, whereas a high enough suction coefficient relaminarizes an initially turbulent boundary layer. The critical suction velocity required to achieve this significant modification of the boundary layer properties is typically in the order of 1% of the free-stream velocity, where the critical suction coefficient depends on the Reynolds number. We show that a thinner boundary layer induces a higher vortex shedding frequency and a lower base pressure. Furthermore, the boundary layer state, laminar or turbulent, has a significant influence on the wake. For example, the Strouhal number based on the effective body thickness is being reduced by 25% from laminar to turbulent inlet conditions.
Stability of the laminar boundary layer in a streamwise corner
NASA Astrophysics Data System (ADS)
Lakin, W. D.; Hussaini, M. Y.
The stability of viscous, incompressible flow along a streamwise corner, often called the corner boundary layer problem is examined. The semi-infinite boundary value problem satisfied by small amplitude disturbances in the 'bending boundary layer' region is obtained. The mean secondary flow induced by the corner exhibits a flow reversal in this region. Uniformly valid 'first approximations' to solutions of the governing differential equations are derived. Uniformity at infinity is achieved by a suitable choice of the large parameter and use of an approximate Langer variable. Approximations to solutions of balanced type have a phase shift across the critical layer which is associated with instabilities in the case of two dimensional boundary layer profiles. Previously announced in STAR as N84-17532
Mathematical models of momentum transfer in the boundary layer
NASA Astrophysics Data System (ADS)
Laptev, A. G.; Farakhov, T. M.
Consideration has been given to the processes of momentum transfer in the laminar and turbulent boundary layers on a plate and in a tube. Original models for calculation of the tangential stress, friction factors, boundary-layer thickness, and coefficients of momentum transfer in the boundary layers on a plate and in a tube have been obtained under different conditions of motion of the gas medium. Examples of calculation of the indicated characteristics have been given; the results obtained have been compared to the existing experimental data. The obtained equations and methods of determination of the characteristics of the boundary layer can be used in designing industrial heat- and mass-exchange apparatuses of various structures and other equipment.
Control and Identification of Turbulent Boundary Layer Separation
NASA Technical Reports Server (NTRS)
Seifert, Avi; Pack-Melton, La Tunia
Effective delay of turbulent boundary layer separation could be achieved via closed-loop control. Constructing such a system requires that sensor data be processed, real-time, and fed into the controller to determine the output. Current methods for detection of turbulent boundary layer separation are lacking the capability of localized, fast and reliable identification of the boundary layer state. A method is proposed for short-time FFT processing of time series, measured by hot-film sensors, with the purpose of identifying the alternation of the balance between small and large scales as the boundary layer separates, favoring the large scales. The method has been validated by comparison to other criteria of separation detection and over a range of baseline and controlled flow conditions on a simplified high-lift system, incorporating active flow control.
Stability of the laminar boundary layer in a streamwise corner
NASA Technical Reports Server (NTRS)
Lakin, W. D.
The stability of viscous, incompressible flow along a streamwise corner, often called the corner boundary layer problem is examined. The semi-infinite boundary value problem satisfied by small amplitude disturbances in the "bending boundary layer' region is obtained. The mean secondary flow induced by the corner exhibits a flow reversal in this region. Uniformly valid "first approximations' to solutions of the governing differential equations are derived. Uniformity at infinity is achieved by a suitable choice of the large parameter and use of an approximate Langer variable. Approximations to solutions of balanced type have a phase shift across the critical layer which is associated with instabilities in the case of two dimensional boundary layer profiles.
Performance of a boundary layer ingesting propulsion system
Plas, Ang�lique (Ang�lique Pascale)
This thesis presents an assessment of the aerodynamic performance of an aircraft propulsion system, with embedded engines, in the presence of aircraft fuselage boundary layer ingestion (BLI). The emphasis is on defining ...
Distributed Roughness Receptivity in a Flat Plate Boundary Layer
Kuester, Matthew Scott
manufactured using rapid prototyping and installed flush with the wall in a flat plate boundary layer. The main objective was to compare the wakes of the discrete roughness and the combined roughness to examine if the distributed roughness shields...
Investigation of the Stable Atmospheric Boundary Layer at Halley Antarctica
NASA Astrophysics Data System (ADS)
Rodrigo, Javier Sanz; Anderson, Philip S.
Boundary-layer measurements from the Brunt Ice Shelf, Antarctica are analyzed to determine flux-profile relationships. Dimensionless quantities are derived in the standard approach from estimates of wind shear, potential temperature gradient, Richardson number, eddy diffusivities for momentum and heat, Prandtl number, mixing length and turbulent kinetic energy. Nieuwstadt local scaling theory for the stable atmospheric boundary-layer appears to work well departing only slightly from expressions found in mid-latitudes. An - single-column model of the stable boundary layer is implemented based on local scaling arguments. Simulations based on the first GEWEX Atmospheric Boundary-Layer Study case study are validated against ensemble-averaged profiles for various stability classes. A stability-dependent function of the dimensionless turbulent kinetic energy allows a better fit to the ensemble profiles.
Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number
Semper, Michael Thomas
The purpose of the current study was to answer several questions related to hypersonic, low Reynolds number, turbulent boundary layers, of which available data related to turbulence quantities is scarce. To that end, a unique research facility...
Characteristic scaling parameters in the planetary boundary layer have been applied to estimate the dispersion of nonbuoyant gaseous pollutants. Vertical and lateral spread are treated separately, and the choice of parameters for the dispersion models depends upon the actual stat...
Fast and accurate metrology of multi-layered ceramic materials by an automated boundary detection algorithm developed for optical coherence tomography data
Ekberg, Peter; Su, Rong; Chang, Ernest W.; Yun, Seok Hyun; Mattsson, Lars
Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 �m when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness. PMID:24562018
Effect of Protuberance Shape and Orientation on Space Shuttle Orbiter Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
King, RUdolph A.; Berry, Scott A.; Kegerise, Michael A.
This document describes an experimental study conducted to examine the effects of protuberances on hypersonic boundary-layer transition. The experiment was conducted in the Langley 20-Inch Mach 6 Tunnel on a series of 0.9%-scale Shuttle Orbiter models. The data were acquired to complement the existing ground-based boundary-layer transition database that was used to develop Version 1.0 of the boundary-layer transition RTF (return-to-flight) tool. The existing ground-based data were all acquired on 0.75%-scale Orbiter models using diamond-shaped ( pizza-box ) trips. The larger model scale facilitated in manufacturing higher fidelity protuberances. The end use of this experimental database will be to develop a technical basis (in the form of a boundary-layer transition correlation) to assess representative protrusion shapes, e.g., gap fillers and protrusions resulting from possible tile repair concepts. The primary objective of this study is to investigate the effects of protuberance-trip location and geometry on Shuttle Orbiter boundary-layer transition. Secondary goals are to assess the effects of gap-filler orientation and other protrusion shapes on boundary-layer transition. Global heat-transfer images using phosphor thermography of the Orbiter windward surface and the corresponding streamwise and spanwise heating distributions were used to infer the state of the boundary layer, i.e., laminar, transitional, or turbulent.
Turbulent oceanic western-boundary layers at low latitude
NASA Astrophysics Data System (ADS)
Quam Cyrille Akuetevi, Cataria; Wirth, Achim
Low latitude oceanic western-boundary layers range within the most turbulent regions in the worlds ocean. The Somali current system with the Great Whirl and the Brazilian current system with its eddy shedding are the most prominent examples. Results from analytical calculations and integration of a one layer reduced-gravity fine resolution shallow water model is used to entangle this turbulent dynamics. Two types of wind-forcing are applied: a remote Trade wind forcing with maximum shear along the equator and a local Monsoon wind forcing with maximum shear in the vicinity of the boundary. For high values of the viscosity (> 1000m2s-1) the stationary solutions compare well to analytical predictions using Munk and inertial layer theory. When lowering the friction parameter time dependence results. The onset of instability is strongly influenced by inertial effects. The unstable boundary current proceeds as a succession of anti-cyclonic coherent eddies performing a chaotic dynamics in a turbulent flow. The dynamics is governed by the turbulent fluxes of mass and momentum. We determine these fluxes by analyzing the (potential) vorticity dynamics. We demonstrate that the boundary-layer can be separated in four sub-layers, which are (starting from the boundary): (1) the viscous sub-layer (2) the turbulent buffer-layer (3) the layer containing the coherent structures and (4) the extended boundary layer. The characteristics of each sub-layer and the corresponding turbulent fluxes are determined, as are the dependence on latitude and the type of forcing. A new pragmatic method of determining the eddy viscosity, based on Munk-layer theory, is proposed. Results are compared to observations and solutions of the multi-level primitive equation model (DRAKKAR).
Numerical solutions for unsteady laminar boundary layers behind blast waves
NASA Astrophysics Data System (ADS)
Liu, S. W.; Mirels, H.
The paper presents the similarity solutions obtained for laminar boundary layers behind a power-law shock associated with a blast wave. A finite-difference method based on Blottner's numerical scheme (1970) is used. The results are valid, at all times, in the entire flow region between the shock front and the immediate vicinity of the blast-wave origin provided the boundary layer remains laminar.
Benthic boundary layer processes in the Lower Florida Keys
D. L. Lavoie; M. D. Richardson; C. Holmes
This special issue of Geo-Marine Letters, �Benthic Boundary Layer Processes in the Lower Florida Keys,� includes 12 papers that present preliminary results from the\\u000a Key West Campaign. The Dry Tortugas and Marquesas Keys test sites were selected by a group of 115 scientists and technicians\\u000a to study benthic boundary layer processes in a carbonate environment controlled by bioturbation and biogeochemical
Report of secondary flows, boundary layers, turbulence and wave team
NASA Technical Reports Server (NTRS)
Doviak, R.
Correspondence concerning the comparison of horizontal wind fields, two dimensional spectra, heat flux, mesoscale divergence and deformation in the prestorm environment, and thunderstorm gust front winds is presented. Other subjects include the use of radar to determine heating rate and evaporation near the Earth's surface for an unstable boundary layer and statistical considerations in the estimation of wind fields from single Doppler radar and application to prestorm boundary layer observations.
Sun-Earth connection: Boundary layer waves and auroras
G S Lakhina; B T Tsurutani; J K Arballo; C Galvan
Boundary layers are the sites where energy and momentum are exchanged between two distinct plasmas. Boundary layers occurring\\u000a in space plasmas can support a wide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond.\\u000a The main characteristics of the broadband plasma waves (with frequencies >1 Hz) observed in the magnetopause, polar cap,
Spectral stability of Prandtl boundary layers: an overview
Emmanuel Grenier; Yan Guo; Toan T. Nguyen
In this paper we show how the stability of Prandtl boundary layers is linked to the stability of shear flows in the incompressible Navier Stokes equations. We then recall classical physical instability results, and give a short educational presentation of the construction of unstable modes for Orr Sommerfeld equations. We end the paper with a conjecture concerning the validity of Prandtl boundary layer asymptotic expansions.
Reynolds Stress Budgets in Couette and Boundary Layer Flows
Jukka Komminaho; Martin Skote
Reynolds stress budgets for both Couette and boundary layer flows are evaluated and presented. Data are taken from direct\\u000a numerical simulations of rotating and non-rotating plane turbulent Couette flow and turbulent boundary layer with and without\\u000a adverse pressure gradient. Comparison of the total shear stress for the two types of flows suggests that the Couette case\\u000a may be regarded as
Approximation theory for boundary layer suction through individual slits
NASA Technical Reports Server (NTRS)
Walz, A.
The basic concepts of influencing boundary layers are summarized, especially the prevention of flow detachment and the reduction of frictional resistance. A mathematical analysis of suction through a slit is presented with two parameters, for thickness and for shape of the boundary layer, being introduced to specify the flow's velocity profile behind the slit. An approximation of the shape parameter produces a useful formula, which can be used to determine the most favorable position of the slit. An aerodynamic example is given.
Separating and turbulent boundary layer calculations using polynomial interpretation
NASA Technical Reports Server (NTRS)
Rubin, S. G.; Rivera, S.
Higher order numerical methods derived from polynomial spline interpolation or Hermitian differencing are applied to a separating laminar boundary layer, i.e., the Howarth problem, and the turbulent flat plate boundary layer flow. Preliminary results are presented. It is found that accuracy equal to that of conventional second order accurate finite difference methods is achieved with many fewer mesh points and with reduced computer storage and time requirements.
Cross-equatorial and boundary layer exchange: A FGGE review
NASA Technical Reports Server (NTRS)
Young, J. A.
The Global Weather Experiment (FGGE) provided unique data on the interesting phenomenon of cross-equatorial flow. Such motion is a key element of the seasonal cycle of the tropics, especially in monsoonal regions. The IIb obserations, IIIb assimilations, and implied dynamics of the flows are reviewed. Additional emphasis is given to the low level branches concentrated in the planetary boundary layer, including air sea interaction and vertical turbulence processes. The results of a recent MONEX Boundary Layer Workshop are summarized.
Interaction of a Boundary Layer with a Turbulent Wake
NASA Technical Reports Server (NTRS)
Piomelli, Ugo
The objective of this grant was to study the transition mechanisms on a flat-plate boundary layer interacting with the wake of a bluff body. This is a simplified configuration presented and designed to exemplify the phenomena that occur in multi-element airfoils, in which the wake of an upstream element impinges on a downstream one. Some experimental data is available for this configuration at various Reynolds numbers. The first task carried out was the implementation and validation of the immersed-boundary method. This was achieved by performing calculations of the flow over a cylinder at low and moderate Reynolds numbers. The low-Reynolds number results are discussed, which is enclosed as Appendix A. The high-Reynolds number results are presented in a paper in preparation for the Journal of Fluid Mechanics. We performed calculations of the wake-boundary-layer interaction at two Reynolds numbers, Re approximately equal to 385 and 1155. The first case is discussed and a comparison of the two calculations is reported. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. This is shown: long streaky structures appear in the boundary layer in correspondence of the three-dimensionalities in the rollers. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established. A third simulation was subsequently carried out at a higher Reynolds number, Re=3900. This calculation gave results similar to those of the Re=l155 case. Turbulence was established at fairly low Reynolds number, as a consequence of the high level of the free-stream perturbation. An instantaneous flow visualization for that case is shown. A detailed examination of flow statistics in the transitional and turbulent regions, including the evolution of the turbulent kinetic energy (TKE) budget and frequency spectra showed the formation and evolution of turbulent spots characteristic of the bypass transition mechanism. It was also observed that the turbulent eddies achieved an equilibrium, fully developed turbulent states first, as evidenced by the early agreement achieved by the terms in the TKE budget with those observed in turbulent flows. Once a turbulent Reynolds stress profile had been established, the velocity profile began to resemble a turbulent one, first in the inner region and later in the outer region of the wall layer. An extensive comparison of the three cases, including budgets, mean velocity and Reynolds stress profiles and flow visualization, is included. The results obtained are also presented.
Stability of three-dimensional supersonic boundary layers
NASA Astrophysics Data System (ADS)
Balakumar, Ponnampalam; Reed, Helen L.
A rotating cone that is located in a supersonic free stream at zero angle of attack is used as a model to investigate the stability of three-dimensional supersonic boundary layers. The boundary-layer profiles on the surface are calculated using the Cebeci-Keller box scheme. The stability equations are solved to determine the eigenvalues using a two-point fourth-order finite-difference scheme [Malik et al., Z. Angew. Math. Phys. 33, 189 (1982)]. The results show that the amplification rate of the first mode is increased by a factor of 2 to 4 due to the cross-flow, compared with a two-dimensional flow with the same streamwise profile. This increase decreases with increasing Mach number. The instability with cross-flow covers a wide range of unstable frequencies (including zero) and wave numbers. The results also show that the second mode in a three-dimensional boundary layer is oblique whereas the second mode in a two-dimensional boundary layer is two dimensional. The maximum amplification rate of the second mode decreases more slowly with increasing wave angle in a three-dimensional boundary layer than in a two-dimensional boundary layer. It is concluded that the cross-flow instability becomes important for cross-flow Reynolds number on the order of 50 for low Mach numbers and 100 for high Mach numbers, this Reynolds number range corresponds to a maximum cross-flow velocity of about 4%.
Turbulent boundary layer in high Rayleigh number convection in air.
du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, Andr�; Willert, Christian
Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-B�nard experiment are presented for the Rayleigh number Ra=1.4�1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re?200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-B�nard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal. PMID:24724653
Critical Averaging Time for Atmospheric Boundary Layer Fluxes
NASA Astrophysics Data System (ADS)
Holmes, H.
Calculation of heat and momentum fluxes in the Atmospheric Boundary Layer (ABL) requires separating the turbulent signal into mean and fluctuating components. Since the ABL is not statistically stationary, separation of these components depends on the inherent scales of motion in the flow. A new method is presented that utilizes energy spectra and cospectra analyses of raw velocity and temperature signals to select a critical averaging time, tc, for calculating the unsteady mean components of those signals. The new method is applied to high quality sonic anemometry data acquired at the Surface Layer Turbulence and Environmental Science Test (SLTEST) Facility located in Utah's western desert. Results for the unstable boundary layer show a correlation between tc and the characteristic time scale based on the ratio of mixed layer depth and convective velocity. Extension of the new method toward selection of a critical averaging time appropriate for the near-neutral boundary layer will also be discussed.
Modelling Unsteady Wall Pressures Beneath Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Ahn, B-K.; Graham, W. R.; Rizzi, S. A.
As a structural entity of turbulence, hairpin vortices are believed to play a major role in developing and sustaining the turbulence process in the near wall region of turbulent boundary layers and may be regarded as the simplest conceptual model that can account for the essential features of the wall pressure fluctuations. In this work we focus on fully developed typical hairpin vortices and estimate the associated surface pressure distributions and their corresponding spectra. On the basis of the attached eddy model, we develop a representation of the overall surface pressure spectra in terms of the eddy size distribution. Instantaneous wavenumber spectra and spatial correlations are readily derivable from this representation. The model is validated by comparison of predicted wavenumber spectra and cross-correlations with existing emperical models and experimental data.
Lidar-based remote sensing of atmospheric boundary layer height over land and ocean
NASA Astrophysics Data System (ADS)
Luo, T.; Yuan, R.; Wang, Z.
Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of the ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and the ABL vertical structure over ocean and land are analyzed. The new methods are then applied to satellite lidar measurements. The aerosol-derived global marine boundary layer heights are evaluated with marine ABL stratiform cloud top heights and results show a good agreement between them.
Establishment of a research facility for investigating the effects of unsteady inlet flow, pressure gradient and curvature on boundary layer development, wake development and heat transfer
Pardivala, Darayus Noshir
Development, Wake Darayus Noshir Pardivala, B. S. , Texas A&M University Development and Heat Transfer. (December 1991) Chair of Advisory Committee: Dr. -Ing. Taher Schobeiri A unique test facility has been developed to systematically study the influence... father Noshir M. Pardivala, whose love and support have made it possible for me to attain my goals. ACKNOWLEDGEMENTS The author would like to thank Dr. -Ing. Taher Schobeiri for the opportunity to work on this project. His extraordinary dedication...
Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code
NASA Technical Reports Server (NTRS)
Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.
The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.
Atmospheric Boundary Layer (ABL) Spring 2013
in the Atmosphere · Chandrasekahr (1961) Hydrodynamic and Hydromagnetic Stability · Garratt (1992) The Atmospheric] · Ekman layer · Turbulent Kinetic Energy equation [Ch. 5] · Flow Stability (Richardson No.) [Ch. 5
Clouds, Precipitation and Marine Boundary Layer Structure during MAGIC (Invited)
NASA Astrophysics Data System (ADS)
Kollias, P.; Zhou, X.; Lewis, E. R.
Marine boundary layer clouds in the subtropics play a key role in cloud-climate feedbacks that are poorly understood and are key elements in biases in seasonally coupled model forecasts and simulated mean climate. In particular, the representation of the transition from the stratocumulus (Sc) regime, to shallow cumulus (Cu) underlines one of the most challenging problems to the modeling community In MAGIC, the Marine ARM (Atmospheric Radiation Measurement) GPCI (Global Energy and Water Cycle Experiment [GEWEX] Cloud System Studies [GCSS] Pacific Cross-section Intercomparison) Investigation of Clouds study the second Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF2) during the Marine ARM GPCI Investigation of Clouds (MAGIC) provided an unparalleled dataset to study the statistical properties of MBL clouds and the transitions between Sc and Cu. Utilizing AMF2, we develop an objective scheme to identify MBL cloud occurrence across each leg and to recognize some important properties of different MBL cloud (e.g. Sc and Cu) and precipitation types. The variability and frequency of occurrence of the different cloud and precipitation events is presented with emphasis on the various MBL cloud structures. A statistical analysis of macroscopic properties (e.g. Inversion and transition layer) and cloud structure (e.g. cloud boundaries) is preformed relating to the thermodynamic profiles. Further emphasis is placed on the differentiation between Cu and Sc regimes as well as the presence of decoupling.
Demonstration of a laser vorticity probe in turbulent boundary layers
Su, W-J.; Stepaniuk, V.; Oetuegen, M. V. [Aeroballistics Division, U.S. Army Armament Research, Development and Engineering Center, Picatinny Arsenal, New Jersey 07806 (United States); Lenterra, Inc., West Orange, New Jersey 07052 (United States); Mechanical Engineering Department, Southern Methodist University, Dallas, Texas 75275 (United States)
A laser-based probe for the nonintrusive measurement of velocity gradient and vorticity was demonstrated in turbulent boundary layers. Unlike most other optical methods, the current technique provides an estimate of the velocity gradient, without having to first measure velocity at multiple points. The measurement principle is based on the heterodyne of coherent light scattered from two adjacent particles. The beat frequency of the heterodyne is directly proportional to the velocity gradient. The probe is assembled from commercially available, inexpensive optical components. A laser Doppler velocimeter (LDV) processor is used to analyze the heterodyne signal. A component of vorticity is obtained by using two appropriately aligned velocity gradient probes. The optical probes developed were used in turbulent boundary layers to measure local, time-frozen velocity gradients {partial_derivative}u/{partial_derivative}y, {partial_derivative}v/{partial_derivative}x, and {partial_derivative}v/{partial_derivative}y, as well as the spanwise vorticity. The measurements were compared to those inferred from LDV measurements in the same facility and to data available in the literature.
A top specified boundary layer (TSBL) approximation approach for the simulation of groundwater contamination processes
Rubin, H.; Buddemeier, R.W.
This paper presents improvements in the 'classical boundary layer' (CBL) approximation method to obtain simple but robust initial characterization of aquifer contamination processes. Contaminants are considered to penetrate into the groundwater through the free surface of the aquifer. The improved method developed in this study is termed the 'top specified boundary layer' (TSBL) approach. It involves the specification of the contaminant concentration at the top of the contaminated 'region of interest' (ROI), which is simulated as a boundary layer. the TSBL modification significantly improves the ability of the boundary layer method to predict the development of concentration profiles over both space and time. The TSBL method can be useful for the simulation of cases in which the contaminant concentration is prescribed at the aquifer's free surface as well as for cases in which the contaminant mass flux is prescribed at the surface.
Turbulence in a Convective Marine Atmospheric Boundary Layer
Shu-Hsien Chou; David Atlas; Eueng-Nan Yeh
The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found
Basic entrainment equations for the atmospheric boundary layer
H. Tennekes; A. G. M. Driedonks
The parameterization of penetrative convection and other cases of turbulent entrainment by the atmospheric boundary layer is reviewed in this paper. The conservation equations for a one-layer model of entrainment are straightforward; all modeling problems arise in the context of the parameterization of various terms in the budget of turbulent kinetic energy. There is no consensus in the literature on
Urban air pollution modelling and measurements of boundary layer height
F. Davies; D. R. Middleton; K. E. Bozier
An urban field trial has been undertaken with the aim of assessing the performance of the boundary layer height (BLH) determination of two models: the Met Office Unified Model (UM) and a Gaussian-type plume model, ADMS. Pulsed Doppler lidar data were used to measure mixing layer height and cloud base heights for a variety of meteorological conditions over a 3
The Boundary Layer between Electrodes and a Thermal Plasma
S. A. Self; L. D. Eskin
The electrical boundary layer between an isothermal, weakly ionized plasma and a plane electrode is discussed. Following a formulation of the complete problem, the governing equations are solved in the quasi-neutral continuum approximation to give explicit results for the ionization nonequilibrium layer. This allows three critical current densities to be identified: the first when a cathode must emit electrons; the
EART 265 Lecture Notes: Boundary Layers We're interested here mainly in boundary layers relevant to planets, i.e. those of planetary atmo-
Nimmo, Francis
EART 265 Lecture Notes: Boundary Layers We're interested here mainly in boundary layers relevant to planets, i.e. those of planetary atmo- spheres, oceans and uid cores. Of these, the atmospheric boundary. There is a another class of important boundary layer problems involving aerodynamics of objects moving in uids, i
An experimental investigation of turbulent boundary layers along curved surfaces
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.
Horton, pipe hydraulics, and the atmospheric boundary layer (The Robert E. Horton Memorial Lecture)
NASA Technical Reports Server (NTRS)
Brutsaert, Wilfried
The early stages of Horton's scientific career which provided the opportunity and stimulus to delve into the origins of some contemporary concepts on the atmospheric boundary layer are reviewed. The study of Saph and Schoder provided basis for the experimental verification and validation of similarity by Blasius, Staton and Pannel, and for the subsequent developments that led to the present understanding of the turbulent boundary layer. Particular attention is given to incorporation of similarity and scaling in the analysis of turbulent flow.
The Temporal Behavior of the Atmospheric Boundary Layer in Israel
Uri Dayan; Jacob Rodnizki
Upper-air measurements collected for three consecutive years (1987-89) from the Israel Meteorological Service permanent sounding site, in Beit-Dagan, Israel, enabled the temporal behavior of the atmospheric boundary layer over Israel to be characterized. Data analyzed consisted of the layer depth, the thermal gradient within the layer, and occurrence frequency of radiative and elevated inversions. To adequately represent the multiyear seasonal
Three-dimensional Large Eddy Simulation of wave bottom boundary layer
NASA Astrophysics Data System (ADS)
Zhou, Z.; Hsu, T.
Bottom boundary layer developed under surface waves has been widely studied in the past few decades because of the crucial role it plays in hydrodynamic dissipation and sediment transport. However, most of the previous numerical research simplified the wave field above the bottom boundary layer as fully-developed oscillatory flow. Many processes, such as boundary layer streaming, are neglected. With the aim of better understanding bottom boundary layer processes under real waves and to further investigate the interaction between the surface generated turbulence (e.g., breaking waves; wave-current interaction) and bottom boundary layer turbulence, a numerical study of three-dimensional Large Eddy Simulation (LES) is carried out. OpenFOAM, an open-source C++ toolbox which provides a solver of 3D Navier-Stokes equations and free-surface tracking, is utilized with a dynamic Smagorinsky closure. An idealized domain that contains a single wave is established with periodic boundary conditions in the streamwise and spanwise directions. The width of the channel is sufficiently large to contain the largest turbulent eddies. Firstly, laboratory data of bottom boundary layer under non-breaking waves is used to validate the numerical model and a good agreement is obtained. A more detailed investigation of the three-dimensional bottom boundary layer of non-breaking waves, e.g., the distribution of shear stress, turbulence structure and boundary layer streaming are investigated. Model results are compared with those in an oscillatory channel flow to contrast the effect of the inhomogeneous wave field. During the conference, we will also present preliminary results for wave-current interaction and wave breaking processes.
Boundary-layer control by electric fields A feasibility study
Mendes, R V
A problem of great concern in aviation and submarine propulsion is the control of the boundary layer and, in particular, the methods to extend the laminar region as a means to decrease noise and fuel consumption. In this paper we study the flow of air along an airfoil when a layer of ionized gas and a longitudinal electric field are created in the boundary layer region. By deriving scaling solutions and more accurate numerical solutions we discuss the possibility of achieving significant boundary layer control for realistic physical parameters. Practical design formulas and criteria are obtained. We also discuss the perspectives for active control of the laminar-to-turbulent transition fluctuations by electromagnetic field modulation.
The effects of forcing on a single stream shear layer and its parent boundary layer
NASA Technical Reports Server (NTRS)
Haw, Richard C.; Foss, John F.
Forcing and its effect on fluid flows has become an accepted tool in the study and control of flow systems. It has been used both as a diagnostic tool, to explore the development and interaction of coherent structures, and as a method of controlling the behavior of the flow. A number of forcing methods have been used in order to provide a perturbation to the flow; among these are the use of an oscillating trailing edge, acoustically driven slots, external acoustic forcing, and mechanical piston methods. The effect of a planar mechanical piston forcing on a single stream shear layer is presented; it can be noted that this is one of the lesser studied free shear layers. The single stream shear layer can be characterized by its primary flow velocity scale and the thickness of the separating boundary layer. The velocity scale is constant over the length of the flow field; theta (x) can be used as a width scale to characterize the unforced shear layer. In the case of the forced shear layer the velocity field is a function of phase time and definition of a width measure becomes somewhat problematic.
The structure of a three-dimensional turbulent boundary layer
NASA Technical Reports Server (NTRS)
Degani, A. T.; Smith, F. T.; Walker, J. D. A.
The three-dimensional turbulent boundary layer is shown to have a self-consistent two-layer asymptotic structure in the limit of large Reynolds number. In a streamline coordinate system, the streamwise velocity distribution is similar to that in two-dimensional flows, having a defect-function form in the outer layer which is adjusted to zero at the wall through an inner wall layer. An asymptotic expansion accurate to two orders is required for the cross-stream velocity which is shown to exhibit a logarithmic form in the overlap region. The inner wall-layer flow is collateral to leading order but the influence of the pressure gradient, at large but finite Reynolds numbers, is not negligible and can cause substantial skewing of the velocity profile near the wall. Conditions under which the boundary layer achieves self-similarity and the governing set of ordinary differential equations for the outer layer are derived. The calculated solution of these equations is matched asymptotically to an inner wall-layer solution and the composite profiles so formed describe the flow throughout the entire boundary layer. The effects of Reynolds number and cross-stream pressure gradient on the crossstream velocity profile are discussed and it is shown that the location of the maximum cross-stream velocity is within the overlap region.
Boundary-value problem for two-dimensional fluctuations in boundary layers
S. Tsuge; H. L. Rogler
The streamwise evolution of disturbances in a boundary layer is described as an asymptotic solution of the forced Orr-Sommerfeld equation. The velocity fluctuations and their derivations are specified along the y-axis. With these boundary conditions, the effects are included of vortical and irrotational free stream disturbances, fluctuations originating from leading edges, and discrete eigenmodes. A Fourier transform in time and
An Estimation of Turbulent Kinetic Energy and Energy Dissipation Rate Based on Atmospheric Boundary Layer Similarity Theory
NASA Technical Reports Server (NTRS)
Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)
Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.
Numerical Studies of Boundary-Layer Receptivity
NASA Technical Reports Server (NTRS)
Reed, Helen L.
Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.
Laminar boundary layers behind blast and detonation waves
NASA Astrophysics Data System (ADS)
Du, X.; Liu, W. S.; Glass, I. I.
Boundary layer flows in air behind nonuniform strong blast waves and in the burned gas of a stoichiometric mixture of hydrogen and oxygen behind uniform Chapman-Jouguet detonation waves were investigated. The results show that the Prandtl number profoundly influences boundary layer flow. For a blast wave and Pr less than unity it controls a boundary layer velocity overshoot which decreases with increasing Prandtl number. For a Chapman-Jouguet detonation wave similar results are obtained for a Pr = 0.72; however, for an actual Pr = 2.26, a flow reversal occurs away from the wave where the inviscid flow velocity approaches a small value. The viscous exponent was found to have a significant effect on the wall shear stresses and heat transfer. The effect of the wall temperature is small. Velocity profiles were computed for spherical and planar detonation waves. Because of the rapid decrease in density behind a blast wave, the boundary layer thickness becomes very much larger than their detonation wave counterparts at the same wave velocity (but different physical conditions). The velocity boundary layer thickness in air behind a quasistationary planar shock wave is somewhat more than for a planar detonation wave at the same wave velocity (but in different gases). The heat transfer to the wall behind a planar detonation wave was calculated.
Strong vortex/boundary layer interactions. I - Vortices high
NASA Astrophysics Data System (ADS)
Cutler, A. D.; Bradshaw, P.
Detailed measurements with hot-wires and pressure probes are presented for the interaction between a turbulent longitudinal vortex pair with 'common flow' down, and a turbulent boundary layer. The interaction has a larger value of the vortex circulation parameter, and therefore better represents many aircraft/vortex interactions, than those studied previously. The vortices move down towards the boundary layer, but only the outer parts of the vortices actually enter it. Beneath the vortices the boundary layer is thinned by lateral divergence to the extent that it almost ceases to grow. Outboard of the vortices the boundary layer is thickened by lateral convergence. The changes in turbulence structure parameters in the boundary layer appear to be due to the effects of 'extra-rate-of-strain' produced by lateral divergence (or convergence) and by free-stream turbulence. The effect of the interaction on the vortices (other than the inviscid effect of the image vortices below the surface) is small. The flow constitutes a searching test case for prediction methods for three-dimensional turbulent flows.
Stabilization of boundary layer streaks by plasma actuators
NASA Astrophysics Data System (ADS)
Riherd, Mark; Roy, Subrata
A flow's transition from laminar to turbulent leads to increased levels of skin friction. In recent years, dielectric barrier discharge actuators have been shown to be able to delay the onset of turbulence in boundary layers. While the laminar to turbulent transition process can be initiated by several different instability mechanisms, so far, only stabilization of the Tollmien-Schlichting path to transition has received significant attention, leaving the stabilization of other transition paths using these actuators less explored. To fill that void, a bi-global stability analysis is used here to examine the stabilization of boundary layer streaks in a laminar boundary layer. These streaks, which are important to both transient and by-pass instability mechanisms, are damped by the addition of a flow-wise oriented plasma body force to the boundary layer. Depending on the magnitude of the plasma actuation, this damping can be up to 25% of the perturbation's kinetic energy. The damping mechanism appears to be due to highly localized effects in the immediate vicinity of the body force, and when examined using a linearized Reynolds-averaged Navier-Stokes energy balance, indicate negative production of the perturbation's kinetic energy. Parametric studies of the stabilization have also been performed, varying the magnitude of the plasma actuator's body force and the spanwise wavenumber of the actuation. Based on these parametric studies, the damping of the boundary layer streaks appears to be linear with respect to the total amount of body force applied to the flow.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
A study of the attenuation of bending boundary layers in balanced and unbalanced, symmetrically and unsymmetrically laminated cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize the effects of laminate orthotropy and anisotropy on the bending boundary-layer decay length in a very general manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all laminates considered, the results show that the differences between results obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that, in some cases, neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and, in other cases, results in an overestimation.
Shuttle Return To Flight Experimental Results: Protuberance Effects on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Berry, Scott A.; Horvath, Thomas J.
The effect of isolated roughness elements on the windward boundary layer of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamic Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental effort was initiated to provide a roughness effects database for developing transition criteria to support on-orbit decisions to repair damage to the thermal protection system. Boundary layer transition results were obtained using trips of varying heights and locations along the centerline and attachment lines of 0.0075-scale models. Global heat transfer images using phosphor thermography of the Orbiter windward surface and the corresponding heating distributions were used to infer the state of the boundary layer (laminar, transitional, or turbulent). The database contained within this report will be used to formulate protuberance-induced transition correlations using predicted boundary layer edge parameters.
Effects of Riblets on Skin Friction in High-Speed Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Duan, Lian; Choudhari, Meelan M.
Direct numerical simulations of spatially developing turbulent boundary layers over riblets are conducted to examine the effects of riblets on skin friction at supersonic speeds. Zero-pressure gradient boundary layers with an adiabatic wall, a Mach number of M1 = 2.5, and a Reynolds number based on momentum thickness of Re = 1720 are considered. Simulations are conducted for boundary-layer flows over a clean surface and symmetric V- groove riblets with nominal spacings of 20 and 40 wall units. The DNS results confirm the few existing experimental observations and show that a drag reduction of approximately 7% is achieved for riblets with proper spacing. The influence of riblets on turbulence statistics is analyzed in detail with an emphasis on identifying the differences, if any, between the drag reduction mechanisms for incompressible and high-speed boundary layers.
Mass Transport through the Carrier Gas Boundary Layer in Organic Vapor Phase Deposition
NASA Astrophysics Data System (ADS)
Rolin, Cedric; Song, Byeongseop; Forrest, Stephen R.
We investigate the dynamics of molecular transport across the gas boundary layer formed above a cold substrate used in the organic vapor phase deposition of small organic molecules. The boundary layer properties ultimately determine film thickness uniformity and morphology, and material utilization efficiency. We use laser-induced fluorescence to spatially resolve the temperature and the concentration of organic molecules within the boundary layer. Under conditions typically used in organic vapor phase deposition of chamber pressures less than 5 torr, we find that the boundary layer extends to a remarkable distance of over 10 cm from the cooled substrate surface. Analytical and numerical models of molecular transport processes are developed to understand the transport of organic molecules to the substrate. Our models provide insights into conditions required to optimize film uniformity and material utilization efficiency in the growth of organic electronic devices.
A preliminary investigation of boundary-layer transition along a flat plate with adverse pressure gradient
NASA Technical Reports Server (NTRS)
Von Doenhoff, Albert E
Boundary-layer surveys were made throughout the transition region along a smooth flat plate placed in an airstream of practically zero turbulence and with an adverse pressure gradient. The boundary-layer Reynolds number at the laminar separation point was varied from 1,800 to 2,600. The test data, when considered in the light of certain theoretical deductions, indicated that transition probably began with separation of the laminar boundary layer. The extent of the transition region, defined as the distance from a calculated laminar separation point to the position of the first fully developed turbulent boundary-layer profile, could be expressed as a constant Reynolds number run of approximately 70,000. Some speculations are presented concerning the application of the foregoing concepts, after certain assumptions have been made, to the problem of the connection between transition on the upper surface of an airfoil at high angles of attack and the maximum lift.
Investigations of shock wave boundary layer interaction on suction side of compressor profile
NASA Astrophysics Data System (ADS)
Piotrowicz, M.; Flaszy?ski, P.; Doerffer, P.
The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to look more closely into the flow structure on the suction side of a blade, a design of a generic test section in linear transonic wind tunnel was proposed. The test section which could reproduce flow structure, shock wave location, pressure distribution and boundary layer development similar to the obtained on a cascade profile is the main objective of the presented here design. The design of the proposed test section is very challenging, because of shock wave existence, its interaction with boundary layer and its influence on the 3-D flow structure in the test section.
Non-linear processes in the Earth atmosphere boundary layer
NASA Astrophysics Data System (ADS)
Grunskaya, Lubov; Valery, Isakevich; Dmitry, Rubay
The work is connected with studying electromagnetic fields in the resonator Earth-Ionosphere. There is studied the interconnection of tide processes of geophysical and astrophysical origin with the Earth electromagnetic fields. On account of non-linear property of the resonator Earth-Ionosphere the tides (moon and astrophysical tides) in the electromagnetic Earth fields are kinds of polyharmonic nature. It is impossible to detect such non-linear processes with the help of the classical spectral analysis. Therefore to extract tide processes in the electromagnetic fields, the method of covariance matrix eigen vectors is used. Experimental investigations of electromagnetic fields in the atmosphere boundary layer are done at the distance spaced stations, situated on Vladimir State University test ground, at Main Geophysical Observatory (St. Petersburg), on Kamchatka pen., on Lake Baikal. In 2012 there was continued to operate the multichannel synchronic monitoring system of electrical and geomagnetic fields at the spaced apart stations: VSU physical experimental proving ground; the station of the Institute of Solar and Terrestrial Physics of Russian Academy of Science (RAS) at Lake Baikal; the station of the Institute of volcanology and seismology of RAS in Paratunka; the station in Obninsk on the base of the scientific and production society "Typhoon". Such investigations turned out to be possible after developing the method of scanning experimental signal of electromagnetic field into non- correlated components. There was used a method of the analysis of the eigen vectors ofthe time series covariance matrix for exposing influence of the moon tides on Ez. The method allows to distribute an experimental signal into non-correlated periodicities. The present method is effective just in the situation when energetical deposit because of possible influence of moon tides upon the electromagnetic fields is little. There have been developed and realized in program components in the form of PAS instruments of processes of geophysical and man-triggered nature; to predict the presence of the features of geophysical nature in the electromagnetic field of the atmosphere boundary surface layer; to study dynamics the analyzed signals coming from the geophysical and man-triggered sources in the electrical and magnetic fields of the atmosphere boundary surface layer; to expose changes of the investigated time series in the periods preceding the appearance of the predicted phenomena; to form clusters of the time series being the features of the predicted events. On the base of the exposed clusters of the time series there have been built the predicting rules allowing to coordinate the probability of appearing the groups of the occurred events. The work is carried out with supporting of Program FPP #14.B37.210668, FPP #5.2071.2011, RFBR #11-05-97518.
A revised conceptual model of the tropical marine boundary layer
NASA Astrophysics Data System (ADS)
Davison, Jennifer L.
This work consists of the development and validation of a new radar product based on Bragg scattering retrievals from clear air S-band radar returns, a re-conceptualization of the tropical marine boundary layer based on this new radar product, and supplemental analysis of other data from this environment. The running theme throughout is moisture variability---its presence, how it can be better detected, and how it should be portrayed in the tropical marine environment. Data examined include National Center for Atmospheric Research's (NCAR's) S-band Dual Polarization (S-Pol) radar data, rawinsondes, dropsondes, and portable automated mesonet surface station (PAMS) data from the Rain in Cumulus over the Ocean (RICO) field campaign, along with satellite data which was partially coincident with these other data sets. Dropsondes, released in 34 sets of �6 per set, with each sonde released 5 min (30 km) apart around a 60 km diameter circle, demonstrated both the high moisture variability in the tropical marine boundary layer (TMBL) and the inadequacy of an individual sounding for characterizing its moisture field. Same altitude relative humidity (RH) measurements varied by as much as 70% (7-8 g kg-1) and the TMBL top altitude could vary by 2+ km across a single set. Clear-air Bragg scattering layers (BSLs) were common during RICO. An algorithm was developed to determine the location of BSL base and top altitudes, which were used to generate time-height diagrams. These revealed long-lived coherent structure. A statistical comparison of BSL altitudes and RH profiles from the rawinsondes supported the hypothesis that BSL tops are found near altitudes associated with RH minima and BSL bases near altitudes of RH maxima. Mechanisms for BSL formation/maintenance were discussed. On average 4-5 BSLs were detected (including the transition layer), and each BSL as well as the "clear" layers separating them had median depths of 350 m. Both BSLs and clear layers tended to be deeper on days with higher rain rates, and more (fewer) layers tended to be present when surface winds were more southerly (northerly). BSL statistics serve as the basis for a revised conceptual model of the TMBL, which contains 2-3 more layers of enhanced static stability, layered structure to the moisture variability and extends more than a km higher than the previous conceptual model. When compared, the distribution curves as functions of altitude for 1) BSL tops and 2) satellite derived cloud top heights had a correlation coefficient of 0.92, lending satellite support to the radar portrayal of the TMBL. Frequency by altitude diagrams (FADs) of rawinsonde data showed that the TMBL was sufficiently turbulent to support the Bragg scattering. RH gradients across 350 m intervals ranged from changes of greater than 95% to less than -60%, and all values of RH had a nearly equal probability of occurrence between 2 and 4 km. There were no preferred heights for temperature inversions, with inversions found across both 50 m and 350 m intervals for all altitudes above 1.2 km. The FAD of equivalent potential temperature indicated that the air modified by the ocean typically extended up to 4 km. Disturbed days (e.g., those with rain rates > 2 mm day-1) tended to be moister---with the moisture extending higher, than undisturbed days. The disturbed days also tended to be cooler between 2 and 4.5 km and have less northerly winds in the lowest 4 km.
Interferometric data for a shock-wave/boundary-layer interaction
NASA Technical Reports Server (NTRS)
Dunagan, Stephen E.; Brown, James L.; Miles, John B.
An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.
Effect of curvature on three-dimensional boundary layer stability
NASA Technical Reports Server (NTRS)
Malik, M. R.; Poll, D. I. A.
The problem of the stability of a three-dimensional laminar boundary layer formed on a curved surface is considered. A calculation scheme, which takes account of the curvature of the flow streamlines and of the surface is proposed for the prediction of the development of small amplitude temporal disturbances. Computations have been performed for the flow over the windward face of an infinitely long yawed cylinder and comparisons have been made with experimental data. These indicate that the theory correctly predicts many of the features of the unstable laminar flow. The theory also suggests that transition, in this particular situation, is dominated by traveling disturbance waves and that, at the experimentally observed transition location, the wave which has undergone greatest total amplification has an amplitude ratio of approximately e to the 11th. When the effects of curvature are omitted the maximum amplitude ratio at transition is about e to the 17th.
Instabilities in the boundary layer over a permeable, compliant wall
NASA Astrophysics Data System (ADS)
Pluvinage, Franck; Kourta, Azeddine; Bottaro, Alessandro
Local linear stability of swept and unswept incompressible boundary layers developing over compliant, fluid-saturated, porous plates is considered in the limit of small permeability. The analysis is meant to yield preliminary indications on the possible stabilization induced on the flow's hydrodynamic and hydroelastic modes by poroelastic media, such as those occurring in many natural and technological settings. As far as hydrodynamic modes are concerned, the main stabilizing effect is that of compliance, which however couples weakly to low-frequency crossflow modes. Permeability plays a damping role on hydroelastic modes, which here take the form of travelling wave flutter instabilities. The passive control of instabilities through poroelastic coatings specifically designed to selectively exploit the effect of compliance and/or permeability is a subject worthy of future research efforts.
Combined core/boundary layer transport simulations in tokamaks
Prinja, A.K.; Schafer, R.F. Jr.; Conn, R.W.; Howe, H.C.
Significant new numerical results are presented from self-consistent core and boundary or scrape-off layer plasma simulations with 3-D neutral transport calculations. For a symmetric belt limiter it is shown that, for plasma conditions considered here, the pump limiter collection efficiency increases from 11% to 18% of the core efflux as a result of local reionization of blade deflected neutrals. This hitherto unobserved effect causes a significant amplification of upstream ion flux entering the pump limiter. Results from coupling of an earlier developed two-zone edge plasma model ODESSA to the PROCTR core plasma simulation code indicates that intense recycling divertor operation may not be possible because of stagnation of upstream flow velocity. This results in a self-consistent reduction of density gradient in an intermediate region between the central plasma and separatrix, and a concomitant reduction of core-efflux. There is also evidence of increased recycling at the first wall.
The numerical calculation of laminar boundary-layer separation
NASA Technical Reports Server (NTRS)
Klineberg, J. M.; Steger, J. L.
Iterative finite-difference techniques are developed for integrating the boundary-layer equations, without approximation, through a region of reversed flow. The numerical procedures are used to calculate incompressible laminar separated flows and to investigate the conditions for regular behavior at the point of separation. Regular flows are shown to be characterized by an integrable saddle-type singularity that makes it difficult to obtain numerical solutions which pass continuously into the separated region. The singularity is removed and continuous solutions ensured by specifying the wall shear distribution and computing the pressure gradient as part of the solution. Calculated results are presented for several separated flows and the accuracy of the method is verified. A computer program listing and complete solution case are included.
Boundary-layer-ingesting inlet flow control system
NASA Technical Reports Server (NTRS)
Owens, Lewis R. (Inventor); Allan, Brian G. (Inventor)
A system for reducing distortion at the aerodynamic interface plane of a boundary-layer-ingesting inlet using a combination of active and passive flow control devices is disclosed. Active flow control jets and vortex generating vanes are used in combination to reduce distortion across a range of inlet operating conditions. Together, the vortex generating vanes can reduce most of the inlet distortion and the active flow control jets can be used at a significantly reduced control jet mass flow rate to make sure the inlet distortion stays low as the inlet mass flow rate varies. Overall inlet distortion, measured and described as average SAE circumferential distortion descriptor, was maintained at a value of 0.02 or less. Advantageous arrangements and orientations of the active flow control jets and the vortex generating vanes were developed using computational fluid dynamics simulations and wind tunnel experimentations.
Behavior of the Laminar Boundary Layer for Periodically Oscillating Pressure Variation
NASA Technical Reports Server (NTRS)
Quick, august Wilhelm; Schroeder, K.
The calculation of the phenomena within the boundary layer of bodies immersed in a flow underwent a decisive development on the basis of L. Prandtl's trains of thought, stated more than forth years ago, and by numerous later treatises again and again touching upon them. The requirements of the steadily improving aerodynamics of airplanes have greatly increased with the passing of time and recently research became particularly interested in such phenomena in the boundary layer as are caused by small external disturbances. Experimental results suggest that, for instance, slight fluctuations in the free stream velocities as they occur in wind tunnels or slight wavelike deviations of outer wing contours from the prescribed smooth course as they originate due to construction inaccuracies may exert strong effects on the extent of the laminar boundary layer on the body and thus on the drag. The development of turbulence in the last part of the laminar portion of the boundary layer is, therefore, the main problem, the solution of which explains the behavior of the transition point of the boundary layer. A number of reports in literature deal with this problem,for instance, those of Tollmien, Schlichting, Dryden, and Pretsch. The following discussion of the behavior of the laminar boundary layer for periodically oscillating pressure variation also purports to make a contribution to that subject.
Turbulence intensity similarity laws for high Reynolds number boundary layers
NASA Astrophysics Data System (ADS)
Kunkel, Gary; Marusic, Ivan
Data obtained in the surface layer of the atmospheric boundary layer at the SLTEST (Surface Layer Turbulence and Environmental Science Test) facility located on the western Utah salt flats are used to analyze current turbulence intensity similarity laws. The high Reynolds number data are shown to be consistent with the Marusic, Uddin and Perry (Phys. Fluids 1997) formulation which applies for the outer region of the boundary layer, approximately 100 <= z+ <= Re_?. Here z is wall-normal position and Re_? is the Reynolds number based on boundary layer thickness and friction velocity. This formulation is based on the attached eddy hypothesis and shows that the streamwise turbulence intensity normalized with friction velocity scales as a function of both z+ and Re_?, while the wall-normal turbulence intensity scales only with wall variables. Corresponding spectra will also be presented. Additional laboratory experimental data will be analyzed and a new extended formulation will be presented which applies across the entire boundary layer. The extended formulation appears to explain the empirical mixed inner and outer velocity scaling proposed by DeGraaff and Eaton ( J. Fluid Mech. 2000).
Vortex Generators to Control Boundary Layer Interactions
NASA Technical Reports Server (NTRS)
Babinsky, Holger (Inventor); Loth, Eric (Inventor); Lee, Sang (Inventor)
Devices for generating streamwise vorticity in a boundary includes various forms of vortex generators. One form of a split-ramp vortex generator includes a first ramp element and a second ramp element with front ends and back ends, ramp surfaces extending between the front ends and the back ends, and vertical surfaces extending between the front ends and the back ends adjacent the ramp surfaces. A flow channel is between the first ramp element and the second ramp element. The back ends of the ramp elements have a height greater than a height of the front ends, and the front ends of the ramp elements have a width greater than a width of the back ends.
Turbulence models for compressible boundary layers
NASA Technical Reports Server (NTRS)
Huang, P. G.; Bradshaw, P.; Coakley, T. J.
It is shown that to satisfy the general accepted compressible law of the wall derived from the Van Driest transformation, turbulence modeling coefficients must actually be functions of density gradients. The transformed velocity profiles obtained by using standard turbulence model constants have too small a value of the effective von Karman constant kappa in the log-law region (inner layer). Thus, if the model is otherwise accurate, the wake component is overpredicted and the predicted skin friction is lower than the expected value.
Influence of the thermal boundary layer on the contact layer between a liquid and a cold plate in a solidification process
NASA Astrophysics Data System (ADS)
Lipnicki, Z.; Weigand, B.
In this paper, the influence of both the hydrodynamic and the thermal boundary layer on the solidification process of the flowing liquid on a cold plate is theoretically analyzed. Heat transfer between a frozen layer which is created and a laminar flowing liquid over that layer is considered. The development of the boundary layers and the relation between them on the solidification process are studied. An integral method for the solution of the boundary layer equations was used to obtain approximative solutions. The influence of the Prandtl and Reynolds number on the formation of the solid crust is shown and discussed for time dependent and steady-state solutions.
Roughness Induced Transition in a Supersonic Boundary Layer
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam; Kergerise, Michael A.
Direct numerical simulation is used to investigate the transition induced by threedimensional isolated roughness elements in a supersonic boundary layer at a free stream Mach number of 3.5. Simulations are performed for two different configurations: one is a square planform roughness and the other is a diamond planform roughness. The mean-flow calculations show that the roughness induces counter rotating streamwise vortices downstream of the roughness. These vortices persist for a long distance downstream and lift the low momentum fluid from the near wall region and place it near the outer part of the boundary layer. This forms highly inflectional boundary layer profiles. These observations agree with recent experimental observations. The receptivity calculations showed that the amplitudes of the mass-flux fluctuations near the neutral point for the diamond shape roughness are the same as the amplitude of the acoustic disturbances. They are three times smaller for the square shape roughness.
The Turbulent Boundary Layer on a Rough Curvilinear Surface
NASA Technical Reports Server (NTRS)
Droblenkov, V. F.
A number of semiempirical approximate methods exist for determining the characteristics of the turbulent boundary layer on a curvilinear surface. At present, among these methods, the one proposed by L. G. Loitsianskii is given frequent practical application. This method is sufficiently effective and permits, in the case of wing profiles with technically smooth surfaces, calculating the basic characteristics of the boundary layer and the values of the overall drag with an accuracy which suffices for practical purposes. The idea of making use of the basic integral momentum equation ((d delta(sup xx))/dx) + ((V' delta(sup xx))/V) (2 + H) = (tau(sub 0))/(rho V(exp 2)) proves to be fruitful also for the solution of the problems in the determination of the characteristics of the turbulent boundary layer on a rough surface.
Sound from boundary layer flow over steps and gaps
NASA Astrophysics Data System (ADS)
Ryan Catlett, M.; Devenport, William; Glegg, Stewart A. L.
This study is concerned with the radiated sound from boundary layer flows over small forward and backward steps and gap configurations of similar dimension. These measurements were performed in the Virginia Tech Anechoic Wall Jet Facility for step heights that ranged from approximately 10 percent to 100 percent of the incoming boundary layer height. The results show the influence of step height and boundary layer edge velocity on the far-field sound from forward and backward steps. Neither source shows clear dipole directivity and at least the larger step heights considered in this study are shown to not be acoustically compact. A new mixed scaling normalization is proposed for the far-field spectra from both types of step. Backward steps are shown to be much weaker producers of far-field sound than similarly sized forward steps. The implications of this behavior are discussed with respect to the far-field sound measured from various gap flows.
Effect of Blowing on Boundary Layer of Scarf Inlet
NASA Technical Reports Server (NTRS)
Gerhold, Carl H.; Clark, Lorenzo R.
When aircraft operate in stationary or low speed conditions, airflow into the engine accelerates around the inlet lip and pockets of turbulence that cause noise and vibration can be ingested. This problem has been encountered with engines equipped with the scarf inlet, both in full scale and in model tests, where the noise produced during the static test makes it difficult to assess the noise reduction performance of the scarf inlet. NASA Langley researchers have implemented boundary layer control in an attempt to reduce the influence of the flow nonuniformity in a 12-in. diameter model of a high bypass fan engine mounted in an anechoic chamber. Static pressures and boundary layer profiles were measured in the inlet and far field acoustic measurements were made to assess the effectiveness of the blowing treatment. The blowing system was found to lack the authority to overcome the inlet distortions. Methods to improve the implementation of boundary layer control to reduce inlet distortion are discussed.
A compilation of unsteady turbulent boundary-layer experimental data
NASA Technical Reports Server (NTRS)
Carr, L. W.
An extensive literature search was conducted and those experiments related to unsteady boundary layer behavior were cataloged. In addition, an international survey of industrial, university, and governmental research laboratories was made in which new and ongoing experimental programs associated with unsteady turbulent boundary layer research were identified. Pertinent references were reviewed and classified based on the technical emphasis of the various experiments. Experiments that include instantaneous or ensemble averaged profiles of boundary layer variables are stressed. The experimental apparatus and flow conditions are described and summaries of acquired data and significant conclusions are summarized. Measurements obtained from the experiments which exist in digital form were stored on magnetic tape. Instructions are given for accessing these data sets for further analysis.
Modeling large wind farms in conventionally neutral atmospheric boundary layers under varying initial conditions
NASA Astrophysics Data System (ADS)
Allaerts, Dries; Meyers, Johan
Atmospheric boundary layers (ABL) are frequently capped by an inversion layer limiting the entrainment rate and boundary layer growth. Commonly used analytical models state that the entrainment rate is inversely proportional to the inversion strength. The height of the inversion turns out to be a second important parameter. Conventionally neutral atmospheric boundary layers (CNBL) are ABLs with zero surface heat flux developing against a stratified free atmosphere. In this regime the inversion-filling process is merely driven by the downward heat flux at the inversion base. As a result, CNBLs are strongly dependent on the heating history of the boundary layer and strong inversions will fail to erode during the course of the day. In case of large wind farms, the power output of the farm inside a CNBL will depend on the height and strength of the inversion above the boundary layer. On the other hand, increased turbulence levels induced by wind farms may partially undermine the rigid lid effect of the capping inversion, enhance vertical entrainment of air into the farm, and increase boundary layer growth. A suite of large eddy simulations (LES) is performed to investigate the effect of the capping inversion on the conventionally neutral atmospheric boundary layer and on the wind farm performance under varying initial conditions. For these simulations our in-house pseudo-spectral LES code SP-Wind is used. The wind turbines are modelled using a non-rotating actuator disk method. In the absence of wind farms, we find that a decrease in inversion strength corresponds to a decrease in the geostrophic angle and an increase in entrainment rate and geostrophic drag. Placing the initial inversion base at higher altitudes further reduces the effect of the capping inversion on the boundary layer. The inversion can be fully neglected once it is situated above the equilibrium height that a truly neutral boundary layer would attain under the same external conditions such as geostrophic wind speed and surface roughness. Wind farm simulations show the expected increase in boundary layer height and growth rate with respect to the case without wind farms. Raising the initial strength of the capping inversion in these simulations dampens the turbulent growth of the boundary layer above the farm, decreasing the farms energy extraction. The authors acknowledge support from the European Research Council (FP7-Ideas, grant no. 306471). Simulations were performed on the computing infrastructure of the VSC Flemish Supercomputer Center, funded by the Hercules Foundation and the Flemish Government.
The turbulent boundary layer directly behind the reattachment of a separation area
P. Wauschkuhn; V. Vasanta Ram
The parameters measured in the study include the pressure distribution at the wall, the wall shear stress characteristics, the distribution of the mean velocity in the boundary layer, and the distribution of the Reynolds shear stress in the boundary layer. The relaxation characteristics of the boundary layer are discussed. The characteristics of the flow in the boundary layer do not
Spectral characteristics of velocity and vorticity fluxes in an unstratified turbulent boundary layer
Lien, Ren-Chieh
with the empirical form found in the atmospheric boundary layer. In the inertial subrange the momentum flux of turbulence spectral properties have been conducted in the atmospheric boundary layer, e.g., the 1968 Kansas spectral properties in the oceanic boundary layer com- pared to studies in the atmospheric boundary layer
Surface heterogeneity effects on regional-scale fluxes in stable boundary layers: surface temperature transitions
Stoll, Rob
understanding of homogeneous stable boundary layers (SBLs). However, in general, the atmospheric boundary layerSurface heterogeneity effects on regional-scale fluxes in stable boundary layers: surface temperature distributions on regional-scale turbulent fluxes in the stable boundary layer (SBL). Simulations
Time Scales of the Trade Wind Boundary Layer Adjustment GILLES BELLON
Ribes, Aur�lien
of the trade wind atmospheric boundary layer to an abrupt sea surface warming is in- vestigated using a large of the boundary layer depth. 1. Introduction The trade wind atmospheric boundary layer can be consideredTime Scales of the Trade Wind Boundary Layer Adjustment GILLES BELLON Centre National de Recherches
De Bilt, 2010 | Technical report; TR-315 Assimilation of Cabauw boundary layer
Stoffelen, Ad
;#12;Assimilation of Cabauw boundary layer observations in an atmospheric single-column model using an ensemble the structure and transport properties of the atmospheric boundary layer (ABL). Boundary layer processes have the full atmospheric column over the Netherland of which the atmospheric boundary layer forms the lowest
Entrainment results from the Flatland boundary layer experiments
NASA Astrophysics Data System (ADS)
Angevine, Wayne M.; Grimsdell, Alison W.; McKeen, Stuart A.; Warnock, J. M.
A primary objective of the 1995 and 1996 Flatland boundary layer experiments, known as Flatland95 and Flatland96, was to measure and characterize entrainment at the top of the convective boundary layer. The experiments took place in the area near the Flatland Atmospheric Observatory near Champaign-Urbana, Illinois, in August-September 1995 and June-August 1996. The site is interesting because it is extraordinarily flat, has uniform land use, and is situated in a prime agricultural area. Measurements in the entrainment zone are difficult to make due to the time and space scales involved. We will present entrainment estimates derived from budget calculations with data from UHF wind profiling radars and from radiosondes. The results demonstrate that the remote sensing instruments produce results comparable to radiosondes and have significant advantages for boundary layer studies. Surface flux measurements are also used in the calculations. Direct heating by shortwave radiation absorbed by aerosols in the boundary layer is found to be an important component of the boundary layer heat budgets. The entrainment virtual temperature flux and the ratio of entrainment to surface flux found from the budget calculations are somewhat larger than expected. Advection of warm air, which is not accounted for in the budget calculations, is probably a factor in some periods but may not be significant in the full data set. For the full data set, the mean entrainment velocity found from the heat budget is 0.03�0.01 m s-1, slightly less than the mean rate of change of the boundary layer height. The mean entrainment ratio AR is 0.51�0.12 and the median is 0.43, comparable to results from some other studies in comparable conditions.
Receptivity of Hypersonic Boundary Layers over Straight and Flared Cones
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam; Kegerise, Michael A.
The effects of adverse pressure gradients on the receptivity and stability of hypersonic boundary layers were numerically investigated. Simulations were performed for boundary layer flows over a straight cone and two flared cones. The steady and the unsteady flow fields were obtained by solving the two-dimensional Navier-Stokes equations in axi-symmetric coordinates using the 5th order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The mean boundary layer profiles were analyzed using local stability and non-local parabolized stability equations (PSE) methods. After the most amplified disturbances were identified, two-dimensional plane acoustic waves were introduced at the outer boundary of the computational domain and time accurate simulations were performed. The adverse pressure gradient was found to affect the boundary layer stability in two important ways. Firstly, the frequency of the most amplified second-mode disturbance was increased relative to the zero pressure gradient case. Secondly, the amplification of first- and second-mode disturbances was increased. Although an adverse pressure gradient enhances instability wave growth rates, small nose-tip bluntness was found to delay transition due to the low receptivity coefficient and the resulting weak initial amplitude of the instability waves. The computed and measured amplitude-frequency spectrums in all three cases agree very well in terms of frequency and the shape except for the amplitude.
Interaction between strong longitudinal vortices and turbulent boundary layers
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Naaseri, M.; Bradshaw, P.
The latest stages of work on the interaction between longitudinal vortices and turbulent boundary layers show that very large changes in turbulence structure occur when the vortices are strong (crossflow angles of order 20 deg). The changes are poorly correlated by current turbulence models and go well beyond the rotation of the stress tensor in the vortex region that is explicitly represented by the exact 'generation' (exchange) terms in the Reynolds-stress transport equations. Measurements in the interaction between a burst vortex and a boundary layer show qualitatively similar results to the unburst case, but shed useful light on the bursting process itself.
Characteristics of turbulence in boundary layer with zero pressure gradient
NASA Technical Reports Server (NTRS)
Klebanoff, P S
The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation (fluctuation in x-direction), spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.
Turbulent boundary layers subjected to multiple curvatures and pressure gradients
NASA Technical Reports Server (NTRS)
Bandyopadhyay, Promode R.; Ahmed, Anwar
The effects of abruptly applied cycles of curvatures and pressure gradients on turbulent boundary layers are examined experimentally. Two two-dimensional curved test surfaces are considered: one has a sequence of concave and convex longitudinal surface curvatures and the other has a sequence of convex and concave curvatures. The choice of the curvature sequences were motivated by a desire to study the asymmetric response of turbulent boundary layers to convex and concave curvatures. The relaxation of a boundary layer from the effects of these two opposite sequences has been compared. The effect of the accompaying sequences of pressure gradient has also been examined but the effect of curvature dominates. The growth of internal layers at the curvature junctions have been studied. Measurements of the Gortler and corner vortex systems have been made. The boundary layer recovering from the sequence of concave to convex curvature has a sustained lower skin friction level than in that recovering from the sequence of convex to concave curvature. The amplification and suppression of turbulence due to the curvature sequences have also been studied.
A model of the wall boundary layer for ducted propellers
NASA Astrophysics Data System (ADS)
Eversman, Walter; Moehring, Willi
The objective of the present study is to include a representation of a wall boundary layer in an existing finite element model of the propeller in the wind tunnel environment. The major consideration is that the new formulation should introduce only modest alterations in the numerical model and should still be capable of producing economical predictions of the radiated acoustic field. This is accomplished by using a stepped approximation in which the velocity profile is piecewise constant in layers. In the limit of infinitesimally thin layers, the velocity profile of the stepped approximation coincides with that of the continuous profile. The approach described here could also be useful in modeling the boundary layer in other duct applications, particularly in the computation of the radiated acoustic field for sources contained in a duct.
A model of the wall boundary layer for ducted propellers
NASA Technical Reports Server (NTRS)
Eversman, Walter; Moehring, Willi
The objective of the present study is to include a representation of a wall boundary layer in an existing finite element model of the propeller in the wind tunnel environment. The major consideration is that the new formulation should introduce only modest alterations in the numerical model and should still be capable of producing economical predictions of the radiated acoustic field. This is accomplished by using a stepped approximation in which the velocity profile is piecewise constant in layers. In the limit of infinitesimally thin layers, the velocity profile of the stepped approximation coincides with that of the continuous profile. The approach described here could also be useful in modeling the boundary layer in other duct applications, particularly in the computation of the radiated acoustic field for sources contained in a duct.
Hypersonic three-dimensional nonequilibrium boundary-layer equations in generalized curvilinear coordinates
NASA Technical Reports Server (NTRS)
Lee, Jong-Hun
The basic governing equations for the second-order three-dimensional hypersonic thermal and chemical nonequilibrium boundary layer are derived by means of an order-of-magnitude analysis. A two-temperature concept is implemented into the system of boundary-layer equations by simplifying the rather complicated general three-temperature thermal gas model. The equations are written in a surface-oriented non-orthogonal curvilinear coordinate system, where two curvilinear coordinates are non-orthogonial and a third coordinate is normal to the surface. The equations are described with minimum use of tensor expressions arising from the coordinate transformation, to avoid unnecessary confusion for readers. The set of equations obtained will be suitable for the development of a three-dimensional nonequilibrium boundary-layer code. Such a code could be used to determine economically the aerodynamic/aerothermodynamic loads to the surfaces of hypersonic vehicles with general configurations. In addition, the basic equations for three-dimensional stagnation flow, of which solution is required as an initial value for space-marching integration of the boundary-layer equations, are given along with the boundary conditions, the boundary-layer parameters, and the inner-outer layer matching procedure. Expressions for the chemical reaction rates and the thermodynamic and transport properties in the thermal nonequilibrium environment are explicitly given.
Two boundary layers in Titan's lower troposphere inferred from a climate model
NASA Astrophysics Data System (ADS)
Charnay, Benjamin; Lebonnois, S�bastien
Saturn's moon Titan has a dense atmosphere, but its thermal structure is poorly known. Conflicting information has been gathered on the nature, extent and evolution of Titan's planetary boundary layer--the layer of the atmosphere that is influenced by the surface--from radio-occultation observations by the Voyager 1 spacecraft and the Cassini orbiter, measurements by the Huygens probe and by dune-spacing analyses. Specifically, initial analyses of the Huygens data suggested a boundary layer of 300m depth with no diurnal evolution, incompatible with alternative estimates of 2-3km (refs , , ). Here we use a three-dimensional general circulation model, albeit not explicitly simulating the methane cycle, to analyse the dynamics leading to the thermal profile of Titan's lowermost atmosphere. In our simulations, a convective boundary layer develops in the course of the day, rising to an altitude of 800m. In addition, a seasonal boundary of 2km depth is produced by the reversal of the Hadley cell at the equinox, with a dramatic impact on atmospheric circulation. We interpret fog that had been discovered at Titan's south pole earlier as boundary layer clouds. We conclude that Titan's troposphere is well structured, featuring two boundary layers that control wind patterns, dune spacing and cloud formation at low altitudes.
Measurements of Unsteady Turbulent Boundary Layer Separation under Conditions Relevant to Helicopter Rotors
NASA Astrophysics Data System (ADS)
Schatzman, David; Thomas, Flint
A unique experimental facility was developed to study unsteady turbulent boundary layer separation under conditions relevant to helicopter rotors. The facility provides the capability for unsteady turbulent boundary layer separation measurements of high spatial and temporal resolution. Leading edge plasma flow control on a stalled airfoil is used as a tool to impose an unsteady pressure gradient on turbulent boundary layer flow over a convex ramp section. Plasma flow control is used to alternately attach and separate the airfoil flow which gives rise to unsteady turbulent boundary layer separation on the convex ramp. Phase locked PIV measurements are utilized to capture the dynamics of the unsteady turbulent boundary layer separation. High speed digital imaging of smoke flow visualization and simultaneous unsteady wall pressure records are used to track events that occur in the outer part of the boundary layer and propagate toward the wall. Joint hot-wire and unsteady wall pressure measurements are used to quantify these events during the unsteady separation process.
The Saharan atmospheric boundary layer: Turbulence, stratification and mixing
NASA Astrophysics Data System (ADS)
Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.
High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (?1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer concentrations, demonstrating the potential for variability in, for example, dust concentrations independent of external forcings. The residual layer, where long-range transport can take place, is analyzed in particular detail. Various processes which can lead to transport into and mixing within the residual layer are explored, including shear-driven turbulence at the residual layer top and the potential for detrainment from the convective boundary layer top due to the combination of a weak lid and a neutral layer above.
Nanoscale Hot-Wire Probes for Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Tedjojuwono, Ken T.; Herring, Gregory C.
Hot-wire probes having dimensions of the order of nanometers have been proposed for measuring temperatures (and possibly velocities) in boundary-layer flows at spatial resolutions much finer and distances from walls much smaller than have been possible heretofore. The achievable resolutions and minimum distances are expected to be of the order of tens of nanometers much less than a typical mean free path of a molecule and much less than the thickness of a typical flow boundary layer in air at standard temperature and pressure. An additional benefit of the small scale of these probes is that they would perturb the measured flows less than do larger probes. The hot-wire components of the probes would likely be made from semiconducting carbon nanotubes or ropes of such nanotubes. According to one design concept, a probe would comprise a single nanotube or rope of nanotubes laid out on the surface of an insulating substrate between two metallic wires. According to another design concept, a nanotube or rope of nanotubes would be electrically connected and held a short distance away from the substrate surface by stringing it between two metal electrodes. According to a third concept, a semiconducting nanotube or rope of nanotubes would be strung between the tips of two protruding electrodes made of fully conducting nanotubes or ropes of nanotubes. The figure depicts an array of such probes that could be used to gather data at several distances from a wall. It will be necessary to develop techniques for fabricating the probes. It will also be necessary to determine whether the probes will be strong enough to withstand the aerodynamic forces and impacts of micron-sized particles entrained in typical flows of interest.
Numerical Computations of Hypersonic Boundary-Layer over Surface Irregularities
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei
Surface irregularities such as protuberances inside a hypersonic boundary layer may lead to premature transition on the vehicle surface. Early transition in turn causes large localized surface heating that could damage the thermal protection system. Experimental measurements as well as numerical computations aimed at building a knowledge base for transition Reynolds numbers with respect to different protuberance sizes and locations have been actively pursued in recent years. This paper computationally investigates the unsteady wake development behind large isolated cylindrical roughness elements and the scaled wind-tunnel model of the trip used in a recent flight measurement during the reentry of space shuttle Discovery. An unstructured mesh, compressible flow solver based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for the flow past a roughness element under several wind-tunnel conditions. For a cylindrical roughness element with a height to the boundary-layer thickness ratio from 0.8 to 2.5, the wake flow is characterized by a mushroom-shaped centerline streak and horse-shoe vortices. While time-accurate solutions converged to a steady-state for a ratio of 0.8, strong flow unsteadiness is present for a ratio of 1.3 and 2.5. Instability waves marked by distinct disturbance frequencies were found in the latter two cases. Both the centerline streak and the horse-shoe vortices become unstable downstream. The oscillatory vortices eventually reach an early breakdown stage for the largest roughness element. Spectral analyses in conjunction with the computed root mean square variations suggest that the source of the unsteadiness and instability waves in the wake region may be traced back to possible absolute instability in the front-side separation region.
Bidirectional mixing in an ACE 1 marine boundary layer overlain by a second turbulent layer
NASA Astrophysics Data System (ADS)
Russell, Lynn M.; Lenschow, Donald H.; Laursen, Krista K.; Krummel, Paul B.; Siems, Steven T.; Bandy, Alan R.; Thornton, Donald C.; Bates, Timothy S.
In the Lagrangian B flights of the First Aerosol Characterization Experiment (ACE 1), the chemistry and dynamics of the postfrontal air mass were characterized by tracking a constant-level balloon launched into the air mass for three consecutive 8-hour flights of the instrumented National Center for Atmospheric Research C-130 aircraft during a 33-hour period. The boundary layer extended to a height of 400 to 700 m during this period, with its top defined by changes in the amount of turbulent mixing measured rather than by an inversion. Above the planetary boundary layer to a height of 1400 to 1900 m, a second layer was capped with a more pronounced temperature inversion and contained only intermittent turbulence. Since this layer served as a reservoir and mixing zone for boundary layer and free tropospheric air, we have called it a buffer layer to emphasize its differences from previous concepts of a residual or intermediate layer. Estimates of the entrainment rate of dimethyl sulfide (DMS) and aerosol particles between the boundary layer and the buffer layer demonstrated that exchange occurred across the interface between these two layers in both upward and downward directions. In situ measurements of aerosol particles revealed highly concentrated, nucleation-mode aerosol particles between 10 and 30 nm diameter at the beginning of the first Lagrangian B flight in the buffer layer, while few were present in the boundary layer. Observations during the second and third flights indicate that aerosol particles of this size were mixing downward into the boundary layer from the buffer layer while DMS was transported upward. This fortuitous enhancement of aerosol particles in the buffer layer allowed simultaneous use of DMS and aerosol particle budgets to track the bidirectional entrainment rates. These estimates were compared to those from measurements of mean vertical motion and boundary layer growth rate, and from estimates of the fluxes and changes in concentration across the layer interface. In addition, three different techniques were used to estimate DMS emission rates from the ocean surface and showed good agreement: (1) evalulation of the DMS and aerosol mean concentration budgets, (2) seawater DMS concentrations and an air-sea exchange velocity, and (3) the mixed-layer gradient technique.
Magnetic field maxima in the low latitude boundary layer
NASA Technical Reports Server (NTRS)
Sonnerup, B.; Paschmann, G.; Phan, T.-D.; Luehr, H.
The magnetic field often exhibits a maximum in the earth's low-latitude boundary layer. Examples of this behavior are shown using data from the AMPTE/IRM spacecraft, and it is argued that two fundamentally distinct causes exist for the excess field: (1) a depression, within the layer, of the population of medium-energy ions of magnetospheric origin and (2) field curvature effects associated with undulations of the magnetopause itself.
Some Turbulence Characteristics in Stable Atmospheric Boundary Layer Flow
Ann-Sofi Smedman
Atmospheric boundary layer measurements during stable and near neutral condition from seven sites in different kinds of terrain have been analyzed in order to find relationships among turbulence parameters.The shape of the spectral and cospectral distributions turned out to be well represented by the universal expressions found for ideal sites.For near neutral conditions in the surface layer w\\/u( increases and
Dynamic Turbulence Modelling in Large-eddy Simulations of the Cloud-topped Atmospheric Boundary Layer
NASA Technical Reports Server (NTRS)
Kirkpatrick, M. P.; Mansour, N. N.; Ackerman, A. S.; Stevens, D. E.
The use of large eddy simulation, or LES, to study the atmospheric boundary layer dates back to the early 1970s when Deardor (1972) used a three-dimensional simulation to determine velocity and temperature scales in the convective boundary layer. In 1974 he applied LES to the problem of mixing layer entrainment (Deardor 1974) and in 1980 to the cloud-topped boundary layer (Deardor 1980b). Since that time the LES approach has been applied to atmospheric boundary layer problems by numerous authors. While LES has been shown to be relatively robust for simple cases such as a clear, convective boundary layer (Mason 1989), simulation of the cloud-topped boundary layer has proved more of a challenge. The combination of small length scales and anisotropic turbulence coupled with cloud microphysics and radiation effects places a heavy burden on the turbulence model, especially in the cloud-top region. Consequently, over the past few decades considerable effort has been devoted to developing turbulence models that are better able to parameterize these processes. Much of this work has involved taking parameterizations developed for neutral boundary layers and deriving corrections to account for buoyancy effects associated with the background stratification and local buoyancy sources due to radiative and latent heat transfer within the cloud (see Lilly 1962; Deardor 1980a; Mason 1989; MacVean & Mason 1990, for example). In this paper we hope to contribute to this effort by presenting a number of turbulence models in which the model coefficients are calculated dynamically during the simulation rather than being prescribed a priori.
On the effect of boundary layer growth on the stability of compressible flows
NASA Technical Reports Server (NTRS)
El-Hady, N. M.
The method of multiple scales is used to describe a formally correct method based on the nonparallel linear stability theory, that examines the two and three dimensional stability of compressible boundary layer flows. The method is applied to the supersonic flat plate layer at Mach number 4.5. The theoretical growth rates are in good agreement with experimental results. The method is also applied to the infinite-span swept wing transonic boundary layer with suction to evaluate the effect of the nonparallel flow on the development of crossflow disturbances.
Studies of planetary boundary layer by infrared thermal imagery
NASA Astrophysics Data System (ADS)
Albina, Bogdan; Cazacu, Marius Mihai; Timofte, Adrian; Dimitriu, Dan Gheorghe; Gurlui, Silviu Octavian
The IR camera is a relatively novel device for remote sensing of atmospheric thermal processes from the Planetary Boundary Layer (PBL) based on measurements of the infrared radiation. Infrared radiation is energy radiated by the motion of atoms and molecules on the surface of aerosols, when their temperature is more than absolute zero. The IR camera measures directly the intensity of radiation emitted by aerosols which is converted by an imaging sensor into an electric signal, resulting a thermal image. Every image pixel that corresponds to a specific radiance is pre-processed to identify the brightness temperature. The thermal infrared imaging radiometer used in this study, NicAir, is a precision radiometer developed by Prata et al. The device was calibrated for the temperature range of 270-320 K and using a calibration table along with image processing software, important information about variations in temperature can be extracted from acquired IR images. The PBL is the lowest layer of the troposphere where the atmosphere interacts with the ground surfaces. The importance of PBL lies in the fact that it provides a finite but varying volume in which pollutants can disperse. The aim of this paper is to analyze the PBL altitude and thickness variations over Iasi region using the IR imaging camera as well as its behavior from day to night and thermal processes occurring in PBL.
Unattended automatic monitoring of boundary layer structures with cost effective lidar ceilometers
NASA Astrophysics Data System (ADS)
M�nkel, Christoph; Roininen, Reijo
The vertical temperature and moisture distribution affect the layering of the atmospheric boundary layer and the existence of inversions within this layer or on the top of it. These layers have a strong influence on the development of episodes of high concentrations of air pollutants which might be harmful to people and ecosystems. The height of the mixing layer is defined as the height up to which due to the thermal structure of the boundary layer vertical dispersion by turbulent mixing of air pollutants takes place. Most of the aerosol particles in an atmospheric column are usually confined to atmospheric layers below this height, the knowledge on the mixing layer height can thus be employed to convert column-mean optical depths measured from satellites into near-surface air quality information. Eye-safe lidar ceilometers are reliable tools for unattended boundary layer structure monitoring around the clock up to heights exceeding 2500 m. Comparison to temperature, humidity, and wind profiles reported by RASS, sodar, radio soundings, and weather mast in-situ sensors has confirmed their ability to detect convective or residual layers. In addition, ceilometers with a single lens optical design enable precise assessment of inversion layers and nocturnal stable layers below 200 m. This design has been chosen for the Vaisala Ceilometer CL31, the standard cloud height indicator for the Automated Surface Observing System of the US National Weather Service (NWS). During a two years evaluation period, the NWS permanently collected backscatter profiles from at least three ceilometers at its test site in Sterling, VA. Based on these and on data from units running at the Vaisala test sites in Vantaa, Finland, and Hamburg, Germany, an automatic algorithm for online retrieval of aerosol layer heights within the boundary layer has been developed that covers not only ideal boundary layer diurnal evolution, but all situations involving clouds, fog, and precipitation. This algorithm is part of the Vaisala boundary layer reporting and analysis tool BL-VIEW. The algorithm is based on the gradient method looking for gradient minima of the backscatter intensity to mark upper edges of aerosol layers. Main additional features of the novel automatic algorithm are a cloud, fog and precipitation filter designed to avoid false hits, a noise and range dependant averaging scheme, and a variable detection threshold. Examples covering a variety of meteorological situations in all seasons will be presented that demonstrate the quality of the algorithm and its application in the field of air quality forecasting.
Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-attachment along the Suction Surface of a Low Pressure Turbine Blade
NASA Technical Reports Server (NTRS)
Ozturk, B.; Schobeiri, M. T.; Ashpis, David E.
The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.
Spatial structures and scaling in the Convective Boundary Layer
NASA Astrophysics Data System (ADS)
Badas, M. G.; Querzoli, G.
We performed an investigation on spatial features of the Convective Boundary Layer (CBL) of the atmosphere, which was simulated in a laboratory model and analyzed by means of image analysis techniques. This flow is dominated by large, anisotropic vortical structures, whose spatial organization affects the scalar transport and therefore the fluxes across the boundary layer. With the aim of investigating the spatial structure and scaling in the Convective Boundary Layer, two-dimensional velocity fields were measured, on a vertical plane, by means of a pyramidal Lucas-Kanade algorithm. The coherent structures characterizing the turbulent convection were educed by analyzing the Finite-Time Lyapunov Exponent fields, which also revealed interesting phenomenological features linked to the mixing processes occurring in the Convective Boundary Layer. Both velocity and vorticity fields were analyzed in a scale-invariance framework. Data analysis showed that normalized probability distribution functions for velocity differences are dependent on the scale and tend to become Gaussian for large separations. Extended Self Similarity holds true for velocity structure functions computed within the mixing layer, and their scaling exponents are interpreted well in the phenomenological framework of the Hierarchical Structure Model. Specifically, ? parameter, which is related to the similarity between weak and strong vortices, reveals a higher degree of intermittency for the vertical velocity component with respect to the horizontal one. On the other hand, the analysis of circulation structure functions shows that scaling exponents are fairly constant in the lowest part of the mixed layer, and their values are in agreement with those reported in Benzi et al. (Phys Rev E 55:3739-3742, 1997) for shear turbulence. Moreover, the relationship between circulation and velocity scaling exponents is analyzed, and it is found to be linear in the bottom part of the mixing layer. The investigation of the CBL spatial features, which has seldom been studied experimentally, has important implications for the comprehension of the mixing dynamics, as well as in turbulence closure models.
Boundary-Layer Meteorol (2009) 132:129149 DOI 10.1007/s10546-009-9380-8
Port�-Agel, Fernando
integrity of the wind turbines. In fact, the ability to predict the spatial distribu- tion of the mean-Tunnel Investigation of Wind-Turbine Wakes: Boundary-Layer Turbulence Effects Leonardo P. Chamorro � Fernando Port� to study turbulence in the wake of a model wind turbine placed in a boundary layer developed over rough
Turbulent boundary-layer along a streamwise bar of a rectangular cross section placed on a flat plate
Y. Furuya; I. Nakamura; M. Miyata; Y. Yama
The three-dimensional turbulent boundary layer developing along a long streamwise bar of a rectangular cross section placed on a flat plate was investigated experimentally. The mean velocity, turbulence intensity and wall shear stress distributions were measured, and the general behavior of the secondary currents accompanying the boundary layer were speculated from the deformation lines of constant velocity and constant turbulence
3D Steady and Unsteady Bifurcations in a Shock-wave\\/Laminar Boundary Layer Interaction: A Numerical Study
J.-Ph. Boin; J. Ch. Robinet; Ch. Corre; H. Deniau
The principal objective of this paper is to study some unsteady characteristics of an interaction between an incident oblique shock wave impinging a laminar boundary layer developing on a plate plane. More precisely, this paper shows that some unsteadiness, in particular the low frequency unsteadiness, originate in a supercritical Hopf bifurcation related to the dynamics of the separated boundary layer
The role of subsidence in a weakly unstable marine boundary layer: a case study
NASA Astrophysics Data System (ADS)
Mazzitelli, I. M.; Cassol, M.; Miglietta, M. M.; Rizza, U.; Sempreviva, A. M.; Lanotte, A. S.
The diurnal evolution of a cloud free, marine boundary layer is studied by means of experimental measurements and numerical simulations. Experimental data belong to an investigation of the mixing height over inner Danish waters. The mixed-layer height measured over the sea is generally nearly constant, and does not exhibit the diurnal cycle characteristic of boundary layers over land. A case study, during summer, showing an anomalous development of the mixed layer under unstable and nearly neutral atmospheric conditions, is selected in the campaign. Subsidence is identified as the main physical mechanism causing the sudden decrease in the mixing layer height. This is quantified by comparing radiosounding profiles with data from numerical simulations of a mesoscale model, and a large-eddy simulation model. Subsidence not only affects the mixing layer height, but also the turbulent fluctuations within it. By analyzing wind and scalar spectra, the role of subsidence is further investigated and a more complete interpretation of the experimental results emerges.
The bottom boundary layer of the deep ocean
Laurence Armi; Robert C. Millard
Some aspects of the bottom boundary layer of the deep ocean are exhibited in profiles of salinity and temperature made with a Woods Hole Oceanographic Institution\\/Brown CTD microprofiler. Profiles from the center of the Hatteras Abyssal Plain have a signature that is characteristic of mixing up a uniformly stratified region. Over rough or sloping topography, to the east and west
The structure of turbulent boundary layers along mildly curved surfaces
B. R. Ramaprian; B. G. Shivaprasad
The structure of turbulence in boundary layers along mildly curved convex and concave surfaces is studied. Measurements of turbulent energy balance, autocorrelations, auto- and cross-power spectra, amplitude probability distributions, and conditional correlations are reported. It is observed that even mild curvature has very strong effects on the various aspects of the turbulent structure. For example, convex curvature suppresses the diffusion
Turbulence measurements in boundary layers along mildly curved surfaces
B. G. Shivaprasad; B. R. Ramaprian
This paper presents results of turbulence measurements in boundary layers over surfaces of mild longitudinal curvature. The study indicates that convex wall curvature decreases both the length and velocity scales of turbulent motions, whereas concave curvature has the opposite effect. While being qualitatively similar to those brought about by stronger wall curvature, mild curvature effects are found to be much
Modelling hyporheic exchange: From the boundary layer to the basin
Marusic, Ivan
Modelling hyporheic exchange: From the boundary layer to the basin M.J. Stewardson a , S.B. Grant a processes at the basin-scale including nutrient cycling and retention; movements of organisms to complete hydrological connectivity at the basin-scale but this is not true for the vertical dimension. Understanding
Critical Averaging Time for Atmospheric Boundary Layer Fluxes
H. Holmes
Calculation of heat and momentum fluxes in the Atmospheric Boundary Layer (ABL) requires separating the turbulent signal into mean and fluctuating components. Since the ABL is not statistically stationary, separation of these components depends on the inherent scales of motion in the flow. A new method is presented that utilizes energy spectra and cospectra analyses of raw velocity and temperature
Evidence of reactive iodine chemistry in the Arctic boundary layer
Anoop S. Mahajan; Marvin Shaw; Hilke Oetjen; Karen E. Hornsby; Lucy J. Carpenter; Lars Kaleschke; Xiangshan Tian-Kunze; James D. Lee; Sarah J. Moller; Peter Edwards; Roisin Commane; Trevor Ingham; Dwayne E. Heard; John M. C. Plane
Although it has recently been established that iodine plays an important role in the atmospheric chemistry of coastal Antarctica, where it occurs at levels which cause significant ozone (O3) depletion and changes in the atmospheric oxidising capacity, iodine oxides have not previously been observed conclusively in the Arctic boundary layer (BL). This paper describes differential optical absorption spectroscopy (DOAS) observations
Turbulent dispersion in the Atmospheric Convective Boundary Layer
A. Dosio
The dispersion of a plume in the Atmospheric Boundary Layer is a very complex phenomenon that includes the transport, the mixing and the chemical transformations of the plume material. When a plume is dispersed in the ABL, its shape, evolution, and internal structure are determined by the interaction between the plume and the turbulent eddies that characterize the atmospheric motion.
Simulations of Serpentine Plasma Actuators in a Laminar Boundary Layer
Roy, Subrata
Simulations of Serpentine Plasma Actuators in a Laminar Boundary Layer Mark Riherd and Subrata Roy to the addition of the serpentine actuation are also measured. Nomenclature u, v, w Flow velocities p Pressure U geometry actuator,17,18 and the serpentine geometry actuator.18 The geometry relevant to the present work
Transition correlations in three-dimensional boundary layers
NASA Astrophysics Data System (ADS)
Reed, Helen L.; Haynes, Timothy S.
The stability and transition characteristics of three-dimensional boundary-layer flows are examined. First, the flow over a rotating cone is considered computationally. An increase of stagnation temperature is found to be only slightly stabilizing. Parameter studies on the simple rotating-cone geometry provide a large database of three-dimensional boundary-layer profiles and associated stability characteristics. To determine the possibility of correlating transition location with parameters based purely on basic-state three-dimensional boundary-layer profile characteristics, an empirical transition location of N = 9 is assumed. Transition location does not correlate with the traditional crossflow Reynolds number. A more appropriate definition for crossflow Reynolds number is found and termed R(sub cf). This new parameter appears to correlate for transition location when plotted against maximum crossflow velocity. Then, the flow over a yawed cone is considered experimentally. The correlation results obtained from the rotating-cone work are applied to the actual measured transition locations on two different yawed-cone models under various angle-of-attack conditions in two different experimental facilities and are verified. This correlation is only suggested as a tool for preliminary transition prediction and design in three-dimensional boundary layers; once a preliminary shape is selected, further linear stability theory or parabolized stability equation calculations are strongly urged.
Transition correlations in three-dimensional boundary layers
NASA Astrophysics Data System (ADS)
Reed, Helen L.; Haynes, Timothy S.
The stability and transition characteristics of three-dimensional boundary-layer flows are examined. First, the flow over a rotating cone is considered computationally. An increase of stagnation temperature is found to be only slightly stabilizing. Parameter studies on the simple rotating-cone geometry provide a large database of three-dimensional boundary-layer profiles and associated stability characteristics. To determine the possibility of correlating transition location with parameters based purely on basic-state three-dimensional boundary-layer profile characteristics, an empirical transition location of N = 9 is assumed. Transition location does not correlate with the traditional crossflow Reynolds number. A more appropriate definition for crossflow Reynolds number is found and termed R(sub cf(new)). This new parameter appears to correlate for transition location when plotted against maximum crossflow velocity. Then, the flow over a yawed cone is considered experimentally. The correlation results obtained from the rotating-cone work are applied to the actual measured transition locations on two different yawed-cone models under various angle-of-attack conditions in two different experimental facilities and are verified. This correlation is only suggested as a tool for preliminary transition prediction and design in three-dimensional boundary layers; once a preliminary shape is selected, further linear stability theory or parabolized stability equation calculations are strongly urged.
Boundary layer effects above a Himalayan valley near Mount Everest
Fanglin Sun; Yaoming Ma; Maoshan Li; Weiqiang Ma; Hui Tian; Stefan Metzger
Periodical Wind Profiler and Radio Acoustic Sounding System observations have been commenced at the Himalayas' northern slope nearby Mount Everest in September 2005. Primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions. Substantial findings include the detection of two wind shears and
Determination of Stability and Translation in a Boundary Layer
NASA Technical Reports Server (NTRS)
Crepeau, John; Tobak, Murray
Reducing the infinite degrees of freedom inherent in fluid motion into a manageable number of modes to analyze fluid motion is presented. The concepts behind the center manifold technique are used. Study of the Blasius boundary layer and a precise description of stability within the flow field are discussed.
The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...
Effects of surface wave breaking on the oceanic boundary layer
Hailun He; Dake Chen
Existing laboratory studies suggest that surface wave breaking may exert a significant impact on the formation and evolution of oceanic surface boundary layer, which plays an important role in the ocean-atmosphere coupled system. However, present climate models either neglect the effects of wave breaking or treat them implicitly through some crude parameterization. Here we use a one-dimensional ocean model (General
Vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds
Virendra P. Ghate; Bruce A. Albrecht; Pavlos Kollias
Continental boundary layer (BL) stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the BL. Vertical velocity structure of these clouds is studied using data from the Atmospheric Radiation Measurement Program's Southern Great Plains observing facility located near Lamont, Oklahoma. Data from
CFD simulation of the atmospheric boundary layer: wall function problems
Bert Blocken; Ted Stathopoulos; Jan Carmeliet
Accurate Computational Fluid Dynamics (CFD) simulations of atmospheric boundary layer (ABL) flow are essential for a wide variety of atmospheric studies including pollutant dispersion and deposition. The accuracy of such simulations can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type
An Asymptotic Description of the Attached, Turbulent, Oscillatory Boundary Layer
M. J. Butler; P. W. Duck; P. K. Stansby
The attached, temporally-oscillating turbulent boundary layer is investigated by use of asymptotic matching techniques, valid for the limit of large Reynolds numbers. Much of the analysis is applicable to generally accepted turbulence models (which satisfy a few basic assumptions as detailed in the paper), and this is then applied in particular to two well established turbulence models, namely the k
CFD simulation of the atmospheric boundary layer: wall function problems
Bert Blocken; Ted Stathopoulos; Jan Carmeliet
Accurate Computational Fluid Dynamics (CFD) simulations of atmospheric boundary layer (ABL) flow are essential for a wide variety of atmospheric studies including pollutant dispersion and deposition. The accuracy of such simulations can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type
Turbulent boundary layer on a mildly curved convex surface
M. M. Gibson; C. A. Verriopoulos
Extensive single point turbulence measurements made in the boundary layer on a mildly curved heated convex wall show that the turbulence heat fluxes and Stanton number are more sensitive to a change in wall curvature than the Reynolds stresses and skinfriction coefficient, and that downstream, as the flow adjusts to new curved conditions, the St\\/cf ratio of Reynolds analogy is
Laminarization of Turbulent Boundary Layer on Flexible and Rigid Surfaces
NASA Technical Reports Server (NTRS)
Maestrello, Lucio
An investigation of the control of turbulent boundary layer flow over flexible and rigid surfaces downstream of a concave-convex geometry has been made. The concave-convex curvature induces centrifugal forces and a pressure gradient on the growth of the turbulent boundary layer. The favorable gradient is not sufficient to overcome the unfavorable; thus, the net effect is a destabilizing, of the flow into Gortler instabilities. This study shows that control of the turbulent boundary layer and structural loading can be successfully achieved by using localized surface heating because the subsequent cooling and geometrical shaping downstream over a favorable pressure gradient is effective in laminarization of the turbulence. Wires embedded in a thermally insulated substrate provide surface heating. The laminarized velocity profile adjusts to a lower Reynolds number, and the structure responds to a lower loading. In the laminarization, the turbulent energy is dissipated by molecular transport by both viscous and conductivity mechanisms. Laminarization reduces spanwise vorticity because of the longitudinal cooling gradient of the sublayer profile. The results demonstrate that the curvature-induced mean pressure gradient enhances the receptivity of the flow to localized surface heating, a potentially viable mechanism to laminarize turbulent boundary layer flow; thus, the flow reduces the response of the flexible structure and the resultant sound radiation.
Detection of boundary-layer transitions in wind tunnels
NASA Technical Reports Server (NTRS)
Wood, W. R.; Somers, D. M.
Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent boundary-layer transitions on wind-tunnel models. Technique allows measurements above or below atmospheric pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.
Large-Scale Streamwise Turbulent Structures in Hypersonic Boundary Layers
English, Benjamin L.
Velocimetry in a M = 4.9 blow-down wind tunnel accompanied by a series of data analysis in order to identify the existence of streamwise-elongated large-scale turbulence structures in a hypersonic boundary layer. Furthermore, this study identified physical...
Atmospheric boundary layer studies in FIFE - Challenges and advances
NASA Technical Reports Server (NTRS)
Kelly, Robert D.
A review is presented of a number of other articles concerning the atmospheric boundary layer (ABL) that focus on challenges and progress in experimental design and analysis represented by those studies. The articles address problems posed by the experimental site itself (inhomogeneity of terrain, size, and vegetation) and examine relationships between the ABL and remote sensing measurements.
Current problems in the stratocumulus-topped atmospheric boundary layer
A. G. M. Driedonks; P. G. Duynkerke
Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies.
Study of convective boundary layer (CBL) processes has depended largely upon laboratory analogs for many years. The pioneering work of Willis and Deardorff (1974) and some 35 subsequent papers by the same authors showed that much useful research could be accomplished with a re...
Von K�rm�n's Constant in Atmospheric Boundary Layer Flow: Reevaluated
Ulf H�gstr�m
A field experiment has been carried out with the specific objective in mind to determine the value of von K�rm�n's constant in atmospheric boundary layer flow, and also to investigate its possible dependence on the surface Rossby number Ro0. Data from three field measurement campaigns at Marsta, Sweden, were used in the analysis. Depending on the ground cover: deep snow
A Simulation of the Wangara Atmospheric Boundary Layer Data
Tetsuji Yamada; George Mellor
Previously, the authors have studied a hierarchy of turbulent boundary layer models, all based on the same closure assumptions for the triple turbulence moments. The models differ in complexity by virtue of a systematic process of neglecting certain of the tendency and diffusion terms in the dynamic equations for the turbulent moments. Based on this work a Level 3 model
Prediction of laminar and turbulent boundary layer with rotation
NASA Astrophysics Data System (ADS)
Zhang, Guoqing; Hua, Yaonan; Wu, Chunghua
This paper studies the laminar and turbulent boundary layer with rotation in a two-dimensional rotating channel by using varying steps, staggered grids, and an implicit central difference scheme. Six computational examples show that the predicted data and the measured ones match quite well. The paper also discusses modifying the turbulence model with rotation.
Passive Control of Supersonic Rectangular Jets through Boundary Layer Swirl
NASA Astrophysics Data System (ADS)
Han, Sang Yeop; Taghavi, Ray R.; Farokhi, Saeed
Mixing characteristics of under-expanded supersonic jets emerging from plane and notched rectangular nozzles are computationally studied using nozzle exit boundary layer swirl as a mean of passive flow control. The coupling of the rectangular jet instability modes, such as flapping, and the swirl is investigated. A three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) code with shock adaptive grids is utilized. For plane rectangular nozzle with boundary layer swirl, the flapping and spanwise oscillations are captured in the jet's small and large dimensions at twice the frequencies of the nozzles without swirl. A symmetrical oscillatory mode is also observed in the jet with double the frequency of spanwise oscillation mode. For the notched rectangular nozzle with boundary layer swirl, the flapping oscillation in the small jet dimension and the spanwise oscillation in the large jet dimension are observed at the same frequency as those without boundary layer swirl. The mass flow rates in jets at 11 and 8 nozzle heights downstream of the nozzles increased by nearly 25% and 41% for the plane and notched rectangular nozzles respectively, due to swirl. The axial gross thrust penalty due to induced swirl was 5.1% for the plane and 4.9% for the notched rectangular nozzle.
The effect of tangential blowing on boundary-layer profiles
Olson, Milford Eugene
in the boundary layer without blowing (f. p. s. ) u - u 0 ix 11S'2 t&B HVH&' Obg (CCH'2 i&F&&gn) Uco Free st& ca&, velocity (f . p. s. ) Bionic. sloi jet velocity (f. p. s. ) Bl owang slui w& dtll (ln. ) Hor zoot al di stance (in. or f i . ) Veriical...
Flat plate turbulent boundary-layer control using vertical LEBUs
NASA Astrophysics Data System (ADS)
Kornilov, V. I.; Boiko, A. V.
Necessity of aerodynamic drag reduction of aircrafts and other moving objects stimulates researchers for finding out new means of the near-wall turbulence control. In [1] it has been found that the vertical positioning of the LEBUs in boundary layer can be much more efficient compared to the conventional horizontal one, although, according to the same authors, the devices were far from being optimized. Present work is focused upon the study of possibility of turbulent skin-friction reduction using flow-aligned vertical LEBUs, the LEBUs being mounted perpendicular to the flat plate surface in nominally gradient-free incompressible turbulent boundary layer. The Reynolds number based on the momentum thickness of the boundary layer at the LEBUs' position was 1099. All measurements were performed using a computer-controlled automated system of space/time hot wire visualization of mean and fluctuating components of the velocity field. The system provided accuracy not worse than approximately �2 �m along x, y, and z coordinates. Local skin friction C f in the regular (unmodified) shear flow was determined from the condition of the best correspondence between measured and and classic velocity coefficient profiles in the region of the law of the wall functionality U^+ = A log y+ + B with known coefficients A and B. In the modified boundary layer C f was determined by the mean velocity gradient at the wall (partial U/partial y)_{y=0}. The measurement technique is given in more detail in [2].
Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Grosch, C. E.; Gatski, T. B. (Technical Monitor)
The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.
Effects of mesoscale surface inhomogeneities on atmospheric boundary layer transfer
Shaw, W.J.; Doran, J.C.; Hubbe, J.M.
Defining the nature of turbulent transfer over horizontally inhomogeneous surfaces remains one of the challenges in meteorology. Because the transfer of energy and momentum through the atmospheric boundary layer forms part of the lower boundary condition for global climate models (GCMs), the problem is important. Over the last two decades, advances in sensor and computer technology wave made good point measurements of turbulent fluxes fairly routine. A fundamental question with respect to climate models, however, is how such point measurements are related to average fluxes over the area of a GCM grid box. In this paper we will use data from the field program to depict the evolution of the boundary layer over adjacent, sharply contrasting surface types on two separate occasions. We will then use simple scaling based on the observations to argue that sub-gridscale motions would often be likely to significantly alter the estimates and resulting parameterizations of GCM-scale surface fluxes in the region.
Atmospheric controls on soil moisture-boundary layer interactions
NASA Astrophysics Data System (ADS)
Findell, Kirsten Lynn
This thesis addresses the question of how the early morning atmospheric thermodynamic structure affects the interaction between the soil moisture state and the growth and development of the boundary layer (BL), leading to the triggering of convection. It is concluded that in mid-latitudes, for matters of convective triggering and response to land surface conditions, the critical portion of the atmosphere-approximately 1 to 3 km above the ground surface-is independent of geographic location and local synoptic setting. As long as the low levels of the troposphere are relatively humid but not extremely close to saturation, a negative feedback between soil moisture and rainfall is likely when the early morning temperature lapse rate in this region is dry adiabatic; a positive feedback is likely when it is moist adiabatic; and when there is a temperature inversion in this region, deep convection cannot occur, independent of the soil moisture. Additionally, when the low levels of the troposphere are extremely dry or very close to saturation, the occurrence of convection is determined solely by the atmospheric conditions. Essential characteristics of the temperature structure of the early-morning atmosphere are captured by a new thermodynamic measure, the Convective Triggering Potential (CTP), developed to distinguish between soundings favoring rainfall over dry soils from those favoring rainfall over wet soils. A one-dimensional model of the planetary boundary layer (BL) and surface energy budget has been modified to allow the growing BL to entrain air from an observed atmospheric sounding. The model is used to analyze the impact of soil saturation on BL development and the triggering of convection in different atmospheric settings. Analyses of CTP-HIlow scatter plots from radiosonde stations across the contiguous 48 United States reveal that positive feedbacks are likely in much of the eastern half of the country. Use of the 1D BL model at four additional stations confirms that the CTP-HI low framework used in this nationwide analysis is valid for regions far removed from Illinois, where it was originally developed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.) (Abstract shortened by UMI.)
Vertical variations of boundary layer chemistry in the urban environment of Boston
NASA Astrophysics Data System (ADS)
Wang, S.; Geyer, A.; Stutz, J.
Boundary layer chemistry in urban areas is often strongly influenced by surface emissions of NOx and VOCs. Vertical mixing in combination with chemical transformations leads to distinctive vertical profiles of reactive trace gases. Chemistry, therefore, varies with altitude in the lowest 50 m, in particular in the stable nocturnal boundary layer. The influence of vertical mixing on chemistry in the lowest part of the boundary layer is often not accurately described, and a better understanding is needed to improve our ability to model urban air pollution. During the NEAQS/NAOPEX field campaign in July-August, 2002, vertical distributions of NO2, O3, HONO, HCHO, NO3, and several other trace gases were measured in the lowest 10 - 50 m of the atmosphere with a long-path differential optical absorption spectroscopy instrument in a residential area in Boston, MA. Various meteorological parameters were also monitored at the same location. Clear vertical trace gas concentration gradients were observed. In particular, during nights with strong stabilities, nocturnal boundary layer chemistry was clearly altitude dependent. Positive gradients of O3 and NO3 developed as a result of the fast chemical reactions with NO emitted at the surface. Negative NO2 and HONO gradients point to the vertical variation of the heterogeneous NO2-HONO conversion process, suggesting the importance of heterogeneous chemistry at the ground and building walls. With the transition from the stable boundary layer to a convective layer after sunrise, the vertical profiles regressed. However, vertical gradients of HCHO and O3 were observed in the afternoon on most days of this study. The observations suggest that ground-based emissions and fast photochemistry can lead to vertical profiles of trace gases in an urban boundary layer even during daytime. The vertical stratification of boundary layer chemistry, which depends on many factors including mixing strength, fast photochemistry and the emission strength, will be discussed.
Environmental boundaries to energy development
Trivelpiece, A.W.
Public concern about the environment, health and safety consequences of energy technology has been growing steadily for more than two decades in the United States. This concern forms an important boundary condition as the United States seeks to develop a new National Energy Strategy. Furthermore, the international aspects of the energy/environment interface such as acid rain global climate change and stratospheric ozone depletion are very prominent in US thinking. In fact, the energy systems of the world are becoming more closely coupled environmentally and otherwise. Now where is this coupling more important than that between the industrialized and developing world; the choices made by each will have profound effects on the other. The development of energy technologies compatible with both economic growth and improving and sustaining environmental quality represents a major R D challenge to the US and USSR. Decision about adoption of new technology and R D priorities can be improved by better measurements of how energy sources and uses are changing throughout the world and better methods to project the potential consequences of these decisions. Such projection require understanding relative risks of alternating existing and evolving technologies. All of these R D areas, technology improvement energy system monitoring and projection and comparative risk assessment are the topics of this seminar. Progress in each may be enhanced by collaboration and cooperation between our two countries. 7 refs., 27 figs., 5 tabs.
A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers
NASA Technical Reports Server (NTRS)
Tetervin, Neal; Lin, Chia Chiao
A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.
Linear segmentation algorithm for detecting layer boundary with lidar.
Mao, Feiyue; Gong, Wei; Logan, Timothy
The automatic detection of aerosol- and cloud-layer boundary (base and top) is important in atmospheric lidar data processing, because the boundary information is not only useful for environment and climate studies, but can also be used as input for further data processing. Previous methods have demonstrated limitations in defining the base and top, window-size setting, and have neglected the in-layer attenuation. To overcome these limitations, we present a new layer detection scheme for up-looking lidars based on linear segmentation with a reasonable threshold setting, boundary selecting, and false positive removing strategies. Preliminary results from both real and simulated data show that this algorithm cannot only detect the layer-base as accurate as the simple multi-scale method, but can also detect the layer-top more accurately than that of the simple multi-scale method. Our algorithm can be directly applied to uncalibrated data without requiring any additional measurements or window size selections. PMID:24216909
Characteristics of nonlinear evolution of wavepackets in boundary layers
NASA Astrophysics Data System (ADS)
Yu, Min; Luo, JiSheng; Li, Jia
The nonlinear evolution of a finite-amplitude disturbance in a 3-D supersonic boundary layer over a cone was investigated recently by Liu et al. using direct numerical simulation (DNS). It was found that certain small-scale 3-D disturbances amplified rapidly. These disturbances exhibit the characteristics of second modes, and the most amplified components have a well-defined spanwise wavelength, indicating a clear selectivity of the amplification. In the case of a cone, the three-dimensionality of the base flow and the disturbances themselves may be responsible for the rapid amplification. In order to ascertain which of these two effects are essential, in this study we carried out DNS of the nonlinear evolution of a spanwise localized disturbance (wavepacket) in a flat-plate boundary layer. A similar amplification of small-scale disturbances was observed, suggesting that the direct reason for the rapid amplification is the three-dimensionality of the disturbances rather than the three-dimensional nature of the base flow, even though the latter does alter the spanwise distribution of the disturbance. The rapid growth of 3-D waves may be attributed to the secondary instability mechanism. Further simulations were performed for a wavepacket of first modes in a supersonic boundary layer and of Tollmien-Schlichting (T-S) waves in an incompressible boundary layer. The results show that the amplifying components are in the band centered at zero spanwise wavenumber rather than at a finite spanwise wavenumber. It is therefore concluded that the rapid growth of 3-D disturbances in a band centered at a preferred large spanwise wavenumber is the main characteristic of nonlinear evolution of second mode disturbances in supersonic boundary layers.
Gasdynamic simulations of the solar wind interaction with Venus - Boundary layer formation
NASA Astrophysics Data System (ADS)
McGary, J. E.
A 2D gasdynamic simulation of the mass-loaded solar wind flow around the dayside of Venus is presented. For average ionopause conditions near 300 km, the simulations show that mass loading from the pickup of oxygen ions produces a boundary layer of finite thickness along the ionopause. Within this layer and toward the ionopause, the temperature decreases and the total mass density increases significantly. Furthermore, there is a shear in the bulk flow velocity across the boundary layer, such that the tangential flow decreases in speed as the ionopause is approached and remains low along the ionopause which is consistent with Pioneer Venus observations. Numerical simulations are carried out for various mass addition rates and demonstrate that the boundary layer develops when oxygen ion production exceeds approximately 2 x 10 exp 5/cu m per s.
Ceilometer observations of the boundary layer over Warsaw, Poland
NASA Astrophysics Data System (ADS)
Stachlewska, Iwona S.; Pi?d?owski, Micha?; Migacz, Szymon; Szkop, Artur; Zieli?ska, Anna J.; Swaczyna, Pawe? L.
Jenoptik's CHM 15k ceilometer was used to monitor the vertical structure of the atmospheric boundary layer (ABL) over Warsaw, from 2008 until 2011, on Mondays and Thursdays, in 24h periods. Hereby, we present an assessment of the signal-to-noise ratio along with a sensitivity study of signal smoothing methods developed in-house. With the proposed averaging, ceilometer attenuated-backscatter signals reached the high troposphere, which makes this sensor competitive to a single-wavelength elastic lidar. The smoothed signals were employed as an input for algorithms developed to automatically detect the ABL height, clouds, fog, and precipitation in the lower troposphere. The classification of weather conditions was validated by the METAR reports from the Warsaw Airport. The obtained ABL heights were compared to those assessed from radio-soundings from a nearby meteorological station WMO12374 in Legionowo. An inter-comparison of the ABL heights, derived by using the Jenoptik's automated routine against the in-house developed algorithms, is in favor of the latter. The presented four annual cycles of the ABL height, obtained with various derivative-based methods, are the first such long-term results reported using the CHM 15k sensor in Eastern Europe.
The effect of concave surface curvature on turbulent boundary layers
NASA Astrophysics Data System (ADS)
Hoffmann, P. H.; Muck, K. C.; Bradshaw, P.
The response of a turbulent boundary layer to suddenly applied concave surface curvature is investigated. The main conclusion of this and the companion paper by Muck, Hoffmann and Bradshaw (1985) is that the effects of concave (destabilizing) and convex (stabilizing) curvature on boundary layers - and presumably on other shear layers - are totally different, even qualitatively. As shown in Muck, Hoffmann and Bradshaw (1985), convex curvature tends to attenuate the pre-existing turbulence and, at least in the case of mild curvature, there are no large changes in statistical average shape. Concave curvature, on the other hand, can lead to the quasi-inviscid generation of longitudinal ('Taylor-Goertler') vortices, and it is shown that significant changes in the turbulence structure are induced both directly by the curvature and indirectly by the vortices.
On buffer layers as non-reflecting computational boundaries
NASA Technical Reports Server (NTRS)
Hayder, M. Ehtesham; Turkel, Eli L.
We examine an absorbing buffer layer technique for use as a non-reflecting boundary condition in the numerical simulation of flows. One such formulation was by Ta'asan and Nark for the linearized Euler equations. They modified the flow inside the buffer zone to artificially make it supersonic in the layer. We examine how this approach can be extended to the nonlinear Euler equations. We consider both a conservative and a non-conservative form modifying the governing equations in the buffer layer. We compare this with the case that the governing equations in the layer are the same as in the interior domain. We test the effectiveness of these buffer layers by a simulation of an excited axisymmetric jet based on a nonlinear compressible Navier-Stokes equations.
Mass transfer dominated by thermal diffusion in laminar boundary layers
NASA Astrophysics Data System (ADS)
Garc�a-Ybarra, Pedro L.; Castillo, Jose L.
The concentration distribution of massive dilute species (e.g. aerosols, heavy vapours, etc.) carried in a gas stream in non-isothermal boundary layers is studied in the large-Schmidt-number limit, Sc[dbl greater-than sign]1, including the cross-mass-transport by thermal diffusion (Ludwig Soret effect). In self-similar laminar boundary layers, the mass fraction distribution of the dilute species is governed by a second-order ordinary differential equation whose solution becomes a singular perturbation problem when Sc[dbl greater-than sign]1. Depending on the sign of the temperature gradient, the solutions exhibit different qualitative behaviour. First, when the thermal diffusion transport is directed toward the wall, the boundary layer can be divided into two separated regions: an outer region characterized by the cooperation of advection and thermal diffusion and an inner region in the vicinity of the wall, where Brownian diffusion accommodates the mass fraction to the value required by the boundary condition at the wall. Secondly, when the thermal diffusion transport is directed away from the wall, thus competing with the advective transport, both effects balance each other at some intermediate value of the similarity variable and a thin intermediate diffusive layer separating two outer regions should be considered around this location. The character of the outer solutions changes sharply across this thin layer, which corresponds to a second-order regular turning point of the differential mass transport equation. In the outer zone from the inner layer down to the wall, exponentially small terms must be considered to account for the diffusive leakage of the massive species. In the inner zone, the equation is solved in terms of the Whittaker function and the whole mass fraction distribution is determined by matching with the outer solutions. The distinguished limit of Brownian diffusion with a weak thermal diffusion is also analysed and shown to match the two cases mentioned above.
Remote detection of boundary-layer transition by an optical system
NASA Technical Reports Server (NTRS)
Hall, Robert M.; Azzazy, Medhat; Modarress, Dariush
This instrument development program was funded because of the urgent need to measure boundary-layer transition in wind tunnels. In the course of this development program, a prototype was designed, built, and tested. Recent transonic experiments in the Boeing Model Transonic Wind Tunnel show that the interferometer results correlate very well with sublimating chemical tests.
Scaling Analysis of the Thermal Boundary Layer Adjacent to an Abruptly Heated Inclined Flat Plate
S. C. Saha; C. Lei; J. C. Patterson
The natural convection thermal boundary layer adjacent to an abruptly heated inclined flat plate is investigated through a scaling analysis and verified by numerical simulations. In general, the development of the thermal flow can be characterized by three distinct stages, i.e. a start-up stage, a transitional stage and a steady state stage. Major scales including the flow velocity, flow development
Boundary-Layer Meteorol (2010) 134:367-386 DOI 10.1007/s10546-009-9452-9
Reading, University of
� Synoptically-forced boundary layer 1 Introduction The atmospheric boundary layers is typically thought of underBoundary-Layer Meteorol (2010) 134:367-386 DOI 10.1007/s10546-009-9452-9 The Moist Boundary Layer layer in this transport. We expand a conceptual model of dry boundary-layer structure under synoptic
Transient Heat Transfer in a Semitransparent Radiating Layer with Boundary Convection and Surface Reflections
NASA Technical Reports Server (NTRS)
Siegel, Robert
Surface convection and refractive index are examined during transient radiative heating or cooling of a grey semitransparent layer with internal absorption, emission and conduction. Each side of the layer is exposed to hot or cold radiative surroundings, while each boundary is heated or cooled by convection. Emission within the layer and internal reflections depend on the layer refractive index. The reflected energy and heat conduction distribute energy across the layer and partially equalize the transient temperature distributions. Solutions are given to demonstrate the effect of radiative heating for layers with various optical thicknesses, the behavior of the layer heated by radiation on one side and convectively cooled on the other, and a layer heated by convection while being cooled by radiation. The numerical method is an implicit finite difference procedure with non-uniform space and time increments. The basic method developed in earlier work is expanded to include external convection and incident radiation.
Overview of Boundary Layer Transition Research in Support of Orbiter Return To Flight
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Greene, Francis A.; Kinder, Gerald R.; Wang, K. C.
A predictive tool for estimating the onset of boundary layer transition resulting from damage to and/or repair of the thermal protection system was developed in support of Shuttle Return to Flight. The boundary layer transition tool is part of a suite of tools that analyze the aerothermodynamic environment to the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time (and thus Mach number) at transition onset is predicted to help define the aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local thermal protection system and structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against select flight data. Computed local boundary layer edge conditions were used to correlate the results, specifically the momentum thickness Reynolds number over the edge Mach number and the boundary layer thickness. For the initial Return to Flight mission, STS-114, empirical curve coefficients of 27, 100, and 900 were selected to predict transition onset for protuberances based on height, and cavities based on depth and length, respectively.
Version 2 of the Protuberance Correlations for the Shuttle-Orbiter Boundary Layer Transition Tool
NASA Technical Reports Server (NTRS)
King, Rudolph A.; Kegerise, Michael A.; Berry, Scott A.
Orbiter-specific transition data, acquired in four ground-based facilities (LaRC 20-Inch Mach 6 Air Tunnel, LaRC 31-Inch Mach 10 Air Tunnel, LaRC 20-Inch Mach 6 CF4 Tunnel, and CUBRC LENS-I Shock Tunnel) with three wind tunnel model scales (0.75, 0.90, and 1.8%) and from Orbiter historical flight data, have been analyzed to improve a pre-existing engineering tool for reentry transition prediction on the windward side of the Orbiter. Boundary layer transition (BLT) engineering correlations for transition induced by isolated protuberances are presented using a laminar Navier-Stokes (N-S) database to provide the relevant boundary-layer properties. It is demonstrated that the earlier version of the BLT correlation that had been developed using parameters derived from an engineering boundary-layer code has improved data collapse when developed with the N-S database. Of the new correlations examined, the proposed correlation 5, based on boundary-layer edge and wall properties, was found to provide the best overall correlation metrics when the entire database is employed. The second independent correlation (proposed correlation 7) selected is based on properties within the boundary layer at the protuberance height. The Aeroheating Panel selected a process to derive the recommended coefficients for Version 2 of the BLT Tool. The assumptions and limitations of the recommended protuberance BLT Tool V.2 are presented.
Lidar analysis techniques for use in the atmospheric boundary layer
NASA Technical Reports Server (NTRS)
Eichinger, William E.; Cooper, Daniel I.; Hof, Doug; Holtkamp, David; Quick, Robert, Jr.; Tiee, Joe; Karl, Robert
There is a growing body of observational and theoretical evidence which suggests that local climate characteristics are associated with variations in the earth's surface. The link between surface variability and local-scale processes must be made if we are to improve our understanding of the feedback mechanisms involved in surface-atmosphere dynamics. However, to understand these interactions, the surface-atmosphere interface must be studied as a large-scale spatial system. Lidars are ideal tools to study the spatial properties of the atmosphere. The described techniques were developed for use with the Los Alamos Water Raman-Lidar, but are applicable to many other types of lidar. The methodology of the analysis of lidar data is summarized in order to determine meteorological parameters in the atmospheric boundary layer. The techniques are not exhaustive but are intended to show the depth and breadth of the information which can be obtained from lidars. Two methods for the computation of water-vapor fluxes were developed. The first uses the fact that the water vapor concentration in the vertical direction follows a logarithmic profile when corrected for atmospheric stability. The second method involves using inertial dissipation techniques in which lidar-derived spatial and temporal power spectra are used to determine the flux.
Formation of Structured Dayside Boundary Layers under Different Solar Wind Conditions: THEMIS Observations
NASA Technical Reports Server (NTRS)
Avanov, Levon A.; Chandler, Michael O.
We have begun an investigation of the formation of the dayside low latitude boundary layer under different solar wind conditions using data from the THEMIS spacecraft. We present two cases of magnetopause/LLBL interface crossings made by the five spacecraft; one under long lasting northward IMF and a second for a period of southward IMF. All spacecraft during these observations traversed the dayside magnetosphere in a string-of-pearls configuration with the farthest distance between spacecraft less than approx.2 R(sub E). The sequence of observations from spacecraft, as they crossed the magnetopause, shows the development of a highly structured boundary layer regardless of the polarity of the IMF. We discuss possible scenarios for the development of such structured boundary layers, including low latitude reconnection under northward IMF as well as double reconnection in opposite hemispheres.
Snodar: a new instrument to measure the height of the boundary layer on the Antarctic plateau
Ashley, Michael C. B.
Snodar: a new instrument to measure the height of the boundary layer on the Antarctic plateau Colin boundary layer on the Antarctic plateau is of particular importance to designers of optical telescopes of the atmospheric boundary layer at Dome A and Dome C on the Antarctic plateau. Snodar, or Surface layer Non
Post-doctoral position in atmospheric boundary layer dynamics Analysis of BLLAST field experiment
Post-doctoral position in atmospheric boundary layer dynamics Analysis of BLLAST field experiment. Background: The international BLLAST project (Boundary Layer Late Afternoon and Sunset Turbulence, http the daytime well-mixed, convective boundary layer (CBL), decays to an intermittently turbulent "residual layer
Analysis of modified MYJ and YSU boundary layer schemes in WRF-Chem with respect to simulated boundary layer heights and pollutant concentrations
NASA Astrophysics Data System (ADS)
Forkel, Renate; Foreman, Richard; Emeis, Stefan
To improve the performance of boundary layer schemes currently applied within WRF-Chem (Grell et al., 2005), the Mellor-Yamada-Janjic (MYJ) model (Mellor and Yamada 1982) and the Yonsei University (YSU) PBL scheme (Hong et al. 2006) have been updated using data from a 100 m high offshore measurement tower called FINO1. The turbulence intensity in the Mellor-Yamada-Janjic model has been enhanced as described in Foreman and Emeis (2012). An alternative to the exchange coefficient for stable stratification in the YSU scheme is described in Foreman et al. (2014). These modifications to the two schemes have been applied and are compared with the existing schemes. For example, the updated MYJ scheme results in an improved representation of the turbulent kinetic energy throughout the boundary layer as compared with the measurements at FINO1. The modified MYJ and YSU schemes, which have been originally developed for wind energy applications, have been implemented into version 3.5 of the WRF model. Simulations with WRF-Chem were carried out for Europe and the region of Augsburg in order to evaluate the effect of the modified PBL schemes on simulated PBL heights, gas phase pollutant and aerosol concentrations. Foreman, R.J. and S. Emeis, 2012. A method for increasing the turbulent kinetic energy in the Mellor-Yamada-Janjic boundary layer parametrization. Boundary Layer Meteorology 145:329-349. Foreman, R.J. S. Emeis and B. Canadillas, 2014. Stable boundary layer parametrization without eddy viscosity or turbulent kinetic energy equation approaches. Submitted to Boundary Layer Meteorology 2014. Grell, G. A., Peckham, S. E., Schmitz, R., McKeen, S. A., Frost, G., Skamarock,W. C., and Eder, B., 2005. Fully Coupled Online Chemistry within the WRF Model. Atmospheric Environment 39, 6957-6975. Hong S, Noh Y, Dudhia J 2006. Nonlocal boundary layer vertical diffusion in a medium-range forecast model. Mon Wea Rev 124:2322-2339. Mellor GL, Yamada T 1982. Development of a turbulence closure model for geophysical fluid problems. Rev. Geophys. Space Phys 20:851-875.
Doppler Profiler and Radar Observations of Boundary Layer Variability during the Landfall of Tropical Storm Gabrielle.
NASA Astrophysics Data System (ADS)
Knupp, Kevin R.; Walters, Justin; Biggerstaff, Michael
Detailed observations of boundary layer structure were acquired on 14 September 2001, prior to and during the landfall of Tropical Storm Gabrielle. The Mobile Integrated Profiling System (MIPS) and the Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) were collocated at the western Florida coastline near Venice, very close to the wind center at landfall. Prior to landfall, the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall. The cool air mass was expansive, with an area within the 23�C surface isotherm of about 50 000 km2. East-northeasterly surface flow transported this cool air off the west coast of Florida, toward the convergent warm core of the Gabrielle, and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase.Airflow properties of the boundary layer around the coastal zone are examined using the MIPS and SMART-R data. Wind profiles exhibited considerable temporal variability throughout the period of observations. The stable offshore flow within stratiform precipitation exhibited a modest jet that descended from about 600 to 300 m within the 20-km zone centered on the coastline. In contrast, the onshore flow on the western side of the wind center produced a more turbulent boundary layer that exhibited a well-defined top varying between 400 and 1000 m MSL. The horizontal variability of each boundary layer is examined using high-resolution Doppler radar scans at locations up to 15 km on either side of the coastline, along the mean flow direction of the boundary layer. These analyses reveal that transitions in boundary layer structure for both the stable and unstable regimes were most substantial within 5 km of the coastline.
FOREWORD: International Conference on Planetary Boundary Layer and Climate Change
NASA Astrophysics Data System (ADS)
Djolov, G.; Esau, I.
One of the greatest achievements of climate science has been the establisment of the concept of climate change on a multitude of time scales. The Earth's complex climate system does not allow a straightforward interpretation of dependences between the external parameter perturbation, internal stochastic system dynamics and the long-term system response. The latter is usually referred to as climate change in a narrow sense (IPCC, 2007). The focused international conference "Planetary Boundary Layers and Climate Change" has addressed only time scales and dynamical aspects of climate change with possible links to the turbulent processes in the Planetary Boundary Layer (PBL). Although limited, the conference topic is by no means singular. One should clearly understand that the PBL is the layer where 99% of biosphere and human activity are concentrated. The PBL is the layer where the energy fluxes, which are followed by changes in cryosphere and other known feedbacks, are maximized. At the same time, the PBL processes are of a naturally small scale. What is the averaged long-term effect of the small-scale processes on the long-term climate dynamics? Can this effect be recognized in existing long-term paleo-climate data records? Can it be modeled? What is the current status of our theoretical understanding of this effect? What is the sensitivity of the climate model projections to the representation of small-scale processes? Are there significant indirect effects, e.g. through transport of chemical components, of the PBL processes on climate? These and other linked questions have been addressed during the conference. The Earth's climate has changed many times during the planet's history, with events ranging from ice ages to long periods of warmth. Historically, natural factors such as the amount of energy released from the Sun, volcanic eruptions and changes in the Earth's orbit have affected the Earth's climate. Beginning late in the 18th century, human activities associated with the Industrial Revolution such as the addition of greenhouse gases and aerosols has changed the composition of the atmosphere. These changes are likely to have influenced temperature, precipitation, storms and sea level (IPCC, 2007). However, these features of the climate also vary naturally, so determining what fraction of climate changes are due to natural variability versus human activities is challenging and not yet a solved problem. Africa is vulnerable to climate change as its ability to adaptat and mitigate is considerably dampened (IPCC, 2007). Climate change may impede a nations ability to achieve sustainable development and the Millennium Development Goals, and because of that Africa (particularly sub-tropical Africa) will experience increased levels of water stress and reduced agricultural yields of up to 50% by 2020. An example of the scale of the region's vulnerability was demonstrated during the last very dry year (1991/92) when 30% of the southern African population was put on food aid and more than one million people were displaced. Climate change in Africa is essentially dependent on our understanding of the PBL processes both due to the indispensible role of the atmospheric convection in the African climate and due to its tele-connections to other regions, e.g. the tropical Pacific and Indian monsoon regions. Although numerous publications attribute the observed changes to one or another modification of the convective patterns, further progress is impeded by imperfections of the small-scale process parameterizations in the models. The uncertainties include parameter uncertainties of known physical processes, which could be reduced through better observations/modelling, as well as uncertainties in our knowledge of physical processes themselves (or structural uncertainties), which could be reduced only through theoretical development and design of new, original observations/experiments (Oppenheimer et al., Science, 2007). Arguably, the structural uncertainties is hard to reduce and this could be one of the reasons determinin
Polymer Effects on Heat Transport in Laminar Boundary Layer Flow
Roberto Benzi; Emily S. C. Ching; Vivien W. S. Chu
We consider a laminar Blasius boundary-layer flow above a slightly heated horizontal plate and study the effect of polymer additives on the heat transport. We show that the action of the polymers can be understood as a space-dependent effective viscosity that first increases from the zero-shear value then decreases exponentially back to the zero-shear value as one moves away from the boundary. We find that with such an effective viscosity, both the horizontal and vertical velocities near the plate are decreased thus leading to an increase in the friction drag and a decrease in the heat transport in the flow.
Large-Eddy Simulations and Observations of Atmospheric Marine Boundary Layers above Nonequilibrium Surface Waves
Peter P. Sullivan; James B. Edson; Tihomir Hristov; James C. McWilliams
Winds and waves in marine boundary layers are often in an unsettled state when fast-running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields. A large-eddy simulation (LES) model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low-wind\\/fast-wave regime. It is used to simulate
The calculation of chemically reacting turbulent boundary layers by means of finite chemical kinetics
J. B. Vos
A computer program developed at Delft University of Technology to describe two-dimensional turbulent flows through channels with and without sudden expansion was extended by accounting for heat and mass transfer at the boundaries. The wall-function method of Chieng and Launder (1980) was adapted, allowing the calculation of the Von Karman constant E, which is a function of the local boundary-layer
Simulation and optimal control of wind-farm boundary layers
NASA Astrophysics Data System (ADS)
Meyers, Johan; Goit, Jay
In large wind farms, the effect of turbine wakes, and their interaction leads to a reduction in farm efficiency, with power generated by turbines in a farm being lower than that of a lone-standing turbine by up to 50%. In very large wind farms or `deep arrays', this efficiency loss is related to interaction of the wind farms with the planetary boundary layer, leading to lower wind speeds at turbine level. Moreover, for these cases it has been demonstrated both in simulations and wind-tunnel experiments that the wind-farm energy extraction is dominated by the vertical turbulent transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate the use of optimal control techniques combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large `infinite' wind farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with actuator-disk and actuator-line representations of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind that combines Fourier-spectral discretization in horizontal directions with a fourth-order finite-volume approach in the vertical direction. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in an actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. Optimal model-predictive control (or optimal receding horizon control) is used, where the model simply consists of the full LES equations, and the time horizon is approximately 280 seconds. The optimization is performed using a nonlinear conjugate gradient method, and the gradients are calculated by solving the adjoint LES equations. We find that the extracted farm power increases by approximately 20% when using optimal model-predictive control. However, the increased power output is also responsible for an increase in turbulent dissipation, and a deceleration of the boundary layer. Further investigating the energy balances in the boundary layer, it is observed that this deceleration is mainly occurring in the outer layer as a result of higher turbulent energy fluxes towards the turbines. In a second optimization case, we penalize boundary-layer deceleration, and find an increase of energy extraction of approximately 10%. In this case, increased energy extraction is balanced by a reduction in of turbulent dissipation in the boundary layer. J.M. acknowledges support from the European Research Council (FP7-Ideas, grant no. 306471). Simulations were performed on the computing infrastructure of the VSC Flemish Supercomputer Center, funded by the Hercules Foundation and the Flemish Government.
Structure Identification Within a Transitioning Swept-Wing Boundary Layer
NASA Technical Reports Server (NTRS)
Chapman, Keith; Glauser, Mark
Extensive measurements are made in a transitioning swept-wing boundary layer using hot-film, hot-wire and cross-wire anemometry. The crossflow-dominated flow contains stationary vortices that breakdown near mid-chord. The most amplified vortex wavelength is forced by the use of artificial roughness elements near the leading edge. Two-component velocity and spanwise surface shear-stress correlation measurements are made at two constant chord locations, before and after transition. Streamwise surface shear stresses are also measured through the entire transition region. Correlation techniques are used to identify stationary structures in the laminar regime and coherent structures in the turbulent regime. Basic techniques include observation of the spatial correlations and the spatially distributed auto-spectra. The primary and secondary instability mechanisms are identified in the spectra in all measured fields. The primary mechanism is seen to grow, cause transition and produce large-scale turbulence. The secondary mechanism grows through the entire transition region and produces the small-scale turbulence. Advanced techniques use Linear Stochastic Estimation (LSE) and Proper Orthogonal Decomposition (POD) to identify the spatio-temporal evolutions of structures in the boundary layer. LSE is used to estimate the instantaneous velocity fields using temporal data from just two spatial locations and the spatial correlations. Reference locations are selected using maximum RMS values to provide the best available estimates. POD is used to objectively determine modes characteristic of the measured flow based on energy. The stationary vortices are identified in the first laminar modes of each velocity component and shear component. Experimental evidence suggests that neighboring vortices interact and produce large coherent structures with spanwise periodicity at double the stationary vortex wavelength. An objective transition region detection method is developed using streamwise spatial POD solutions which isolate the growth of the primary and secondary instability mechanisms in the first and second modes, respectively. Temporal evolutions of dominant POD modes in all measured fields are calculated. These scalar POD coefficients contain the integrated characteristics of the entire field, greatly reducing the amount of data to characterize the instantaneous field. These modes may then be used to train future flow control algorithms based on neural networks.
Numerical Solutions of Free Convection Boundary Layer Flow on a Solid Sphere with Convective Boundary Conditions
NASA Astrophysics Data System (ADS)
Alkasasbeh, H. T.; Salleh, M. Z.; Tahar, R. M.; Nazar, R.
The free convection boundary layer flow on a solid sphere with convective boundary conditions has been investigated. The basic equations of boundary layer are transformed into a non-dimensional form and reduced to nonlinear systems of partial differential equations are solved numerically using an implicit finite difference scheme known as the Keller-box method. Numerical results are obtained for the wall temperature, the local heat transfer coefficient and the local skin friction coefficient, as well as the velocity and temperature profiles of the fluid. The features of the flow and heat transfer characteristics for Prandtl number, Pr = 0.7 7 and 100, the conjugate parameter y = 0.05, 0.1, 0.2 and the coordinate running along the surface of the sphere, 0� <= x <= 120� are analyzed and discussed.
Bandgap tunability at single-layer molybdenum disulphide grain boundaries
NASA Astrophysics Data System (ADS)
Huang, Yu Li; Chen, Yifeng; Zhang, Wenjing; Quek, Su Ying; Chen, Chang-Hsiao; Li, Lain-Jong; Hsu, Wei-Ting; Chang, Wen-Hao; Zheng, Yu Jie; Chen, Wei; Wee, Andrew T. S.
Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40�0.05?eV for single-layer, 2.10�0.05?eV for bilayer and 1.75�0.05?eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85�0.05?eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.
Bandgap tunability at single-layer molybdenum disulphide grain boundaries.
Huang, Yu Li; Chen, Yifeng; Zhang, Wenjing; Quek, Su Ying; Chen, Chang-Hsiao; Li, Lain-Jong; Hsu, Wei-Ting; Chang, Wen-Hao; Zheng, Yu Jie; Chen, Wei; Wee, Andrew T S
Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40�0.05?eV for single-layer, 2.10�0.05?eV for bilayer and 1.75�0.05?eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85�0.05?eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering. PMID:25687991
Transport of contaminants in the planetary boundary layer
NASA Technical Reports Server (NTRS)
Lee, I. Y.; Swan, P. R.
A planetary boundary layer model is described and used to simulate PBL phenomena including cloud formation and pollution transport in the San Francisco Bay Area. The effect of events in the PBL on air pollution is considered, and governing equations for the average momentum, potential temperature, water vapor mixing ratio, and air contaminants are presented. These equations are derived by integrating the basic equations vertically through the mixed layer. Characteristics of the day selected for simulation are reported, and the results suggest that the diurnally cyclic features of the mesoscale motion, including clouds and air pollution, can be simulated in a readily interpretable way with the model.
Simulation of the diurnal evolution of the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Ilyushin, B. B.
Results of simulating the diurnal evolution of the atmospheric boundary layer (ABL) with a second-order closure model are presented. The model includes new algebraic expressions for triple correlations to describe their behavior over the entire height of the mixed layer adequately to measurements. The model also takes into account the influence of long-wave radiation on the heat balance, which becomes important in the nocturnal ABL. The modeling results are compared with 24-h ABL evolution simulations by the third-order closure model and available in situ and laboratory measurements.
Atmospheric tides on Venus. III - The planetary boundary layer
NASA Technical Reports Server (NTRS)
Dobrovolskis, A. R.
Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.
Nonlinear Interaction of Frequency-Detuned Modes in Boundary Layers
NASA Technical Reports Server (NTRS)
Mankbadi, Reda R.
The present critical-layer asymptotic analysis for the nonlinear interaction of frequency-detuned modes in boundary-layer transition indicates that the interaction between a plane mode at the fundamental frequency and a pair of symmetrical oblique waves at the near-subharmonic frequency amplifies another pair of symmetrical oblique waves at the 'mirror frequency'. This type of interaction is stronger in the frequency-detuned case than the resonant triad case, and leads to a sharp drop in the oblique waves' peak with small detuning.
Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows
NASA Astrophysics Data System (ADS)
Yungster, Shaye
A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.
Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows
NASA Astrophysics Data System (ADS)
Yungster, Shaye
A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.
Flowfield analysis for successive oblique shock wave-turbulent boundary layer interactions
NASA Technical Reports Server (NTRS)
Sun, C. C.; Childs, M. E.
A computation procedure is described for predicting the flowfields which develop when successive interactions between oblique shock waves and a turbulent boundary layer occur. Such interactions may occur, for example, in engine inlets for supersonic aircraft. Computations are carried out for axisymmetric internal flows at M 3.82 and 2.82. The effect of boundary layer bleed is considered for the M 2.82 flow. A control volume analysis is used to predict changes in the flow field across the interactions. Two bleed flow models have been considered. A turbulent boundary layer program is used to compute changes in the boundary layer between the interactions. The results given are for flows with two shock wave interactions and for bleed at the second interaction site. In principle the method described may be extended to account for additional interactions. The predicted results are compared with measured results and are shown to be in good agreement when the bleed flow rate is low (on the order of 3% of the boundary layer mass flow), or when there is no bleed. As the bleed flow rate is increased, differences between the predicted and measured results become larger. Shortcomings of the bleed flow models at higher bleed flow rates are discussed.
Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows
NASA Technical Reports Server (NTRS)
Yungster, Shaye
A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.
A solution to Prandtl's boundary layer equations using direct, formal integration
NASA Astrophysics Data System (ADS)
Mokkapati, Ramakrishna
Direct, Formal Integration (DFI) is a new solution technique for differential equations. It is a simple method. The differential equation at hand is integrated formally with respect to any of the independent variables as many times as required. This results in an integral or an integro-differential equation. The resulting Volterra equation is then solved numerically using a simple quadrature formula such as the trapezoidal rule. To date DFI has been applied to numerous problems, mostly in the area of boundary layer flow, with very good results. Some details of its application to the linear heat equation are given. It was applied to the incompressible boundary layer with great success. The code generated was used to study the development of similarity profiles starting from non-similar initial conditions. It is also used to study the inverse boundary layer problem. Some results of these successful studies are included. The new method is implemented for the 2-D compressible boundary layer equations expressed in primitive variables. Numerical results are compared to those obtained from the Keller-Cebeci box method. DFI compares extremely well both in accuracy and in CPU time. Also, since the last major implementation of DFI, that is, to the incompressible boundary layer flow, numerous algorithmic enhancements were made. These are given in some detail.
Predicting Entropy Generation Rates in Transitional Boundary Layers Based on Intermittency
Kevin P. Nolan; Edmond J. Walsh; Donald M. McEligot; Ralph J. Volino
Prediction of thermodynamic loss in transitional boundary layers is typically based on time-averaged data only. This approach effectively ignores the intermittent nature of the transition region. In this work laminar and turbulent conditionally sampled boundary layer data for zero pressure gradient and accelerating transitional boundary layers have been analyzed to calculate the entropy generation rate in the transition region. By weighting the nondimensional dissipation coefficient for the laminar conditioned data and turbulent conditioned data with the intermittency factor, the entropy generation rate in the transition region can be determined and compared to the time-averaged data and correlations for laminar and turbulent flow. It is demonstrated that this method provides an accurate and detailed picture of the entropy generation rate during transition in contrast with simple time averaging. The data used in this paper have been taken from conditionally sampled boundary layer measurements available in the literature for favorable pressure gradient flows. Based on these measurements, a semi-empirical technique is developed to predict the entropy generation rate in a transitional boundary layer with promising results.
Acting Across Boundaries in Aboriginal Curriculum Development
Bolch, Tobias
Acting Across Boundaries in Aboriginal Curriculum Development: Examples from Northern British and for quotation purposes. Cross-roads in Aboriginal Curriculum Development: Examples from Northern British process. Collaborative curriculum development is, in this regard, much like other participatory
Possibilities for drag reduction by boundary layer control
NASA Technical Reports Server (NTRS)
Naiman, I.
The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.
Effects of surface wave breaking on the oceanic boundary layer
NASA Astrophysics Data System (ADS)
He, Hailun; Chen, Dake
Existing laboratory studies suggest that surface wave breaking may exert a significant impact on the formation and evolution of oceanic surface boundary layer, which plays an important role in the ocean-atmosphere coupled system. However, present climate models either neglect the effects of wave breaking or treat them implicitly through some crude parameterization. Here we use a one-dimensional ocean model (General Ocean Turbulence Model, GOTM) to investigate the effects of wave breaking on the oceanic boundary layer on diurnal to seasonal time scales. First a set of idealized experiments are carried out to demonstrate the basic physics and the necessity to include wave breaking. Then the model is applied to simulating observations at the northern North Sea and the Ocean Weather Station Papa, which shows that properly accounting for wave breaking effects can improve model performance and help it to successfully capture the observed upper ocean variability.
Additive erosion reduction influences in the turbulent boundary layer
NASA Astrophysics Data System (ADS)
Buckingham, A. C.
Results of a sequence of flow, heat and mass transfer calculations are presented which theoretically characterize the erosive environment at the wall surface of refractory metal coated and uncoated gun barrels. The theoretical results include analysis of the wall surface temperature, heat flux, and shear stress time histories on thin (10 mil.) Cr, Mo, Nb, and Ta plated steel barrel walls as uncoated steel walls. The calculations combine effects of a number of separate processes which were previously (and purposely) studied individually. These include solid particle additive concentrations, gas wall thermochemical influences, and transient turbulent wall boundary layer flow with multicomponent molecular diffusion and reactions from interaction of propellant combustion and the eroding surface. The boundary layer model includes particulate additive concentrations as well as propellant combustion products, considered for the present to be in the local thermochemical equilibrium.
A review of unsteady turbulent boundary-layer experiments
NASA Technical Reports Server (NTRS)
Carr, L. W.
The essential results of a comprehensive review of existing unsteady turbulent boundary-layer experiments are presented. Different types of unsteady flow facilities are described, and the related unsteady turbulent boundary-layer experiments are cataloged and discussed. The measurements that were obtained in the various experiments are described, and a complete list of experimental results is presented. All the experiments that measured instantaneous values of velocity, turbulence intensity, or turbulent shear stress are identified, and the availability of digital data is indicated. The results of the experiments are analyzed, and several significant trends are identified. An assessment of the available data is presented, delineating gaps in the existing data, and indicating where new or extended information is needed. Guidelines for future experiments are included.
Boundary layer integral matrix procedure code modifications and verifications
NASA Technical Reports Server (NTRS)
Evans, R. M.; Morse, H. L.
A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented.
Investigation of Turbulent Boundary-Layer Separation Using Laser Velocimetry
NASA Technical Reports Server (NTRS)
Modarress, D.; Johnson, D. A.
Boundary-layer measurements realized by laser velocimetry are presented for a Much 2.9, two-dimensional, shock-wave/turbulent boundary-layer interaction containing an extensive region of separated flow. Mean velocity and turbulent intensity profiles were obtained from upstream of the interaction zone to downstream of the mean reattachment point. The superiority of the laser velocimeter technique over pressure sensors in turbulent separated flows is demonstrated by a comparison of the laser velocimeter data with results obtained from local pilot and static pressure measurements for the same flow conditions. The locations of the mean separation and reattachment points as deduced from the mean velocity measurements are compared to oil-now visualization results. Representative velocity probability density functions obtained in the separated now region are also presented. Critical to the success of this investigation were: the use of Bragg cell frequency shifting and artificial seeding of the now with submicron light-scattering particles.
Turbulent heat flux measurements in a transitional boundary layer
NASA Technical Reports Server (NTRS)
Sohn, K. H.; Zaman, K. B. M. Q.; Reshotko, E.
During an experimental investigation of the transitional boundary layer over a heated flat plate, an unexpected result was encountered for the turbulent heat flux (bar-v't'). This quantity, representing the correlation between the fluctuating normal velocity and the temperature, was measured to be negative near the wall under certain conditions. The result was unexpected as it implied a counter-gradient heat transfer by the turbulent fluctuations. Possible reasons for this anomalous result were further investigated. The possible causes considered for this negative bar-v't' were: (1) plausible measurement error and peculiarity of the flow facility, (2) large probe size effect, (3) 'streaky structure' in the near wall boundary layer, and (4) contributions from other terms usually assumed negligible in the energy equation including the Reynolds heat flux in the streamwise direction (bar-u't'). Even though the energy balance has remained inconclusive, none of the items (1) to (3) appear to be contributing directly to the anomaly.
Atmospheric surface and boundary layers of the Amazon Basin
NASA Technical Reports Server (NTRS)
Garstang, Michael
Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.
On the instability of boundary layers on heated flat plates
NASA Technical Reports Server (NTRS)
Hall, Philip; Morris, Helen
The stability of a boundary layer on a heated flat plate is investigated in the linear regime. The flow is shown to be unstable to longitudinal vortex structures which in general develop in a nonparallel manner in the streamwise direction. Solutions of the nonparallel equations are obtained numerically at O(1) values of the appropriate stability parameter, i.e., the Grashof number. The particular cases investigated relate to the situations when the instability is induced by localized or distributed wall roughness or nonuniform wall heating. The case when the vortices are induced by freestream disturbances is also considered. The fastest growing mode is found to be governed by a quasi-parallel theory at high wavenumbers. The wavenumber and growth rate of the fastest growing mode are found in closed form. At low wavenumbers the vortex instability is shown to be closely related to Tollmein-Schlichting waves. The effect of wall heating or cooling on the latter type of instability is discussed.
Recommendations for Hypersonic Boundary Layer Transition Flight Testing
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Kimmel, Roger; Reshotko, Eli
Much has been learned about the physics underlying the transition process at supersonic and hypersonic speeds through years of analysis, experiment and computation. Generally, the application of this knowledge has been restricted to simple shapes like plates, cones and spherical bodies. However, flight reentry vehicles are in reality never simple. They typically are highly complex geometries flown at angle of attack so three-dimensional effects are very important, as are roughness effects due to surface features and/or ablation. This paper will review our present understanding of the physics of the transition process and look back at some of the recent flight test programs for their successes and failures. The goal of this paper is to develop rationale for new hypersonic boundary layer transition flight experiments. Motivations will be derived from both an inward look at what we believe constitutes a good flight test program as well as an outward review of the goals and objectives of some recent US based unclassified proposals and programs. As part of our recommendations, this paper will address the need for careful experimental work as per the guidelines enunciated years ago by the U.S. Transition Study Group. Following these guidelines is essential to obtaining reliable, usable data for allowing refinement of transition estimation techniques.
Partially exposed polymer dispersed liquid crystals for boundary layer investigations
NASA Technical Reports Server (NTRS)
Parmar, Devendra S.; Singh, Jag J.
A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.
Plasmoid observations in the distant plasma sheet boundary layer
Moldwin, M.B.; Hughes, W.J. (Boston Univ., MA (United States))
Substorm associated large amplitude bipolar magnetic events occurred when ISEE 3 was in the distant geotail's plasma sheet boundary layer (PSBL). The characteristics of these events, their substorm association and their possible source mechanisms are examined. We propose that these PSBL events are signatures of a passing plasmoid in the plasma sheet, analogous to the traveling compression region model in the geomagnetic lobes. 20 refs.
Prediction of boundary-layer characteristics of an oscillating airfoil
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
The evolution of unsteady boundary layers on oscillating airfoils is investigated by solving the governing equations by the Characteristic Box scheme. The difficulties associated with computing the first profile on a given time line, and the velocity profiles with partial flow reversal are solved. A sample calculation is performed for an external velocity distribution typical of those found near the leading edge of thin airfoils. The viability of the calculation procedure is demonstrated.
Performances of feature tracking in turbulent boundary layer investigation
M. Miozzi; B. Jacob; A. Olivieri
In this paper, we describe the application of a feature tracking (FT) algorithm for the measurement of velocity statistics\\u000a in a turbulent boundary layer over a flat plate at Re\\u000a ?�?�3,700. The feature tracking algorithm is based on an optical flow approach. Displacements are obtained by searching the\\u000a parameters of the mapping between interrogation windows in the first and second
The growth of Goertler vortices in compressible boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip; Malik, Mujeeb R.
The linear instability of Goertler vortices in compressible boundary layers is considered. Using asymptotic methods in the high wavenumber regime, it is shown that a growth rate estimate can be found by solving a sequence of linear equations. The growth rate obtained in this way takes non-parallel effects into account and can be found much more easily than by ordinary differential equation eigenvalue calculations associated with parallel flow theories.
The Turbulent Structure of Drag Reducing Boundary Layer Flows
C. M. White; V. Somandepalli; M. G. Mungal
The turbulent structure of wall-bounded drag reduced flow has been studied with particle image velocimetry (PIV) in a zero-pressure-gradient boundary layer. Drag reduction was achieved by injection of a concentrated polymer solution through a spanwise slot along the test wall at a distance approximately 2 m upstream of the PIV measurement station. For comparison, water was injected at the same