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Laminar Incompressible Flow Past Parabolic Bodies at Angles of Attack
Ercan Erturk; Thomas Corke; Osamah Haddad
Numerical solutions of a two-dimensional steady laminar incompressible flow over semi-infinite parabolic bodies at angles of attack are obtained. All solutions are found by using a modified numerical approach to solve the time-dependent Navier-Stokes equations. A check of our solutions to those that exist in the literature at zero angle of attack showed excellent agreement. In addition, at zero angle
Laminar Incompressible Flow Past Parabolic Bodies at Angles of Attack
Ercan Erturk; Thomas Corke; Osamah Haddad
Numerical solutions of a two-dimensional steady laminar incompressible flow over semi-infinite parabolic bodies at angles of attack are obtained. All solutions are found by using a modified numerical approach to solve the time- dependent Navier-Stokes equations. The governing equations are written for the stream function and vorticity variables and are solved on a nonuniform body-fitted parabolic grid. A check of
Transient radiative energy transfer in incompressible laminar flows
NASA Technical Reports Server (NTRS)
Tiwari, S. N.; Singh, D. J.
Analysis and numerical procedures are presented to investigate the transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these. Transient and steady-state results are obtained for the temperaure distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.
Numerical analysis of laminar and turbulent incompressible flows using the finite element Fluid Dynamics Analysis Package (FIDAP)
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.
The purpose of the study is the evaluation of the numerical accuracy of FIDAP (Fluid Dynamics Analysis Package). Accordingly, four test problems in laminar and turbulent incompressible flows are selected and the computational results of these problems compared with other numerical solutions and/or experimental data. These problems include: (1) 2-D laminar flow inside a wall-driven cavity; (2) 2-D laminar flow over a backward-facing step; (3) 2-D turbulent flow over a backward-facing step; and (4) 2-D turbulent flow through a turn-around duct.
Inertia effects on the dynamics of a disk levitated by incompressible laminar fluid flow
NASA Astrophysics Data System (ADS)
Warinner, D. K.; Pearson, J. T.
A nonlinear ordinary differential equation (ODE) of motion for a disk parallel to a flat plate and levitated by incompressible laminar flow of fluid supplied from a central orifice is developed. The fluid's inertia, reflected in high mass flow rates, is accounted for. The transient flow velocity and pressure field are found by iterative integration of the Navier-Stokes equation to determine the ODE for the time-dependent height of the disk (or fluid film thickness). The film thickness is found by not only numerically integrating the ODE, but also by linearizing the equation to obtain a closed-form solution. The results of this combined squeeze-film, source-flow case compare favorably with experimental data presented which span cases from negligible inertia (viscous dominance) to cases of inertia dominance. Fortunately, the closed-form solution differs only slightly from the numerical solution; this provides relatively accurate expressions for the frequencies and damping coefficients in terms of the geometry, load (or weight of disk), mass flow rate, and the fluid properties.
Computer-aided analysis of two-dimensional laminar and turbulent incompressible flows
NASA Astrophysics Data System (ADS)
Sheikholeslami, Mohamad Zahed
A new finite analytic (FA) numerical solution is obtained for the governing equations of two-dimensional incompressible laminar and turbulent flows. In obtaining the numerical solution the FA method is modified by introducing a new boundary function, a piecewise constant-exponential function for the finite analytic element. The finite analytic solutions obtained from this improved formulation is compared to other existing numerical solutions for some benchwork convection-diffusion equations. It is found that the FA method is a stable numerical method in that the new FA solution never exhibits over or under-shoot due to numerical approximation of the governing partial differential equations. In addition to the new boundary function, a new linearizing scheme for the convective term is proposed for solving the general convection-diffusion equation including the Navier-Stokes equations. This linearization scheme employs the idea of upwinding by selecting a point in the FA element whose velocity can best represent the convective velocity over the whole element. The FA method developed herein is used to predict several turbulent flows.
Conjugate Heat Transfer Study of Two-Dimensional Laminar Incompressible Offset Jet Flows
P. Rajesh Kanna; Manab Kumar Das
Steady-state conjugate heat transfer study of a slab and fluid is carried out for a two-dimensional laminar incompressible offset jet. The unsteady stream function¢vorticity formulation is used to solve the governing equations. The energy equation in the fluid and the conduction equation in the solid are solved simultaneously. The conjugate heat transfer characteristics are studied with four parameters, Re, Pr,
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.
Laminar and turbulent incompressible fluid flow analysis with heat transfer by the finite element method
Robert James Cochran
A study of the finite element method applied to two-dimensional incompressible fluid flow analysis with heat transfer is performed using a mixed Galerkin finite element method with the primitive variable form of the model equations. Four biquadratic, quadrilateral elements are compared in this study--the serendipity biquadratic element with bilinear continuous pressure interpolation (Q2(8)-Q1) and the Lagrangian biquadratic element with bilinear
Natural laminar flow and laminar flow control
NASA Technical Reports Server (NTRS)
Barnwell, R. W. (editor); Hussaini, M. Y. (editor)
The present volume discusses the development history and basic concepts of laminar flow control, laminar flow flight experiments, subsonic laminar-flow airfoils, and a design philosophy for long-range laminar flow-control commercial transports with advanced supercritical airfoils. Also discussed are the relationship of wave-interaction theory to laminar flow control, supersonic laminar flow control, and the NASA-Langley 8-ft Transonic Pressure Tunnel.
The pulsating viscous flow superposed on the steady laminar motion of incompressible fluid in a circular pipe
Shigeo Uchida
Summary An exact solution of pulsating laminar flow superposed on the steady motion in a circular pipe is presented under the assumption of parallel flow to the axis of pipe. Total mass of flow on time average is found to be identified with that given byHagen-Poiseuille's low calculated on the steady component of pressure gradient. The phase lag of velocity
Optimum plane diffusers in laminar flow
Hayri Cabuk; Vijay Modi
The paper considers an optimum design of an internal flow component such as a diffuser in laminar flow. The problem of determining the profile of a plane diffuser of given upstream width and length that provides the maximum static pressure rise is solved for 2D incompressible laminar flow governed by the steady-state Navier-Stokes equations. A set of 'adjoint' equations is
Laminar flow: The Cessna perspective
NASA Technical Reports Server (NTRS)
Peterman, Bruce E.
A review of Natural Laminar Flow (NLF) and Laminar-Flow Control activities over the last twenty years at the Cessna Aircraft Company is presented. Expected NLF benefits and remaining challenges are then described.
Vorticity and Incompressible Flow
Andrew J. Majda; Andrea L. Bertozzi
This book is a comprehensive introduction to the mathematical theory of vorticity and incompressible flow ranging from elementary introductory material to current research topics. Although the contents center on mathematical theory, many parts of the book showcase the interactions among rigorous mathematical theory, numerical, asymptotic, and qualitative simplified modeling, and physical phenomena. The first half forms an introductory graduate course
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, Ching F.
The objective of the research is to understand supersonic laminar flow stability, transition, and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of supersonic laminar flow with distributed heating and cooling on active control will be studied. The primary tasks of the research applying to the NASA/Ames Proof of Concept (POC) Supersonic Wind Tunnel and Laminar Flow Supersonic Wind Tunnel (LFSWT) nozzle design with laminar flow control are as follows: (1) predictions of supersonic laminar boundary layer stability and transition, (2) effects of wall heating and cooling for supersonic laminar flow control, and (3) performance evaluation of POC and LFSWT nozzles design with wall heating and cooling effects applying at different locations and various length.
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Fischer, M. C.
Laminar flow control is a technology with great potential for aircraft drag reduction. Stabilization of laminar boundary layers became known as natural laminar flow (NLF) and research led to the development of NLF airfoils. Research was also conducted on stabilization by suction, referred to as laminar flow control (LFC). Experiments demonstrated that extensive laminar flow could be achieved in flight. However, there remained doubts regarding the practicality of producing, with the technology then available, wing surfaces sufficiently smooth and wavefree to meet laminar-flow criteria and maintaining the wing surface quality in normal service. In 1976, the Aircraft Energy Efficiency (ACEE) program was begun by NASA to develop fuel-conservative technology for commercial transports. The progress of the ACEE program is discussed. Attention is given to LFC wing structures, and LFC leading-edge systems.
Development of a flow-condition-based interpolation 9-node element for incompressible flows
Banijamali, Bahareh
The Navier-Stokes equations are widely used for the analysis of incompressible laminar flows. If the Reynolds number is increased to certain values, oscillations appear in the finite element solution of the Navier-Stokes ...
Flight experiences with laminar flow
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.
A review of natural laminar flow (NLF) flight experiences over the period from the 1930's to the present has been given to provide information on the achievability and maintainability of NLF in typical airplane operating environments. Significant effects of loss of laminar flow on airplane performance have been observed for several airplanes, indicating the importance of providing information on these changes to laminar flow airplane operators. Significant changes in airplane stability and control and maximum lift were observed in flight experiments with the loss of laminar flow. However, these effects can be avoided by proper selection of airfoils. Conservative laminar flow airfoil designs should be employed which do not experience significant loss of lift (caused by flow separation) upon the loss of laminar flow. Mechanisms have been observed for the effects of insect accumulation, flight through clouds and precipitation, and propeller slipstreams on laminar flow behavior. Fixed transition testing, in addition to free transition testing, is recommended as a new standard procedure for airplanes with surfaces designed to support laminar flow.
Triangular spectral elements for incompressible fluid flow
NASA Technical Reports Server (NTRS)
Mavriplis, Catherine; Van Rosendale, John
We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility and are better conditioned and more accurate than quadrilateral elements when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied to the Poisson equation and are validated. The triangular discretizations are then applied to the incompressible Navier-Stokes equations, and a laminar channel flow solution is given. The new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.
Triangular spectral elements for incompressible fluid flow
NASA Technical Reports Server (NTRS)
Mavriplis, C.; Vanrosendale, John
We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility than quadrilateral elements and are better conditioned and more accurate when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied and validated on the Poisson equation. These discretizations are then applied to the incompressible Navier-Stokes equations and a laminar channel flow solution is given. These new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.
Overview of Laminar Flow Control
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.
The history of Laminar Flow Control (LFC) from the 1930s through the 1990s is reviewed and the current status of the technology is assessed. Early studies related to the natural laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. Although most of this publication is about slot-, porous-, and perforated-suction LFC concept studies in wind tunnel and flight experiments, some mention is made of thermal LFC. Theoretical and computational tools to describe the LFC aerodynamics are included for completeness.
The stability of the flow in a laminar separation bubble
Tai Ran Niew
This dissertation reports a study into the underlying concepts used to analyze incompressible laminar separation bubbles. The suggestion that absolute instability could play a role in bubble flows was further developed, and was the focal point of this project. From a review of previous work and preliminary experiments on a backward faxing step, it was suggested that for some bubbles
Improved Algorithm Computes Incompressible Flow
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.
Algorithm numerically integrates Navier-Stokes equations of time-dependent or steady flow of incompressible, viscous fluid. Simulates realistic three-dimensional flows bounded by stationary or moving surface(s) of complicated shape(s). Only two arbitrary parameters specified by user. Algorithm described in "Numerical Simulation Of Flow Through An Artificial Heart" (ARC-12478). Algorithm tested by application to number of steady and unsteady flows, including flow in artificial heart discussed in noted prior article.
Laminar flow control is maturing
NASA Technical Reports Server (NTRS)
Wagner, Richard D.; Bartlett, Dennis W.; Maddalon, Dal V.
Recent research demonstrates that laminar flow (LF) can be reliable in flight and that the support system need not be complex. Shaping produces favorable pressure gradients for maintaining natural laminar flow (NLF), and laminar flow control (LFC) techniques such as full chord suction promise a fuel-saving payoff of up to 30 percent on long-range missions. For large aircraft, current research is concentrated on hybrid LFC concepts which combine suction and pressure-gradient control. At NASA Ames, an F-14 with variable wing sweep has been flight tested with smooth surface gloves on the wings; preliminary results indicate high transition Reynolds numbers to sweep angles as large as 25 deg. In addition, a 757 was flight tested with an NLF glove on the right wing just outboard of the engine pylon; and the LF was found to be suprisingly robust.
McDonough, James M.
LECTURES in COMPUTATIONAL FLUID DYNAMICS of INCOMPRESSIBLE FLOW: Mathematics, Algorithms 1991, 2003, 2007 #12;PROLOGUE Computational fluid dynamics (CFD) can be traced to the early attempts at the beginning of the Cold War. In fact, such efforts were prime drivers in the development of digital computers
Laminar-flow flight experiments
NASA Technical Reports Server (NTRS)
Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.
The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time.
Radiative interactions in laminar duct flows
NASA Technical Reports Server (NTRS)
Trivedi, P. A.; Tiwari, S. N.
Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows.
Operational considerations for laminar flow aircraft
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Wagner, Richard D.
Considerable progress has been made in the development of laminar flow technology for commercial transports during the NASA Aircraft Energy Efficiency (ACEE) laminar flow program. Practical, operational laminar flow control (LFC) systems have been designed, fabricated, and are undergoing flight testing. New materials, fabrication methods, analysis techniques, and design concepts were developed and show much promise. The laminar flow control systems now being flight tested on the NASA Jetstar aircraft are complemented by natural laminar flow flight tests to be accomplished with the F-14 variable-sweep transition flight experiment. An overview of some operational aspects of this exciting program is given.
Laminar flow research applicable to subsonic aircraft
NASA Technical Reports Server (NTRS)
Hefner, J. N.; Wagner, R. D.
Since the beginning of the NASA Aircraft Energy Efficiency (ACEE) program in 1976, significant progress has been made in the development of laminar flow technology for general aviation, commuter, and transport aircraft. Exploitation of new materials, fabrication methods, analysis techniques, and design concepts is providing convincing evidence that practical laminar flow control (LFC) systems for these future subsonic aircraft could become a reality. Program studies indicate that extensive laminar flow might be achieved on small transports with natural laminar flow (NLF) wings and larger transports with hybrid laminar flow (i.e., leading-edge suction on an NLF type of wing). This paper presents an overview of these laminar flow technology developments and describes future efforts in a broadened NASA program to explore the potential and to evaluate the practicality of different laminar flow concepts for commercial transports.
Spiral Laminar Flow: A revolution in understanding?
Greenaway, Alan
Blood Flow Spiral laminar flow #12;Spiral flow in the Aorta (MRI) Computational Fluid Dynamics 0 10 20Spiral Laminar Flow: A revolution in understanding? Reintroduction of natural blood flow - Amputation #12;Understanding Arterial Disease Arterial Blood Flow #12;Understanding Arterial Disease Arterial
Meinhard T. Schobeiri
\\u000a As briefly discussed in Chapter 4, the motion of Newtonian fluids is described by the Navier-Stokes equations. Due to the\\u000a non-linear nature of these equations and the general complexity of the flow geometry, analytical solutions of Navier-StokeÆs\\u000a equations has been exhibiting a major problem in fluid mechanics. The continuous development in the area of computer technology\\u000a and the introduction of
Laminar and Turbulent Flow in Water
ERIC Educational Resources Information Center
Riveros, H. G.; Riveros-Rosas, D.
There are many ways to visualize flow, either for laminar or turbulent flows. A very convincing way to show laminar and turbulent flows is by the perturbations on the surface of a beam of water coming out of a cylindrical tube. Photographs, taken with a flash, show the nature of the flow of water in pipes. They clearly show the difference betweenģ
Computational Challenges of Viscous Incompressible Flows
NASA Technical Reports Server (NTRS)
Kwak, Dochan; Kiris, Cetin; Kim, Chang Sung
Over the past thirty years, numerical methods and simulation tools for incompressible flows have been advanced as a subset of the computational fluid dynamics (CFD) discipline. Although incompressible flows are encountered in many areas of engineering, simulation of compressible flow has been the major driver for developing computational algorithms and tools. This is probably due to the rather stringent requirements for predicting aerodynamic performance characteristics of flight vehicles, while flow devices involving low-speed or incompressible flow could be reasonably well designed without resorting to accurate numerical simulations. As flow devices are required to be more sophisticated and highly efficient CFD took become increasingly important in fluid engineering for incompressible and low-speed flow. This paper reviews some of the successes made possible by advances in computational technologies during the same period, and discusses some of the current challenges faced in computing incompressible flows.
Applied aspects of laminar-flow technology
NASA Technical Reports Server (NTRS)
Braslow, A. L.; Maddalon, D. V.; Bartlett, D. W.; Wagner, R. D.; Collier, F. S., Jr.
An account is given of the development status and performance levels achieved with natural laminar flow (NLF), extended wing chord laminar flow control (LFC), and hybrid laminar flow control (HLFC) concepts combining NLF and partial-chord LFC in the leading-edge region. Attention is given to NLF wing structure construction methods capable of achieving the requisite surface-irregularity tolerances, LFC through wing surface suction slots or perforated skins, and the deleterious effects of insects, ice crystals, and noise disturbance inputs on the ability of NLF, LFC, and HLFC wings to maintain effective laminar flow operation.
Laminar boundary layer swirling flow with heat and mass transfer in conical nozzles and diffusers
B. K. Meena; G. Nath
The flow and heat transfer for a steady axisymmetric laminar incompressible boundary layer swirling flow with mass transfer in a conical nozzle and a diffuser have been studied. The partial differential equations governing nonsimilar flow have been solved numerically using an implicit finite-difference scheme after transforming them into new coordinates having finite ranges. The results indicate that, both for the
Laminar-flow wind tunnel experiments
NASA Technical Reports Server (NTRS)
Harvey, William D.; Harris, Charles D.; Sewall, William G.; Stack, John P.
Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.
Faster Algorithm For Computation Of Incompressible Flow
NASA Technical Reports Server (NTRS)
Rogers, S. E.; Kwak, D.; Kiris, C.
Improved algorithm yields faster numerical solutions of Navier-Stokes equations of steady or unsteady three-dimensional flow of incompressible fluid. In artificial-compressibility method, unsteady flow treated as incompressible in advancing from one time step to next, but at each time step (or in steady state), fluid treated as having variable compressibility enabling propagation of flow field, and subiterations performed in increments of pseudotime until effects of compressibility subside. Directly couples pressure and velocity fields at same time step and converts elliptic incompressible Navier-Stokes equations to hyperbolic form more amenable to numerical integration.
Natural laminar flow application to transport aircraft
NASA Technical Reports Server (NTRS)
Gratzer, Louis B.
A major goal of NASA during the last 15 years has been the development of laminar flow technology for aircraft drag reduction. Of equal importance is achieving a state of readiness that will allow the successful application of this technology by industry to large, long-range aircraft. Recent progress in achieving extensive laminar flow with limited suction on the Boeing 757 has raised the prospects from practical application of the hybrid laminar flow control (HLFC) concept to subsonic aircraft. Also, better understanding of phenomena affecting laminar flow stability and response to disturbances has encouraged consideration of natural laminar flow (NLF), obtained without suction or active mechanical means, for application to transport aircraft larger than previously thought feasible. These ideas have inspired the current NASA/ASEE project with goals as follows: explore the feasibility of extensive NLF for aircraft at high Reynolds number under realistic flight conditions; determine the potential applications of NLF technology and the conditions under which they may be achieved; and identify existing aircraft that could be adapted to carry out flight experiments to validate NLF technology application. To achieve these objectives, understanding of the physical limits to natural laminar flow and possible ways to extend these limits was sought. The primary factors involved are unit Reynolds number, Mach number, wing sweep, thickness, and lift coefficients as well as surface pressure gradients and curvature. Based on previous and ongoing studies using laminar boundary layer stability theory, the interplay of the above factors and the corresponding transition limits were postulated.
Fifty years of laminar flow flight testing
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Maddalon, D. V.; Bartlett, D. W.; Collier, F. S., Jr.
Laminar flow flight experiments conducted over the past 50 years are reviewed. The emphasis is on flight testing conducted under the NASA Laminar Flow Control Program, which has been directed towards the most challenging technology application, the high-subsonic-speed transport. The F111/TACT NLF Glove Flight Test, the F-14 Variable-Sweep Transition Flight Experiment, the 757 Wing-Noise Survey and NLF Glove Flight Test, the NASA Jetstar Leading-Edge Flight Test Program, and the recently initiated Hybrid Laminar-Flow-Control Flight Experiment are discussed.
Heat Transfer Study of Two-Dimensional Laminar Incompressible Wall Jet over Backward-Facing Step
P. Rajesh Kanna; Manab Kumar Das
A steady-state heat transfer study is carried out for a two-dimensional, laminar, incompressible, plane wall jet over a backward-facing step. An unsteady stream function¢vorticity formulation is used to solve the governing equations. The heat transfer characteristics of the jet as functions of Reynolds number (Re), Prandtl number (Pr), and step geometry (step length l and step height s) are reported
Laminar Flow Control Flight Experiment DesignĀ
Tucker, Aaron 1975-
this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE...
A faster 'transition' to laminar flow
NASA Technical Reports Server (NTRS)
Bobbitt, P. J.; Waggoner, E. G.; Harvey, W. D.; Dagenhart, J. R.
A discussion is given of the ongoing research related to laminar flow airfoils, nacelles, and wings where the laminar flow is maintained by a favorable pressure gradient, surface suction or a combination of the two. Design methologies for natural laminar flow airfoil sections and wings for both low and high speed applications are outlined. Tests of a 7-foot chord, 23-deg sweep laminar flow-control airfoil at high subsonic Mach numbers are described, along with the associated stability theory used to design the suction system. The state-of-the-art of stability theory is simply stated and a typical calculation illustrated. In addition, recent computer simulations of transition using the time dependent Navier-Stokes equations are briefly described. Advances in wind tunnel capabilities and instrumentation will be reviewed, followed by the presentation of a few results from both wind tunnels and flight. Finally, some suggestions for future work will complete the paper.
Research in natural laminar flow and laminar-flow control, part 3
Hefner, J.N.; Sabo, F.E.
Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic/hypersonic wind tunnels; and boundary layer instability mechanisms on swept leading edges at supersonic speeds.
Research in natural laminar flow and laminar-flow control, part 3
J. N. Hefner; F. E. Sabo
Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition\\/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic\\/hypersonic wind tunnels; and boundary layer instability mechanisms on
Research in Natural Laminar Flow and Laminar-Flow Control, part 3
NASA Technical Reports Server (NTRS)
Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)
Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic/hypersonic wind tunnels; and boundary layer instability mechanisms on swept leading edges at supersonic speeds.
Accurate 3D viscous incompressible flow calculations with the FEM
NASA Astrophysics Data System (ADS)
G³at, ▄.; Aslan, A. R.
A second-order-accurate (in both time and space) formulation is developed and implemented for solution of the three-dimensional incompressible Navier-Stokes equations involving high-Reynolds-number flows past complex configurations. For stabilization, only a fourth-order-accurate artificial dissipation term in the momentum equations is used. The finite element method (FEM) with an explicit time-marching scheme based on two-fractional-step integration is used for solution of the momentum equations. The element-by-element (EBE) technique is employed for solution of the auxiliary potential function equation in order to ease the memory requirements for matrix. The cubic cavity problem, the laminar flow past a sphere at various Reynolds numbers and the flow around the fuselage of a helicopter are successfully solved. Comparison of the results with the low-order solutions indicates that the flow details are depicted clearly even with coarse grids.
Efficient solutions of two-dimensional incompressible steady viscous flows
NASA Technical Reports Server (NTRS)
Morrison, J. H.; Napolitano, M.
A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.
A computational model for three-dimensional incompressible wall jets with large cross flow
NASA Technical Reports Server (NTRS)
Murphy, W. D.; Shankar, V.; Malmuth, N. D.
A computational model for the flow field of three dimensional incompressible wall jets prototypic of thrust augmenting ejectors with large cross flow is presented. The formulation employs boundary layer equations in an orthogonal curvilinear coordinate system. Simulation of laminar as well as turbulen wall jets is reported. Quantification of jet spreading, jet growth, nominal separation, and jet shrink effects due to corss flow are discussed.
Cylindrical ideal magnetohydrodynamic equilibria with incompressible flows
Throumoulopoulos, G.N. [Section of Theoretical Physics, Department of Physics, University of Ioannina, GR 451 10 Ioannina (Greece)] [Section of Theoretical Physics, Department of Physics, University of Ioannina, GR 451 10 Ioannina (Greece); Tasso, H. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)] [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)
It is proved that (a) the solutions of the ideal magnetohydrodynamic equation, which describes the equilibrium states of a cylindrical plasma with purely poloidal flow and arbitrary cross-sectional shape [G. N. Throumoulopoulos and G. Pantis, Plasma Phys. Controlled Fusion {bold 38}, 1817 (1996)], are also valid for incompressible equilibrium flows with the axial velocity component being a free surface quantity and that (b) for the case of isothermal incompressible equilibria the magnetic surfaces necessarily have a circular cross-section. {copyright} {ital 1997 American Institute of Physics.}
Finite element computation of incompressible flows
NASA Technical Reports Server (NTRS)
Tezduyar, T. E.; Mittal, S.
Among the solution techniques presented for FEM computation of incompressible flows are stabilized formulations designed to prevent the numerical oscillations that may be generated by (1) the presence of dominant advection terms in the governing equations, or (2) the failure to use an acceptable combination of interpolation functions to represent velocity and pressure fields. It is shown that the space-time formulation, in conjunction with the Galerkin-least squares methods, can be used to compute steady incompressible flows involving moving boundaries and interfaces; it is recommended that iteration methods be used to reduce the associated computational costs.
Velocity-split Navier-Stokes solution procedure for incompressible high Reynolds number external flows
NASA Technical Reports Server (NTRS)
Dwoyer, D. L.
A method for solving the Navier-Stokes equations based on splitting the velocity vector into its rotational and irrotational parts was sucessfully applied to internal flow computations. The applicability of the method to external flows is examined by studying several model problems. The model problems are those of laminar and turbulent incompressible flow past a semi-infinite flat plate and laminar incompressible flow past a finite flat plate. For these problems, the procedure accurately reproduces the known solutions and is computationally very efficient even at high Reynolds numbers. Computational aspects of the method are discussed along with the possibility of using the procedure to retrofit a viscous capability into existing potential flow codes.
Laminar flow - The past, present, and prospects
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Bartlett, D. W.; Collier, F. S., Jr.
Flight research conducted on natural laminar flow (NLF) is discussed. Emphasis is on recent flight testing conducted by the National Aeronautics and Space Administration. To place these flight experiences in perspective, important flight tests from the early days of natural laminar flow research are first reviewed to recall the lessons learned at that time. Then, based on more recent flight experiences and analyses with state-of-the-art boundary layer stability theory, speculation is made on the possibility of extensive NLF on swept wing transport aircraft.
Boundary conditions for incompressible flows
NASA Astrophysics Data System (ADS)
Orszag, Steven A.; Israeli, Moshe; Deville, Michel O.
A general framework is presented for the formulation and analysis of rigid no-slip boundary conditions for numerical schemes for the solution of the incompressible Navier-Stokes equations. It is shown that fractional-step (splitting) methods are prone to introduce a spurious numerical boundary layer that induces substantial time differencing errors. High-order extrapolation methods are analyzed to reduce these errors. Both improved pressure boundary condition and velocity boundary condition methods are developed that allow accurate implementation of rigid no-slip boundary conditions.
Unsteady incompressible flow computations with quadrilateral elements
NASA Technical Reports Server (NTRS)
Tezduyar, T. E.; Shih, R.; Mittal, S.
A comparative investigation, based on a series of numerical tests, of various velocity-pressure elements used for incompressible flow computations is presented. These elements are implemented in conjunction with one-step and multi-step temporal integration of unsteady Navier-Stokes equations. The test cases chosen are the standing vortex problem, the lid-driven cavity flow, and flow past a circular cylinder.
Aerodynamic Design for Swept-wing Laminar Flow
Belisle, Michael Joseph
(SARGE), a natural laminar flow and passive laminar flow control wing glove flight experiment funded by the NASA Environmentally Responsible Aviation initiative. The experiment seeks to raise the technology readiness level of the spanwise...
CFD analysis of laminar oscillating flows
Booten, C. W. Charles W.); Konecni, S. (Snezana); Smith, B. L. (Barton L.); Martin, R. A. (Richard A.)
This paper describes a numerical simulations of oscillating flow in a constricted duct and compares the results with experimental and theoretical data. The numerical simulations were performed using the computational fluid dynamics (CFD) code CFX4.2. The numerical model simulates an experimental oscillating flow facility that was designed to test the properties and characteristics of oscillating flow in tapered ducts, also known as jet pumps. Jet pumps are useful devices in thermoacoustic machinery because they produce a secondary pressure that can counteract an unwanted effect called streaming, and significantly enhance engine efficiency. The simulations revealed that CFX could accurately model velocity, shear stress and pressure variations in laminar oscillating flow. The numerical results were compared to experimental data and theoretical predictions with varying success. The least accurate numerical results were obtained when laminar flow approached transition to turbulent flow.
Algebraic Flux Correction III. Incompressible Flow Problems
Kuzmin, Dmitri
a perfect starting point for the development of reliable numerical algorithms and efficient software for CFD-Stokes equations. The need for development of robust and efficient iterative solvers (outer Newton-like schemes of Computational Fluid Dynamics (CFD). Incompressible flow problems are especially interesting from the viewpoint
Direct numerical simulation of incompressible turbulent flows
R Friedrich; T. J H³ttl; M Manhart; C Wagner
The paper discusses recent achievements of direct numerical simulation (DNS) of incompressible flows. The various spatial discretization techniques which can be used in the case of simple or complex geometry are referred to, along with suitable time advancement schemes. The advantage of using a staggered variable arrangement and efficient Poisson solvers is stressed before initial and boundary conditions for inflow,
Working towards the ideal laminar flow structure
Bryan E. Humphreys
Airlines and aircraft manufacturers are forecasting significant incerases in passenger traffic over the next 20 years (1), (2) but it is becoming increasingly apparent that, given a future scenario of increasing fuel costs and environmental controls, this is unlikely to be sustainable unless aircraft become more efficient and environmentally friendly than those in service today.Hybrid Laminar Flow (HLF) offers a
Progress in natural laminar flow research
B. J. Holmes
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect
Flight research on natural laminar flow
B. J. Holmes; C. C. Croom; E. C. Hastings Jr.; C. J. Obara; C. P. Vandam
Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on
Laminar compressible flow in a tube
Robert K. Prud'Homme; Thomas W. Chapman; J. Ray Bowen
A two-dimensional solution for the velocity and pressure distributions in steady, laminar, isothermal flow of an ideal gas\\u000a in a long tube is obtained as a double perturbation expension in ?, the radius to length ratio, and ?, the relative pressure drop. It is found that simple approximations estimate the exact\\u000a flow rate-pressure drop relationship accurately.
Feasibility study of laminar flow bodies in fully turbulent flow
Sarkar, T.; Sayer, P.G.; Fraser, S.M. [Univ. of Strathclyde, Glasgow (United Kingdom)
One of the most important design requirements of long range autonomous underwater vehicles (AUVs) is to minimize propulsive power. An important and relatively easy way of achieving this is by careful selection of hull shape. Two main schools of thought in this respect are: if laminar flow can be maintained for a long length of the body, the effective drag can be reduced; it is not possible to maintain laminar flow for a significant length of the body and hull design should be based on turbulent flow conditions. In this paper, a feasibility study of laminar flow designs is undertaken under the assumption that flow will be turbulent over the entire length. For comparison two laminar flow designs X-35 and F-57 are selected and results are compared with those of two typical torpedo shaped bodies, namely AFTERBODY1 and AFTERBODY2 of DTNSRDC. It has been shown that laminar flow bodies have 10--15% higher drag when flow is turbulent over the entire length. Hence there is some hydrodynamic risk involved in adopting such laminar bodies without further consideration.
Investigation of a Laminar Flow Leading Edge
NASA Technical Reports Server (NTRS)
Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.; Zuniga, Fanny
The recent resurgence of interest in utilizing laminar flow on aircraft surfaces for reduction in skin friction drag has generated a considerable amount of research in natural laminar flow (NLF) and hybrid laminar flow control (HLFC) on transonic aircraft wings. This research has focused primarily on airfoil design and understanding transition behavior with little concern for the surface imperfections and manufacturing variations inherent to most production aircraft. In order for laminar flow to find wide-spread use on production aircraft, techniques for constructing the wings must be found such that the large surface imperfections present in the leading edge region of current aircraft do not occur. Toward this end, a modification to existing leading edge construction techniques was devised such that the resulting surface did not contain large gaps and steps as are common on current production aircraft of this class. A lowspeed experiment was first conducted on a simulation of the surface that would result from this construction technique. Preston tube measurements of the boundary layer downstream of the simulated joint and flow visualization using sublimation chemicals validated the literature on the effects of steps on a laminar boundary layer. These results also indicated that the construction technique was indeed compatible with laminar flow. In order to fully validate the compatibility of this construction technique with laminar flow, thus proving that it is possible to build wings that are smooth enough to be used on business jets and light transports in a manner compatible with laminar flow, a flight experiment is being conducted. In this experiment Mach number and Reynolds number will be matched in a real flight environment. The experiment is being conducted using the NASA Dryden F-104 Flight Test Fixture (FTF). The FTF is a low aspect ratio ventral fin mounted beneath an F-104G research aircraft. A new nose shape was designed and constructed for this experiment. This nose shape provides an accelerating pressure gradient in the leading edge region. By flying the aircraft at appropriate Mach numbers and altitudes, this nose shape simulates the leading edge region of a laminar flow wing for a business jet or light transport. Manufactured into the nose shape is a spanwise slot located approximately four inches downstream of the leading edge. The slot, which is an inch wide and one-eighth of an inch deep allows the simulation of surface imperfections, such as gaps and steps at skin joints, which will occur on aircraft using this new construction technique. By placing strips of aluminum of various sizes and shapes in the slot, the effect on the boundary layer of different sizes and shapes of steps and gaps will be examined. It is planned to use five different configurations, differing primarily in the size and number of gaps. Downstream of the slot, the state of the boundary layer is determined using hot film gages and Stanton gages. Agreement between these two very different techniques of measuring boundary layer properties is considered important to being able to state with confidence the effects on the boundary layer of the simulated manufacturing imperfections. To date, the aircraft has not flown. First flights of the aircraft are on schedule to begin October 4, 1993. Low-speed, preliminary experiments at matching Reynolds numbers have been completed.
Laminar flow instability in nuclear rockets
Black, D.L. (628 C Street, S. E., Washington, DC 20003-4302 (United States))
Laminar flow instability (LFI) is a rarely encountered phenomenon, occurring in gaseous heated channels with high exit-to-inlet temperature ratios and a laminar Reynolds Number at the channel exit, as may be experienced in a nuclear rocket. Analytical techniques were developed and programmed for parametric evaluation that had been previously validated by comparison with available experimental data. The four types of transients associated with LFI are described in terms of the governing equations. Parametric evaluations of solid core prismatic and particle bed fuel configurations were made to determine their sensitivities to LFI from temperature ratio, flow rate, orificing, transition Reynolds Number, pressure level, presence of an exit sonic nozzle, power density and heat flux shape. The flow rate at the point of neutral stability and the growth rate of the excursive transient are calculated. The full power design point and the cooldown phases of operation were both evaluated.
Smoothed Two-Dimensional Edges for Laminar Flow
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Liu, C. H.; Martin, G. L.; Domack, C. S.; Obara, C. J.; Hassan, A.; Gunzburger, M. D.; Nicolaides, R. A.
New concept allows passive method for installing flaps, slats, iceprotection equipment, and other leading-edge devices on natural-laminar-flow (NLF) wings without causing loss of laminar flow. Two-dimensional roughness elements in laminar boundary layers strategically shaped to increase critical (allowable) height of roughness. Facilitates installation of leading-edge devices by practical manufacturing methods.
Efficient solution of turbulent incompressible separated flows
Vittorio Michelassi; Francesco Martelli
A computational method for incompressible separated flows based on two-dimensional approximate factorization is presented. Turbulence effects are accounted for by low-Reynolds number forms of the k-epsilon model. Mass conservation is enforced by the artificial compressibility method. Decoupling and coupling of the equations of motions with the turbulence model equations are investigated. Testing of the coupled solver showed no improvement in
Natural laminar flow hits smoother air
NASA Technical Reports Server (NTRS)
Holmes, B. J.
Natural laminar flow (NLF) may be attained in aircraft with lower cost, weight, and maintenance penalties than active flow laminarization by means of a slot suction system. A high performance general aviation jet aircraft possessing a moderate degree of NLF over wing, fuselage, empennage and engine nacelles will accrue a 24 percent reduction in total aircraft drag in the cruise regime. NASA-Langley has conducted NLF research centered on the use of novel airfoil profiles as well as composite and milled aluminum alloy construction methods which minimize three-dimensional aerodynamic surface roughness and waviness. It is noted that higher flight altitudes intrinsically reduce unit Reynolds numbers, thereby minimizing turbulence for a given cruise speed.
Flight research on natural laminar flow
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Croom, C. C.; Hastings, E. C., Jr.; Obara, C. J.; Vandam, C. P.
Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on Lear 28/29; OV-I NLF engine nacelle experiments; and viscous drag reduction are examined.
Flight research on natural laminar flow
NASA Astrophysics Data System (ADS)
Holmes, B. J.; Croom, C. C.; Hastings, E. C., Jr.; Obara, C. J.; Vandam, C. P.
Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on Lear 28/29; OV-I NLF engine nacelle experiments; and viscous drag reduction are examined.
Laminar nanofluid flow in microheat-sinks
J. Koo; C. Kleinstreuer
In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nanospheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for microheat-sinks has been numerically solved. Employing new models for the effective thermal
Flow Solver for Incompressible Rectangular Domains
NASA Technical Reports Server (NTRS)
Kalb, Virginia L.
This is an extension of the Flow Solver for Incompressible 2-D Drive Cavity software described in the preceding article. It solves the Navier-Stokes equations for incompressible flow using finite differencing on a uniform, staggered grid. There is a runtime choice of either central differencing or modified upwinding for the convective term. The domain must be rectangular, but may have a rectangular walled region within it. Currently, the position of the interior region and exterior boundary conditions are changed by modifying parameters in the code and recompiling. These features make it possible to solve a variety of classical fluid flow problems such as an L-shaped cavity, channel flow, or wake flow past a square cylinder. The code uses fourth-order Runge-Kutta time-stepping and overall second-order spatial accuracy. This software permits the walled region to be positioned such that flow past a square cylinder, an L-shaped cavity, and the flow over a back-facing step can all be solved by reconfiguration. Also, this extension has an automatic detection of periodicity, as well as use of specialized data structure for ease of configuring domain decomposition and computing convergence in overlap regions.
Incompressible flow over delta wings
Nathman, James Kirwin
and modeled the primary vortex sheets as two point vortices lying above the wing. The position and strength of these vortices were determined by requiring no force on each vortex and a smooth flow off the leading edge. Brown and Michael expanded Legendre... and Experimental Results 32 also contribute to the slight discrepancy between the two curves since it puts a depression on the outboard side of the suction peak. The value of the fixed-wake model lies in its simplicity. The required input can be fitted on one...
Reducing numerical diffusion for incompressible flow calculations
NASA Technical Reports Server (NTRS)
Claus, R. W.; Neely, G. M.; Syed, S. A.
A number of approaches for improving the accuracy of incompressible, steady-state flow calculations are examined. Two improved differencing schemes, Quadratic Upstream Interpolation for Convective Kinematics (QUICK) and Skew-Upwind Differencing (SUD), are applied to the convective terms in the Navier-Stokes equations and compared with results obtained using hybrid differencing. In a number of test calculations, it is illustrated that no single scheme exhibits superior performance for all flow situations. However, both SUD and QUICK are shown to be generally more accurate than hybrid differencing.
Research in Natural Laminar Flow and Laminar-Flow Control, part 2
NASA Technical Reports Server (NTRS)
Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)
Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction.
Distributed apertures in laminar flow laser turrets
NASA Astrophysics Data System (ADS)
Tousley, B. B.
Assume a technology that permits undistorted laser beam propagation from the aft section of a streamlined turret. A comparison of power on a distant airborne target is made between a single aperture in a large scale streamlined turret with a turbulent boundary layer and various arrays of apertures in small scale streamlined turrets with laminar flow. The array performance is mainly limited by the size of each aperture. From an array one might expect, at best, about 40 percent as much power on the target as from a single aperture with equal area. Since the turbulent boundary layer on the large single-turret has negligible effect on beam quality, the array would be preferred (if all development efforts were essentially equal) only if a laminar wake is an operational requirement.
Subsonic natural-laminar-flow airfoils
NASA Technical Reports Server (NTRS)
Somers, Dan M.
An account is given of the development history of natural laminar-flow (NLF) airfoil profiles under guidance of an experimentally well-verified theoretical method for the design of airfoils suited to virtually all subcritical applications. This method, the Eppler Airfoil Design and Analysis Program, contains a conformal-mapping method for airfoils having prescribed velocity-distribution characteristics, as well as a panel method for the analysis of potential flow about given airfoils and a boundary-layer method. Several of the NLF airfoils thus obtained are discussed.
Skin-Friction Measurements in Incompressible Flow
NASA Technical Reports Server (NTRS)
Smith, Donald W.; Walker, John H.
Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.
Multigrid Approach to Incompressible Viscous Cavity Flows
NASA Technical Reports Server (NTRS)
Wood, William A.
Two-dimensional incompressible viscous driven-cavity flows are computed for Reynolds numbers on the range 100-20,000 using a loosely coupled, implicit, second-order centrally-different scheme. Mesh sequencing and three-level V-cycle multigrid error smoothing are incorporated into the symmetric Gauss-Seidel time-integration algorithm. Parametrics on the numerical parameters are performed, achieving reductions in solution times by more than 60 percent with the full multigrid approach. Details of the circulation patterns are investigated in cavities of 2-to-1, 1-to-1, and 1-to-2 depth to width ratios.
Simulation Of Unsteady, Viscous, Incompressible Flow
NASA Technical Reports Server (NTRS)
Rosenfeld, Moshe; Kwak, Dochan
Method for numerical solution of Navier-Stokes equations of viscous, incompressible flow developed based on use of fractional-step procedure. Accurate to second order in both space and time. Attempt made to minimize Poisson-equation difficulties by choosing pressures at centers and volume fluxes across faces of computational cells as dependent variables instead of familiar Cartesian components of velocity. Choice ensures satisfaction of discrete equation of conservation of mass to within round-off errors in any coordinate system and has favorable effects on convergence properties.
Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames
NASA Technical Reports Server (NTRS)
Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.
This is the final report of a research program considering interactions between flow and soot properties within laminar diffusion flames. Laminar diffusion flames were considered because they provide model flame systems that are far more tractable for theoretical and experimental studies than more practical turbulent diffusion flames. In particular, understanding the transport and chemical reaction processes of laminar flames is a necessary precursor to understanding these processes in practical turbulent flames and many aspects of laminar diffusion flames have direct relevance to turbulent diffusion flames through application of the widely recognized laminar flamelet concept of turbulent diffusion flames. The investigation was divided into three phases, considering the shapes of nonbuoyant round laminar jet diffusion flames in still air, the shapes of nonbuoyant round laminar jet diffusion flames in coflowing air, and the hydrodynamic suppression of soot formation in laminar diffusion flames.
Adjoint operator approach to shape design for internal incompressible flows
NASA Technical Reports Server (NTRS)
Cabuk, H.; Sung, C.-H.; Modi, V.
The problem of determining the profile of a channel or duct that provides the maximum static pressure rise is solved. Incompressible, laminar flow governed by the steady state Navier-Stokes equations is assumed. Recent advances in computational resources and algorithms have made it possible to solve the direct problem of determining such a flow through a body of known geometry. It is possible to obtain a set of adjoint equations, the solution to which permits the calculation of the direction and relative magnitude of change in the diffuser profile that leads to a higher pressure rise. The solution to the adjoint problem can be shown to represent an artificially constructed flow. This interpretation provides a means to construct numerical solutions to the adjoint equations that do not compromise the fully viscous nature of the problem. The algorithmic and computational aspects of solving the adjoint equations are addressed. The form of these set of equations is similar but not identical to the Navier-Stokes equations. In particular some issues related to boundary conditions and stability are discussed.
Efficient solution of turbulent incompressible separated flows
NASA Astrophysics Data System (ADS)
Michelassi, Vittorio; Martelli, Francesco
A computational method for incompressible separated flows based on two-dimensional approximate factorization is presented. Turbulence effects are accounted for by low-Reynolds number forms of the k-epsilon model. Mass conservation is enforced by the artificial compressibility method. Decoupling and coupling of the equations of motions with the turbulence model equations are investigated. Testing of the coupled solver showed no improvement in convergence or accuracy in comparison to the classical decoupled approach. The solver was then applied to several large-recirculation flows using a modified version of the low-Reynolds-number form of the k-epsilon model proposed by Chien and a two-layer version of the k-epsilon model introduced by Rodi. Both versions gave fast convergence rates and good agreement with experiments.
Algorithm 866: IFISS, a Matlab toolbox for modelling incompressible flow
Silvester, David J.
Additional Key Words and Phrases: Matlab, finite elements, incompressible flow, iterative solvers problems. It includes algorithms for discretization by mixed finite element methods and a posteriori errorAlgorithm 866: IFISS, a Matlab toolbox for modelling incompressible flow Howard C. Elman, Alison
Coarse Grain Parallel Finite Element Simulations for Incompressible Flows
Grant, P. W.
.F. Webster1 Institute of nonŁNewtonian Fluid Mechanics Department of Computer Science University of Wales in a sequential form for the simulation of incompressible Newtonian and non-Newtonian flows [1, 2]. Here University Uxbridge, Middlesex, UB8 3PH, UK Parallel simulation of incompressible fluid flows is considered
Supercomputing Aspects for Simulating Incompressible Flow
NASA Technical Reports Server (NTRS)
Kwak, Dochan; Kris, Cetin C.
The primary objective of this research is to support the design of liquid rocket systems for the Advanced Space Transportation System. Since the space launch systems in the near future are likely to rely on liquid rocket engines, increasing the efficiency and reliability of the engine components is an important task. One of the major problems in the liquid rocket engine is to understand fluid dynamics of fuel and oxidizer flows from the fuel tank to plume. Understanding the flow through the entire turbo-pump geometry through numerical simulation will be of significant value toward design. One of the milestones of this effort is to develop, apply and demonstrate the capability and accuracy of 3D CFD methods as efficient design analysis tools on high performance computer platforms. The development of the Message Passage Interface (MPI) and Multi Level Parallel (MLP) versions of the INS3D code is currently underway. The serial version of INS3D code is a multidimensional incompressible Navier-Stokes solver based on overset grid technology, INS3D-MPI is based on the explicit massage-passing interface across processors and is primarily suited for distributed memory systems. INS3D-MLP is based on multi-level parallel method and is suitable for distributed-shared memory systems. For the entire turbo-pump simulations, moving boundary capability and efficient time-accurate integration methods are built in the flow solver, To handle the geometric complexity and moving boundary problems, an overset grid scheme is incorporated with the solver so that new connectivity data will be obtained at each time step. The Chimera overlapped grid scheme allows subdomains move relative to each other, and provides a great flexibility when the boundary movement creates large displacements. Two numerical procedures, one based on artificial compressibility method and the other pressure projection method, are outlined for obtaining time-accurate solutions of the incompressible Navier-Stokes equations. The performance of the two methods is compared by obtaining unsteady solutions for the evolution of twin vortices behind a flat plate. Calculated results are compared with experimental and other numerical results. For an unsteady flow, which requires small physical time step, the pressure projection method was found to be computationally efficient since it does not require any subiteration procedure. It was observed that the artificial compressibility method requires a fast convergence scheme at each physical time step in order to satisfy the incompressibility condition. This was obtained by using a GMRES-ILU(0) solver in present computations. When a line-relaxation scheme was used, the time accuracy was degraded and time-accurate computations became very expensive.
Flight research on natural laminar flow applications
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.; Obara, Clifford J.
Natural laminar flow (NLF) is clearly one of the most potentially attractive drag reduction technologies by virtue of its relative simplicity. NLF is achieved passively, that is, by design of surface shapes to produce favorable pressure gradients. However, it is not without its challenges and limitations. This chapter describes the significant challenges to achieving and maintaining NLF and documents certain of the limitations for practical applications. A brief review of the history and of more recent NLF flight experiments is given, followed by a summary of lessons learned which are pertinent to future applications. The chapter also summarizes important progress in test techniques, particularly in flow visualization and hot-film techniques for boundary-layer measurements in flight.
Base pressure in laminar supersonic flow.
NASA Technical Reports Server (NTRS)
Messiter, A. F.; Hough, G. R.; Feo, A.
An asymptotic description is proposed for supersonic laminar flow over a wedge or a backward-facing step, for large Reynolds number and for a base or step height which is small compared with the boundary-layer length. The analysis is carried out for adiabatic wall conditions and a viscosity coefficient proportional to temperature. In a particular limit corresponding to a very thick boundary layer, a similarity law is obtained for the base pressure. For a thinner boundary layer an asymptotic form for the base pressure is obtained which shows the dependence on the parameters explicitly and which permits good agreement with experiment. This latter result is based on an inviscid-flow approximation for the corner expansion and for reattachment with viscous forces important primarily in a thin sublayer about the dividing streamline. A prediction of the pressure distribution at reattachment is given and the result is compared with experimental pressure distributions.
Durability of hybrid laminar flow control (HLFC) surfaces
Trevor Young; Brian Mahony; Bryan Humphreys; Ernst Totland; Alan McClafferty; Julie Corish
As a part of the European Commission sponsored HYLTEC (Hybrid Laminar Flow Technology) project, a SAAB 2000 aircraft ¢ fitted with a number of small laser drilled panels on the wing leading edge ¢ completed 20 months of routine service; the objective being to investigate contamination and durability aspects of Hybrid Laminar Flow Control (HLFC) suction surfaces. A post-flight test
Laminar flow control, 1976 - 1982: A selected annotated bibliography
M. H. Tuttle; D. V. Maddalon
Laminar Flow Control technology development has undergone tremendous progress in recent years as focused research efforts in materials, aerodynamics, systems, and structures have begun to pay off. A virtual explosion in the number of research papers published on this subject has occurred since interest was first stimulated by the 1976 introduction of NASA's Aircraft Energy Efficiency Laminar Flow Control Program.
Gliding swifts attain laminar flow over rough wings.
Lentink, David; de Kat, Roeland
Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089
Gliding Swifts Attain Laminar Flow over Rough Wings
Lentink, David; de Kat, Roeland
Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1¢2% of chord length on the upper surfaceŚ10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and durationŚsimilar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089
Advanced stability theory analyses for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
Recent developments of the SALLY computer code for stability analysis of laminar flow control wings are summarized. Extensions of SALLY to study three dimensional compressible flows, nonparallel and nonlinear effects are discussed.
Stability of the laminar flow on a body of revolution at incidence
NASA Astrophysics Data System (ADS)
Dovgal, A. V.; Zanin, B. Yu.; Sorokin, A. M.
An asymmetric incompressible gas flow past a body of revolution was studied in a subsonic wind tunnel. Characteristics of the velocity field at the stern of the experimental model, where a laminar boundary-layer separation and concomitant destabilization of the flow occur under axisymmetric conditions, were determined. Declination of the axis of symmetry of the body within several angular degrees results in a radical change of the time-average velocity field, the amplitude distribution of growing hydrodynamic disturbances, and their spectral distribution.
Progress in natural laminar flow research
NASA Technical Reports Server (NTRS)
Holmes, B. J.
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect debris in flight. This paper explains recent progress in our understanding of the achieveability and maintainability of NLF on modern airframe surfaces. This discussion explains why previous attempts to use NLF failed and what has changed regarding the three classical objections to NLF practicality. Future NASA research plans are described concerning exploring the limits of NLF usefulness, production tolerances, operational considerations, transition behavior and measurement methods, and NLF design applications.
Progress in natural laminar flow research
NASA Astrophysics Data System (ADS)
Holmes, B. J.
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect debris in flight. This paper explains recent progress in our understanding of the achieveability and maintainability of NLF on modern airframe surfaces. This discussion explains why previous attempts to use NLF failed and what has changed regarding the three classical objections to NLF practicality. Future NASA research plans are described concerning exploring the limits of NLF usefulness, production tolerances, operational considerations, transition behavior and measurement methods, and NLF design applications.
Toward a laminar-flow-control transport
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
Analyses were conducted to define a practical design for an advanced technology laminar flow control (LRC) transport for initial passenger operation in the early 1990's. Mission requirements, appropriate design criteria, and level of technology for the study aircraft were defined. The characteristics of the selected configuration were established, aircraft and LFC subsystems compatible with the mission requirements were defined, and the aircraft was evaluated in terms of fuel efficiency. A wing design integrating the LFC ducting and metering system into advanced composite wing structure was developed, manufacturing procedures for the surface panel design were established, and environmental and structural testing of surface panel components were conducted. Test results revealed a requirement for relatively minor changes in the manufacturing procedures employed, but have shown the general compatibility of both the selected design and the use of composite materials with the requirements of LFC wing surface panels.
Inductively coupled plasma torch with laminar flow cooling
Rayson, Gary D. (Las Cruces, NM); Shen, Yang (Las Cruces, NM)
An improved inductively coupled gas plasma torch. The torch includes inner and outer quartz sleeves and tubular insert snugly fitted between the sleeves. The insert includes outwardly opening longitudinal channels. Gas flowing through the channels of the insert emerges in a laminar flow along the inside surface of the outer sleeve, in the zone of plasma heating. The laminar flow cools the outer sleeve and enables the torch to operate at lower electrical power and gas consumption levels additionally, the laminar flow reduces noise levels in spectroscopic measurements of the gaseous plasma.
Direct numerical simulation of incompressible axisymmetric flows
NASA Astrophysics Data System (ADS)
Loulou, Patrick
In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities of importance in turbulence modeling, like the mean velocity, turbulent stresses, and all the terms in the Reynolds-stress balance equations. In addition, we will be interested in the evolution of large-scale structures that are common in free shear flow. The axisymmetric jet or wake is also a good problem in which to try the newly developed b-spline numerical method. Using b-splines as interpolating functions in the non-periodic direction offers many advantages. B-splines have local support, which leads to sparse matrices that can be efficiently stored and solved. Also, they offer spectral-like accuracy that are C(exp O-1) continuous, where O is the order of the spline used; this means that derivatives of the velocity such as the vorticity are smoothly and accurately represented. For purposes of validation against existing results, the present code will also be able to simulate internal flows (ones that require a no-slip boundary condition). Implementation of no-slip boundary condition is trivial in the context of the b-splines.
An immersed boundary method for time-dependant, three- dimensional, incompressible flows is presented in this paper. The incompressible Navier-Stokes equations are discretized using a low-diffusion flux splitting method for the inviscid fluxes and a second order central differenc...
F-111 TACT natural laminar flow glove flight results
NASA Technical Reports Server (NTRS)
Montoya, L. C.; Steers, L. L.; Trujillo, B.
Improvements in cruise efficiency on the order of 15 to 40% are obtained by increasing the extent of laminar flow over lifting surfaces. Two methods of achieving laminar flow are being considered, natural laminar flow and laminar flow control. Natural laminar flow (NLF) relies primarily on airfoil shape while laminar flow control involves boundary layer suction or blowing with mechanical devices. The extent of natural laminar flow that could be achieved with consistency in a real flight environment at chord Reynolds numbers in the range of 30 x 10(6) power was evaluated. Nineteen flights were conducted on the F-111 TACT airplane having a NLF airfoil glove section. The section consists of a supercritical airfoil providing favorable pressure gradients over extensive portions of the upper and lower surfaces of the wing. Boundary layer measurements were obtained over a range of wing leading edge sweep angles at Mach numbers from 0.80 to 0.85. Data were obtained for natural transition and for a range of forced transition locations over the test airfoil.
A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for high Reynolds number laminar flows
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.
Natural laminar flow airfoil analysis and trade studies
NASA Technical Reports Server (NTRS)
An analysis of an airfoil for a large commercial transport cruising at Mach 0.8 and the use of advanced computer techniques to perform the analysis are described. Incorporation of the airfoil into a natural laminar flow transport configuration is addressed and a comparison of fuel requirements and operating costs between the natural laminar flow transport and an equivalent turbulent flow transport is addressed.
Supersonic laminar flow development in a square duct
NASA Technical Reports Server (NTRS)
Davis, D. O.; Gessner, F. B.; Kerlick, G. D.
Supersonic laminar flow development in a constant-area square duct exhibits as one of its distinguishing features the formation of two contrarotating secondary flow vortices centered about the corner bisector. This phenomenon does not occur in unbounded corner flow. The secondary flow causes an outward bulging of total pressure contours in the vicinity of the corner bisector for wholly attached flow conditions.
Assessment of the National Transonic Facility for Laminar Flow Testing
NASA Technical Reports Server (NTRS)
Crouch, Jeffrey D.; Sutanto, Mary I.; Witkowski, David P.; Watkins, A. Neal; Rivers, Melissa B.; Campbell, Richard L.
A transonic wing, designed to accentuate key transition physics, is tested at cryogenic conditions at the National Transonic Facility at NASA Langley. The collaborative test between Boeing and NASA is aimed at assessing the facility for high-Reynolds number testing of configurations with significant regions of laminar flow. The test shows a unit Reynolds number upper limit of 26 M/ft for achieving natural transition. At higher Reynolds numbers turbulent wedges emanating from the leading edge bypass the natural transition process and destroy the laminar flow. At lower Reynolds numbers, the transition location is well correlated with the Tollmien-Schlichting-wave N-factor. The low-Reynolds number results suggest that the flow quality is acceptable for laminar flow testing if the loss of laminar flow due to bypass transition can be avoided.
Experimental transition and boundary-layer stability analysis for a slotted swept laminar flow control airfoil
NASA Technical Reports Server (NTRS)
Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.
A swept, supercritical laminar flow control (LFC) airfoil designated NASA SCLFC(1)-0513F was tested at subsonic and transonic speeds in the NASA Langley eight-foot Transonic Pressure Tunnel. This paper examines Tollmien-Schlichting and crossflow disturbance amplification for this airfoil using the linear stability method. The design methodology using linear stability analysis is evaluated and the results of the incompressible and compressible methods are compared. Experimental data on the swept, supercritical LFC airfoil and reference wind tunnel and flight results are used to correlate and evaluate the N-factor method for transition prediction over a speed range M(infinity) from zero to one.
Application of natural laminar flow to a supersonic transport concept
NASA Technical Reports Server (NTRS)
Fuhrmann, Henri D.
Results are presented of a preliminary investigation into an application of supersonic natural laminar flow (NLF) technology for a high speed civil transport (HSCT) configuration. This study focuses on natural laminar flow without regard to suction devices which are required for laminar flow control (LFC) or hybrid laminar flow control (HLFC). An HSCT design is presented with a 70 deg inboard leading-edge sweep and a 20 deg leading-edge outboard crank to obtain NLF over the outboard crank section. This configuration takes advantage of improved subsonic performance and NLF on the low-sweep portion of the wing while minimizing the wave drag and induced drag penalties associated with low-sweep supersonic cruise aircraft. In order to assess the benefits of increasing natural laminar flow wetted area, the outboard low-sweep wing area is parametrically increased. Using a range of supersonic natural laminar flow transition Reynolds numbers, these aircraft are then optimized and sized for minimum take-off gross weight (TOGW) subject to mission constraints. Results from this study indicate reductions in TOGW for the NLF concepts, due mainly to reductions in wing area and total wing weight. Furthermore, significant reductions in block fuel are calculated throughout the range of transition Reynolds numbers considered. Observations are made on the benefits of unsweeping the wingtips with all turbulent flow.
Laminar flow integration: Flight tests status and plans
R. D. Wagner; D. F. Fisher; M. C. Fischer; D. W. Bartlett; R. R. Meyer Jr.
Under the Aircraft Energy Efficiency - Laminar Flow Control Program, there are currently three flight test programs under way to address critical issues concerning laminar flow technology application to commercial transports. The Leading-Edge Flight Test (LEFT) with a JetStar aircraft is a cooperative effort with the Ames\\/Dryden Flight Research Facility to provide operational experience with candidate leading-edge systems representative of
General Equation Set Solver for Compressible and Incompressible Turbomachinery Flows
NASA Technical Reports Server (NTRS)
Sondak, Douglas L.; Dorney, Daniel J.
Turbomachines for propulsion applications operate with many different working fluids and flow conditions. The flow may be incompressible, such as in the liquid hydrogen pump in a rocket engine, or supersonic, such as in the turbine which may drive the hydrogen pump. Separate codes have traditionally been used for incompressible and compressible flow solvers. The General Equation Set (GES) method can be used to solve both incompressible and compressible flows, and it is not restricted to perfect gases, as are many compressible-flow turbomachinery solvers. An unsteady GES turbomachinery flow solver has been developed and applied to both air and water flows through turbines. It has been shown to be an excellent alternative to maintaining two separate codes.
Incipient particle motion in laminar shear flows
NASA Astrophysics Data System (ADS)
RodrĒguez Agudo, Josķ Alberto; Wierschem, Andreas
We study experimentally the critical conditions for incipient motion of spherical particles deposited on a regular substrate under laminar flow conditions. The substrates consist of a monolayer of wall-fixed spheres uniformly sized and regularly arranged in triangular and quadratic configurations. To highlight the effects of exposure, the distance between the substrate spheres is varied in the quadratic arrangement. We found that for particle Reynolds numbers of order one and smaller, the critical Shields parameter is independent from the particle density and from the particle Reynolds numbers but it depends significantly on the geometry of the substrate. We show how different geometrical parameters like the particle arrangement and exposure affect the critical Shields parameter. We particularly focus on the effect of neighboring particles on the onset of particle motion. Unlike single rolling particles, we observe switching between rolling and sliding motion as a consequence of friction between the moving neighbors. In our experiments, this two-particle interaction is the basic difference between the incipient motion of a single and multiple particles, resulting in a significant increment of the critical Shields number.
Acoustic waves superimposed on incompressible flows
NASA Technical Reports Server (NTRS)
Hodge, Steve
The use of incompressible approximations in deriving solutions to the Lighthill wave equation was investigated for problems where an analytical solution could be found. A particular model problem involves the determination of the sound field of a spherical oscillating bubble in an ideal fluid. It is found that use of incompressible boundary conditions leads to good approximations in the important region of high acoustic wave number.
Design of fuselage shapes for natural laminar flow
NASA Astrophysics Data System (ADS)
Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.
Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.
Design of fuselage shapes for natural laminar flow
NASA Technical Reports Server (NTRS)
Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.
Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.
Selected experiments in laminar flow: An annotated bibliography
NASA Technical Reports Server (NTRS)
Drake, Aaron; Kennelly, Robert A., Jr.
Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments.
The stability of the flow in a laminar separation bubble
NASA Astrophysics Data System (ADS)
Niew, Tai Ran
This dissertation reports a study into the underlying concepts used to analyze incompressible laminar separation bubbles. The suggestion that absolute instability could play a role in bubble flows was further developed, and was the focal point of this project. From a review of previous work and preliminary experiments on a backward faxing step, it was suggested that for some bubbles the reattachment region of the flow field could be absolutely unstable. A cornerstone of this view is that the completion of transition is not a prerequisite for the start of reattachment; and that a more fundamental mechanism involves significant interaction between the two processes. This concept was first tested by solving the eigenvalue problem of the Orr-Sommerfeld equation for a family of reverse flow profiles. The results indicated that with sufficient reverse flow, wall-bounded separated shear-layers that are similar to experimentally measured profiles can be absolutely unstable. This is consistent with the hypothesis outlined above. The numerical study also showed that for convectively unstable profiles, the predominant parameter that determines the spatial growth rate of instability waves is the distance of the separated shear layer from the wall. Furthermore, viscosity only has a weak effect on the stability characteristics of both absolutely and convectively unstable profiles at generic bubble Reynolds numbers. Experiments were then carried out on the flow behind a backward facing step using artificially excited instability waves, and the key issues in formulating a conceptually robust experimental method to test the above hypothesis was discussed. If the forcing was carried out with a non-acoustic source, it was shown that the use of impulse excitation could provide a rigorous procedure. Two qualitatively different transition mechanisms, 'wave' and 'spot' type, were also observed in these experiments. A new perspective of bubble behavior was then developed that considered the interaction of turbulent breakdown, reattachment and inducing of reverse flow. The concept of the absolutely unstable reattachment region is an integral part of this view, and the analysis was used to account for the different breakdown processes detected. Based on this alternative framework for analyzing bubble flows, a comprehensive list of fresh areas for future research was also suggested.
Statistical theory of turbulent incompressible multimaterial flow
Kashiwa, B.
Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of kappa-epsilon modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy kappa, and the rate of fluctuational energy dissipation epsilon, for each material. Hence a set of kappa and epsilon equations must be solved, together with mean mass and momentum conservation equations, for each material. Both kappa and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe.
Numerical simulation of incompressible viscous flow in deforming domains
Colella, Phillip; Trebotich, David P.
We present a second-order accurate finite difference method for numerical solution of the incompressible Navier-Stokes equations in deforming domains. Our approach is a generalization of the Bell-Colella-Glaz predictor¢corrector method for incompressible flow. In order to treat the time-dependence and inhomogeneities in the incompressibility constraint introduced by presence of deforming boundaries, we introduce a nontrivial splitting of the velocity field into vortical and potential components to eliminate the inhomogeneous terms in the constraint and a generalization of the Bell-Colella-Glaz algorithm to treat time-dependent constraints. The method is second-order accurate in space and time, has a time step constraint determined by the advective Colella-Friedrichs-Lewy condition, and requires the solution of well behaved linear systems amenable to the use of fast iterative methods. We demonstrate the method on the specific example of viscous incompressible flow in an axisymmetric deforming tube. PMID:10318891
Numerical studies of heat transfer enhancements in laminar separated flows
Chung, Yongmann M.
heat transfer enhancements in grooved channel and sharp 180░ bend flows of especial relevanceNumerical studies of heat transfer enhancements in laminar separated flows Yongmann M. Chung not always be valid over a significant system extent. For the bend flow, heat transfer enhancements due
Model of Transition from Laminar to Turbulent Flow
Hidesada Kanda
For circular pipe flows, a model of transition from laminar to turbulent flow has already been proposed and the minimum critical Reynolds number of approximately 2040 was obtained (Kanda, 1999). In order to prove the validity of the model, another verification is required. Thus, for plane Poiseuille flow, results of previous investigations were studied, focusing on experimental data on the
Laminar and intermittent flow in a tilted heat pipe.
Rusaouen, E; Riedinger, X; Tisserand, J-C; Seychelles, F; Salort, J; Castaing, B; ChillÓ, F
Heat transfer measurements performed by Riedinger et al. (Phys. Fluids, 25, 015117 (2013)) showed that in an inclined channel, heated from below and cooled from above with adiabatic walls, the flow is laminar or intermittent (local bursts can occur in the laminar flow) when the inclination angle is sufficiently high and the applied power sufficiently low. In this case, gravity plays a crucial role in the characteristics of the flow. In this paper, we present velocity measurements, and their derived tensors, obtained with Particle Image Velocimetry inside the channel. We, also, propose a model derived from a jet interpretation of the flow. Comparison between experiment and model shows a fair agreement. PMID:24464137
Brief history of laminar flow clean room systems
Whitfield, W J
This paper reviews the development and evolution of laminar flow clean rooms and hoods and describes the underlying principles and rationales associated with development of this type of clean room system and Federal Standard No. 209. By the mid 1970's, over a thousand hospitals in the US had installed laminar flow equipment in operating rooms. During the past several years a great deal of attention has been focused on conserving energy in clean rooms. Some gains in energy conservation have been achieved by improved design, off hours shutdown, and closer evaluation of requirements for clean rooms. By the early 1970's, the laminar flow principle had been carried from the Laboratory and applied to production hardware to create a mature industry producing and marketing a variety of laminar flow equipment in less than 10 years time. This achievement was made possible by literally dozens of persons in industry, government, military, and private individuals who developed hardware, added numerous innovations, and had the foresight to apply the technology to many fields other than industrial clean rooms. Now, with laminar flow devices available, class 100 levels are readily achievable and maintained, and at the same time require fewer operating restrictions than previously possible.
J. P. Van Doormaal; G. D. Raithby
Variations of the SIMPLE method of Patankar and Spalding have been widely used over the past decade to obtain numerical solutions to problems involving incompressible flows. The present paper shows several modifications to the method which both simplify its implementation and reduce solution costs. The performances of SIMPLE, SIMPLER, and SIMPLEC (the present method) are compared for two recirculating flow
Finite-difference immersed boundary method consistent with wall conditions for incompressible turbulent flow simulations
Ikeno, Tsutomu [Nuclear Fuel Industries, Ltd., 950, Asashiro Nishi, 1-Chome, Kumatori-Cho, Sennan-Gun, Osaka, 590-0481 (Japan)], E-mail: email@example.com; Kajishima, Takeo [Department of Mechanical Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871 (Japan)
An immersed boundary method to achieve the consistency with a desired wall velocity was developed. Existing schemes of immersed boundary methods for incompressible flow violate the wall condition in the discrete equation system during time-advancement. This problem arises from the inconsistency of the pressure with the velocity interpolated to represent the solid wall, which does not coincide with the computational grid. The numerical discrepancy does not become evident in the laminar flow simulation but in the turbulent flow simulation. To eliminate this inconsistency, a modified pressure equation based on the interpolated pressure gradient was derived for the spatial second-order discrete equation system. The conservation of the wall condition, mass, momentum and energy in the present method was theoretically demonstrated. To verify the theory, large eddy simulations for a plane channel, circular pipe and nuclear rod bundle were successfully performed. Both these theoretical and numerical validations improve the reliability and the applicability of the immersed boundary method.
Nonstationary flow of a viscous incompressible fluid past an airfoil
NASA Astrophysics Data System (ADS)
Zakharenkov, M. N.
The difficulties involved in the calculation of separated flow past airfoils are examined with particular reference to separated flow of a viscous incompressible fluid past a 12-percent Joukowski profile at Reynolds numbers of 10 exp 3 and 10 exp 4 and angles of attack of 15 and 5 degrees, respectively. The examples considered here illustrate the possibilities of computational aerodynamics in the study of vortex flows, formation of coherent structures, and flow separation.
A Numerical Method for Incompressible Flow with Heat Transfer
NASA Technical Reports Server (NTRS)
Sa, Jong-Youb; Kwak, Dochan
A numerical method for the convective heat transfer problem is developed for low speed flow at mild temperatures. A simplified energy equation is added to the incompressible Navier-Stokes formulation by using Boussinesq approximation to account for the buoyancy force. A pseudocompressibility method is used to solve the resulting set of equations for steady-state solutions in conjunction with an approximate factorization scheme. A Neumann-type pressure boundary condition is devised to account for the interaction between pressure and temperature terms, especially near a heated or cooled solid boundary. It is shown that the present method is capable of predicting the temperature field in an incompressible flow.
A monolithic mass tracking formulation for bubbles in incompressible flow
Aanjaneya, Mridul, E-mail: email@example.com; Patkar, Saket, E-mail: firstname.lastname@example.com; Fedkiw, Ronald, E-mail: email@example.com
We devise a novel method for treating bubbles in incompressible flow that relies on the conservative advection of bubble mass and an associated equation of state in order to determine pressure boundary conditions inside each bubble. We show that executing this algorithm in a traditional manner leads to stability issues similar to those seen for partitioned methods for solid¢fluid coupling. Therefore, we reformulate the problem monolithically. This is accomplished by first proposing a new fully monolithic approach to coupling incompressible flow to fully nonlinear compressible flow including the effects of shocks and rarefactions, and then subsequently making a number of simplifying assumptions on the air flow removing not only the nonlinearities but also the spatial variations of both the density and the pressure. The resulting algorithm is quite robust, has been shown to converge to known solutions for test problems, and has been shown to be quite effective on more realistic problems including those with multiple bubbles, merging and pinching, etc. Notably, this approach departs from a standard two-phase incompressible flow model where the air flow preserves its volume despite potentially large forces and pressure differentials in the surrounding incompressible fluid that should change its volume. Our bubbles readily change volume according to an isothermal equation of state.
Roughness and waviness requirements for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Obara, Clifford J.; Holmes, Bruce J.
Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.
Roughness and waviness requirements for laminar flow surfaces
NASA Astrophysics Data System (ADS)
Obara, Clifford J.; Holmes, Bruce J.
Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.
Flight Tests of a Supersonic Natural Laminar Flow Airfoil
NASA Technical Reports Server (NTRS)
Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.
A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80-inch (203 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15B airplane. The wing was designed with a leading edge sweep of effectively 0 deg to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow wings.
Computational Optimization of a Natural Laminar Flow Experimental Wing Glove
NASA Technical Reports Server (NTRS)
Hartshom, Fletcher
Computational optimization of a natural laminar flow experimental wing glove that is mounted on a business jet is presented and discussed. The process of designing a laminar flow wing glove starts with creating a two-dimensional optimized airfoil and then lofting it into a three-dimensional wing glove section. The airfoil design process does not consider the three dimensional flow effects such as cross flow due wing sweep as well as engine and body interference. Therefore, once an initial glove geometry is created from the airfoil, the three dimensional wing glove has to be optimized to ensure that the desired extent of laminar flow is maintained over the entire glove. TRANAIR, a non-linear full potential solver with a coupled boundary layer code was used as the main tool in the design and optimization process of the three-dimensional glove shape. The optimization process uses the Class-Shape-Transformation method to perturb the geometry with geometric constraints that allow for a 2-in clearance from the main wing. The three-dimensional glove shape was optimized with the objective of having a spanwise uniform pressure distribution that matches the optimized two-dimensional pressure distribution as closely as possible. Results show that with the appropriate inputs, the optimizer is able to match the two dimensional pressure distributions practically across the entire span of the wing glove. This allows for the experiment to have a much higher probability of having a large extent of natural laminar flow in flight.
Flight tests of a supersonic natural laminar flow airfoil
NASA Astrophysics Data System (ADS)
Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.
A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80?inch (203?cm) chord and 40?inch (102?cm) span article mounted on the centerline store location of an F-15B airplane. The test article was designed with a leading edge sweep of effectively 0░ to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate that the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, was similar to that of subsonic natural laminar flow wings.
Design of a hybrid laminar flow control nacelle
NASA Technical Reports Server (NTRS)
Wie, Yong-Sun; Collier, Fayette S., Jr.; Wagner, Richard D.; Viken, Jeffery K.; Pfenninger, Werner
Consideration is given to the potential application of hybrid-laminar-flow control to the external surface of a modern, high-bypass-ratio (HBR) turbofan engine nacelle. With the advent of advanced ultra-HBR fans (with bypass ratios of 10-15), the wetted areas of these nacelles approach 10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies on an advanced twin-engine transport configuration are presented to determine potential benefits in terms of reduced fuel consumption.
CFD Investigations of a Transonic Swept-Wing Laminar Flow Control Flight ExperimentĀ
Neale, Tyler P.
Laminar flow control has been studied for several decades in an effort to achieve higher efficiencies for aircraft. Successful implementation of laminar flow control technology on transport aircraft could significantly ...
A computer code for three-dimensional incompressible flows using nonorthogonal body-fitted coordinate systems
NASA Technical Reports Server (NTRS)
Chen, Y. S.
In this report, a numerical method for solving the equations of motion of three-dimensional incompressible flows in nonorthogonal body-fitted coordinate (BFC) systems has been developed. The equations of motion are transformed to a generalized curvilinear coordinate system from which the transformed equations are discretized using finite difference approximations in the transformed domain. The hybrid scheme is used to approximate the convection terms in the governing equations. Solutions of the finite difference equations are obtained iteratively by using a pressure-velocity correction algorithm (SIMPLE-C). Numerical examples of two- and three-dimensional, laminar and turbulent flow problems are employed to evaluate the accuracy and efficiency of the present computer code. The user's guide and computer program listing of the present code are also included.
An isoparametric spectral element method in simulation of incompressible complex flows
NASA Astrophysics Data System (ADS)
Korczak, Karol Z.
An isoparametric spectral element method, a high-order finite element technique for solving the incompressible general Navier-Stokes equations, is briefly introduced (general 3-D formulation). The accuracy of the method and its dependence on a choice of collocating points is demonstrated on a Poisson equation case. For inflow-outflow problems, it has been shown that the natural (zero-gradient) boundary conditions at outflow perform reasonably well. The high convergence of this technique, combined with very small numerical dissipation and dispersion errors, allows realistic direct simulation of highly-unsteady and turbulent flows. Here, a numerical study of a turbulent mixing layer (from a splitter plate) is presented. In this application, in addition to the high accuracy, the isoparametric spectral element algorithm permits geometrical singularities in the computational domain, thus allowing a laminar boundary layer flow over the splitter plate, transition, and evolution of turbulent structures to be included in the simulation process.
Calibration of laminar flow meters for process gases
John D. Wright; Thiago Cobu; Robert F. Berg; Michael R. Moldover
We calibrated three models of commercially-manufactured, laminar flow meters (LFMs) at four pressures (100, 200, 300, and 400 kPa) with five gases (N2, Ar, He, CO2, and SF6) over a 10:1 flow range using NISTÆs primary flow standards as references. We combined three items: (1) the calibration data acquired with N2, (2) gas-property data from NISTÆs database REFPROP 9.0, and
The incompressible Bernoulli equation is an analytical relationship between pressure, kinetic energy, and potential energy. As perhaps the simplest and most useful statement for describing laminar flow, it buttresses numerous incompressible flow models that have been developed ...
F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment
NASA Technical Reports Server (NTRS)
Anders, Scott G.; Fischer, Michael C.
The F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment was part of the NASA High-Speed Research Program. The goal of the experiment was to demonstrate extensive laminar flow, to validate computational fluid dynamics (CFD) codes and design methodology, and to establish laminar flow control design criteria. Topics include the flight test hardware and design, airplane modification, the pressure and suction distributions achieved, the laminar flow achieved, and the data analysis and code correlation.
Blow up criterion for incompressible nematic liquid crystal flows
Guochun Wu
In this paper, we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible, nematic liquid crystal materials in dimension three. We establish a criterion for possible breakdown of such solutions at a finite time. More precisely, if $(u,d)$ is smooth up to time $T$ provided that $\\int_0^T|\
An update on projection methods for transient incompressible viscous flow
Gresho, P.M.; Chan, S.T.
Introduced in 1990 was the biharmonic equation (for the pressure) and the concomitant biharmonic miracle when transient incompressible viscous flow is solved approximately by a projection method. Herein is introduced the biharmonic catastrophe that sometimes occurs with these same projection methods.
NASA Technical Reports Server (NTRS)
Albers, J. A.
This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.
Application of laminar flow control to supersonic transport configurations
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Nagel, A. L.
The feasibility and impact of implementing a laminar flow control system on a supersonic transport configuration were investigated. A hybrid laminar flow control scheme consisting of suction controlled and natural laminar flow was developed for a double-delta type wing planform. The required suction flow rates were determined from boundary layer stability analyses using representative wing pressure distributions. A preliminary design of structural modifications needed to accommodate suction through a perforated titanium skin was carried out together with the ducting and systems needed to collect, compress and discharge the suction air. The benefits of reduced aerodynamic drag were weighed against the weight, volume and power requirement penalties of suction system installation in a mission performance and sizing program to assess the net benefits. The study showed a feasibility of achieving significant laminarization of the wing surface by use of a hybrid scheme, leading to an 8.2 percent reduction in the cruise drag. This resulted in an 8.5 percent reduction in the maximum takeoff weight and a 12 percent reduction in the fuel burn after the inclusion of the LFC system installation penalties. Several research needs were identified for a resolution of aerodynamics, structural and systems issues before these potential benefits could be realized in a practical system.
Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam
Maschke, A.W.
A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow through the assembly.
Numerical Simulation of Low-Mach-Number Laminar Mixing and Reacting Flows Using a Dual-Purpose Pressure-Based Algorithm
Hamidreza Ebrahimi-Kebria; Masoud Darbandi; Seyed Farid Hosseinizadeh
Benefitting from an analogy between compressible and incompressible governing equations, a novel dual-purpose, pressure-based finite-volume algorithm is suitably extended to simulate laminar mixing and reacting flows in low-Mach-number regimes. In our test cases, the Mach number is as high as 0.00326. Definitely, such low-Mach-number flows cannot be readily solved by either regular density-based solvers or most of their extensions. To
A segregated implicit pressure projection method for incompressible flows
NASA Astrophysics Data System (ADS)
Utnes, T.
In this paper a segregated, implicit projection method is presented and investigated. Although high-Reynolds, turbulent flow has been a motivating factor, the present study is mainly restricted to the incompressible Navier-Stokes equations. The proposed method is analyzed for properties like stability, accuracy and consistency, aided by some test examples. In addition, two different flow cases are simulated to evaluate the ability and efficiency of the method compared with other results.
Conservative properties of finite difference schemes for incompressible flow
NASA Technical Reports Server (NTRS)
Morinishi, Youhei
The purpose of this research is to construct accurate finite difference schemes for incompressible unsteady flow simulations such as LES (large-eddy simulation) or DNS (direct numerical simulation). In this report, conservation properties of the continuity, momentum, and kinetic energy equations for incompressible flow are specified as analytical requirements for a proper set of discretized equations. Existing finite difference schemes in staggered grid systems are checked for satisfaction of the requirements. Proper higher order accurate finite difference schemes in a staggered grid system are then proposed. Plane channel flow is simulated using the proposed fourth order accurate finite difference scheme and the results compared with those of the second order accurate Harlow and Welch algorithm.
Adaptive ANOVA decomposition of stochastic incompressible and compressible flows
NASA Astrophysics Data System (ADS)
Yang, Xiu; Choi, Minseok; Lin, Guang; Karniadakis, George Em
Realistic representation of stochastic inputs associated with various sources of uncertainty in the simulation of fluid flows leads to high dimensional representations that are computationally prohibitive. We investigate the use of adaptive ANOVA decomposition as an effective dimension-reduction technique in modeling steady incompressible and compressible flows with nominal dimension of random space up to 100. We present three different adaptivity criteria and compare the adaptive ANOVA method against sparse grid, Monte Carlo and quasi-Monte Carlo methods to evaluate its relative efficiency and accuracy. For the incompressible flow problem, the effect of random temperature boundary conditions (modeled as high-dimensional stochastic processes) on the Nusselt number is investigated for different values of correlation length. For the compressible flow, the effects of random geometric perturbations (simulating random roughness) on the scattering of a strong shock wave is investigated both analytically and numerically. A probabilistic collocation method is combined with adaptive ANOVA to obtain both incompressible and compressible flow solutions. We demonstrate that for both cases even draconian truncations of the ANOVA expansion lead to accurate solutions with a speed-up factor of three orders of magnitude compared to Monte Carlo and at least one order of magnitude compared to sparse grids for comparable accuracy.
Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations
NASA Technical Reports Server (NTRS)
Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.
Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.
Solution for laminar natural convection flows in a square cavity with temperature dependent viscosity
Sanchez, J.G. [Parsons Brinckerhoff, New York, NY (United States)
This paper presents an examination of numerical results for the buoyancy-driven convection heat transfer problem, in a two-dimensional enclosure under steady-state, laminar, incompressible, and temperature dependent viscosity fluid flow conditions. The vertical walls are exposed to different temperatures and the top and bottom are insulated. Rayleigh numbers of 10{sup 4}, 10{sup 5}, and 10{sup 6} are considered. Specific heat, thermal conductivity, and the thermal expansion coefficient are assumed constant. Density variation is included using the Oberbeck-Boussinesq approximation. The results are obtained using the SIMPLEC solution technique based on a power-law, finite-volume discretization scheme. The hydrodynamic and thermal fields are presented at various locations in the enclosures.
to transitions to turbulence in rotating flows and to design corresponding dynamic control mechanisms ... The considerations in this study will provide a basic understanding of .... appealing in this case because of its ability to resolve thin boundary layers of viscous flows with ..... are of current research interest. The LegendreĀ...
Direct numerical simulation of `short' laminar separation bubbles with turbulent reattachment
M. Alam; N. D. Sandham
Direct numerical simulation of the incompressible Navier Stokes equations is used to study flows where laminar boundary-layer separation is followed by turbulent reattachment forming a closed region known as a laminar separation bubble. In the simulations a laminar boundary layer is forced to separate by the action of a suction profile applied as the upper boundary condition. The separated shear
Direct numerical simulation of 'short' laminar separation bubbles with turbulent reattachmenty
Direct numerical simulation of the incompressible Navier{Stokes equations is used to study flows where laminar boundary-layer separation is followed by turbulent reattachment forming a closed region known as a laminar separation bubble. In the simulations a laminar boundary layer is forced to separate by the action of a suction prole applied as the upper boundary condition. The separated shear layer
Incompressible viscous flow simulations of the NFAC wind tunnel
NASA Technical Reports Server (NTRS)
Champney, Joelle Milene
The capabilities of an existing 3-D incompressible Navier-Stokes flow solver, INS3D, are extended and improved to solve turbulent flows through the incorporation of zero- and two-equation turbulence models. The two-equation model equations are solved in their high Reynolds number form and utilize wall functions in the treatment of solid wall boundary conditions. The implicit approximate factorization scheme is modified to improve the stability of the two-equation solver. Applications to the 3-D viscous flow inside the 80 by 120 feet open return wind tunnel of the National Full Scale Aerodynamics Complex (NFAC) are discussed and described.
RIPPLE: A new model for incompressible flows with free surfaces
Kothe, D.B.; Mjolsness, R.C.
A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the Continuum Surface Force (CSF) model which represents surface tension as a (strongly) localized volume force. Other features include a high-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE'S unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods. 17 refs., 7 figs.
Mathematical aspects of finite element methods for incompressible viscous flows
NASA Technical Reports Server (NTRS)
Gunzburger, M. D.
Mathematical aspects of finite element methods are surveyed for incompressible viscous flows, concentrating on the steady primitive variable formulation. The discretization of a weak formulation of the Navier-Stokes equations are addressed, then the stability condition is considered, the satisfaction of which insures the stability of the approximation. Specific choices of finite element spaces for the velocity and pressure are then discussed. Finally, the connection between different weak formulations and a variety of boundary conditions is explored.
Gyrotactic trapping in laminar and turbulent Kolmogorov flow
Francesco Santamaria; Filippo De Lillo; Massimo Cencini; Guido Boffetta
Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases we show that TPLs become transient, and we characterize their persistence.
Acoustic effects on profile drag of a laminar flow airfoil
NASA Astrophysics Data System (ADS)
Shearin, John G.; Jones, Michael G.; Baals, Robert A.
A two-dimensional laminar flow airfoil (NLF-0414) was subjected to high-intensity sound (pure tones and white noise) over a frequency range of 2 to 5 kHz, while immersed in a flow of 240 ft/sec (Rn of 3 million) in a quiet flow facility. Using a wake-rake, wake dynamic pressures were determined and the deficit in momentum was used to calculate a two dimensional drag coefficient. Significant increases in drag were observed when the airfoil was subjected to the high intensity sound at critical sound frequencies. However, the increased drag was not accompanied by movement of the transition location.
Acoustic effects on profile drag of a laminar flow airfoil
NASA Technical Reports Server (NTRS)
Shearin, John G.; Jones, Michael G.; Baals, Robert A.
A two-dimensional laminar flow airfoil (NLF-0414) was subjected to high-intensity sound (pure tones and white noise) over a frequency range of 2 to 5 kHz, while immersed in a flow of 240 ft/sec (Rn of 3 million) in a quiet flow facility. Using a wake-rake, wake dynamic pressures were determined and the deficit in momentum was used to calculate a two dimensional drag coefficient. Significant increases in drag were observed when the airfoil was subjected to the high intensity sound at critical sound frequencies. However, the increased drag was not accompanied by movement of the transition location.
Making Large Suction Panels For Laminar-Flow Control
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.
Perforated titanium panels used to identify and resolve issues related to manufacture. Recently, relatively large suction panels with aerodynamically satisfactory surface perforations and with surface contours and smoothness characteristics necessary for Laminar-Flow Control (LFC) designed, fabricated, and tested. Requirements of production lines for commercial transport airplanes carefully considered in development of panels. Sizes of panels representative of what is used on wing of commercial transport airplane. Tests of perforated panels in transonic wind tunnel demonstrated aerodynamic stability at flight mach numbers.
Distributed acoustic receptivity in laminar flow control configurations
Meelan Choudhari
A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied within the Orr¢Sommerfeld framework, by developing a suitable extension of the Goldstein¢Ruban theory for receptivity due to localized disturbances on the airfoil surface. One advantage of the proposed method is that it easily permits the prediction of receptivity due to a
Distributed acoustic receptivity in laminar flow control configurations
Meelan Choudhari
A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied, within the Orr-Sommerfield framework, by a suitable extension of the Goldstein-Ruban theory for receptivity due to localized disturbances on the airfoil surface. The results, thus, complement the earlier work on the receptivity produced by local variations in the surface suction and\\/or
Aerodynamic Design for Swept-wing Laminar FlowĀ
Belisle, Michael Joseph
Improvement (AFRL/NGC) AFRL Air Force Research Laboratory ATTAS Advanced Technologies Testing Aircraft System (German Aerospace Center) BL Wing buttock line, measured in inches from aircraft centerline CAD Computer-aided design CC Complex conjugate CFD... PSE Parabolized stability equations xi RMS Root-mean-square SARGE Subsonic Aircraft Roughness Glove Experiment SCRAT Subsonic Research Aircraft Testbed SWIFT Swept-Wing In-Flight Testing (AFRL/TAMU) SWLFC Swept-wing laminar flow control TAMU Texas A...
Experimental investigation of oxide nanofluids laminar flow convective heat transfer
S. Zeinali Heris; S. Gh. Etemad; M. Nasr Esfahany
In the present investigation nanofluids containing CuO and Al2O3 oxide nanoparticles in water as base fluid in different concentrations produced and the laminar flow convective heat transfer through circular tube with constant wall temperature boundary condition were examined. The experimental results emphasize that the single phase correlation with nanofluids properties (Homogeneous Model) is not able to predict heat transfer coefficient
Fully elliptic incompressible flow calculations on regular grid by a new pressure substitution method
NASA Technical Reports Server (NTRS)
Hobson, G. V.; Lakshminarayana, B.
A new method is presented for the solution of incompressible flow in generalized coordinates. This method is based on the substitution of the pressure weighted form of the momentum equations into the continuity equation. The algorithm is rigorously derived and a Fourier analysis is used to assess its suitability to act as an error smoother. Linear stability analysis results indicate that the performance of the new pressure substitution method (PSM) and the pressure correction method (PCM) is about the same at low Reynolds numbers, with no significant pressure gradient. At high Reynolds numbers the PSM shows much faster convergence. Likewise prediction of various flows indicate that the PSM has better accuracy for high Reynolds number flows with significant pressure gradients. Since most practical aerodynamic flows have significant pressure gradients, the PSM seems to be attractive for such flows. Solutions for both laminar and turbulent flow are compared with the experimental data. A two-equation low Reynolds number turbulence model is used to resolve the turbulent flowfield.
Laminar flow of two miscible fluids in a simple network
NASA Astrophysics Data System (ADS)
Karst, Casey M.; Storey, Brian D.; Geddes, John B.
When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow can demonstrate multiple equilibria. The paper describes a theoretical and experimental investigation of the laminar flow of two miscible Newtonian fluids of different density and viscosity through a simple network. The fluids stratify due to gravity and remain as nearly distinct phases with some mixing occurring only by diffusion. This fluid system has the advantage that it is easily controlled and modeled, yet contains the key ingredients for network nonlinearities. Experiments and 3D simulations are first used to explore how phases distribute at a single T-junction. Once the phase separation at a single junction is known, a network model is developed which predicts multiple equilibria in the simplest of networks. The existence of multiple stable equilibria is confirmed experimentally and a criterion for existence is developed. The network results are generic and could be applied to or found in different physical systems.
Viscous Incompressible Flow Computations for 3-D Steady and Unsteady Flows
NASA Technical Reports Server (NTRS)
Kwak, Dochan
This viewgraph presentation gives an overview of viscous incompressible flow computations for three-dimensional steady and unsteady flows. Details are given on the use of computational fluid dynamics (CFD) as an engineering tool, solution methods for incompressible Navier-Stokes equations, numerical and physical characteristics of the primitive variable approach, and the role of CFD in the past and in current engineering and research applications.
Two dimensional MRT LB model for compressible and incompressible flows
Feng Chen; Aiguo Xu; Guangcai Zhang; Yonglong Wang
In the paper we extend the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett. \\textbf{90}, 54003 (2010)] so that it is suitable also for incompressible flows. To decrease the artificial oscillations, the convection term is discretized by the flux limiter scheme with splitting technique. New model is validated by some well-known benchmark tests, including Riemann problem and Couette flow, and satisfying agreements are obtained between the simulation results and analytical ones. In order to show the merit of LB model over traditional methods, the non-equilibrium characteristics of system are solved. The simulation results are consistent with physical analysis.
Weighted-mean scheme for solving incompressible viscous flow
NASA Technical Reports Server (NTRS)
Huynh, Q. Q.
The problem of how a boundary layer responds to the motion of a convexed vortex on a porous wall was investigated. The wall velocity is approximately given by Darcy's law. The vorticity-stream function approach was adopted for solving Navier-Stokes equations of two dimensional incompressible viscous flows. The weighted-mean scheme was used for constructing finite difference approximations of spatial derivatives. Several test problems were solved and numerical results demonstrate clearly the accuracy, stability, and efficiency of the scheme. The weighted mean scheme then can be applied to the vortical flow problem.
Laminar flow transition: A large-eddy simulation approach
NASA Technical Reports Server (NTRS)
Biringen, S.
A vectorized, semi-implicit code was developed for the solution of the time-dependent, three dimensional equations of motion in plane Poiseuille flow by the large-eddy simulation technique. The code is tested by comparing results with those obtained from the solutions of the Orr-Sommerfeld equation. Comparisons indicate that finite-differences employed along the cross-stream direction act as an implicit filter. This removes the necessity of explicit filtering along this direction (where a nonhomogeneous mesh is used) for the simulation of laminar flow transition into turbulence in which small scale turbulence will be accounted for by a subgrid scale turbulence model.
Viscous incompressible flow simulation using penalty finite element method
NASA Astrophysics Data System (ADS)
Sharma, R. L.
Numerical analysis of Navier-Stokes equations in velocity- pressure variables with traction boundary conditions for isothermal incompressible flow is presented. Specific to this study is formulation of boundary conditions on synthetic boundary characterized by traction due to friction and surface tension. The traction and open boundary conditions have been investigated in detail. Navier-Stokes equations are discretized in time using Crank-Nicolson scheme and in space using Galerkin finite element method. Pressure being unknown and is decoupled from the computations. It is determined as post processing of the velocity field. The justification to simulate this class of flow problems is presented through benchmark tests - classical lid-driven cavity flowwidely used by numerous authors due to its simple geometry and complicated flow behavior and squeezed flow between two parallel plates amenable to analytical solution. Results are presented for very low to high Reynolds numbers and compared with the benchmark results.
A correction function method to solve incompressible fluid flows to high accuracy with immersed geometries
Marques, Alexandre Noll
Numerical simulations of incompressible viscous flows in realistic configurations are increasingly important in many scientific and engineering fields. In Aeronautics, for instance, relatively cheap numerical computations ...
Passive tracer patchiness and particle trajectory stability in incompressible two-dimensional flows
Olascoaga, Maria Josefina
Passive tracer patchiness and particle trajectory stability in incompressible two-dimensional flows patchiness and particle trajectory stability in incompressible two-dimensional flows Francisco J. Beron and demonstrated numerically that particle trajectory stability is largely controlled by the background flow
A boundary element method for steady incompressible thermoviscous flow
NASA Technical Reports Server (NTRS)
Dargush, G. F.; Banerjee, P. K.
A boundary element formulation is presented for moderate Reynolds number, steady, incompressible, thermoviscous flows. The governing integral equations are written exclusively in terms of velocities and temperatures, thus eliminating the need for the computation of any gradients. Furthermore, with the introduction of reference velocities and temperatures, volume modeling can often be confined to only a small portion of the problem domain, typically near obstacles or walls. The numerical implementation includes higher order elements, adaptive integration and multiregion capability. Both the integral formulation and implementation are discussed in detail. Several examples illustrate the high level of accuracy that is obtainable with the current method.
A Fractional-Step Method Of Computing Incompressible Flow
NASA Technical Reports Server (NTRS)
Kwak, Dochan; Rosenfeld, Moshe; Vinokur, Marcel
Method of computing time-dependent flow of incompressible, viscous fluid involves numerical solution of Navier-Stokes equations on two- or three-dimensional computational grid based on generalized curvilinear coordinates. Equations of method derived in primitive-variable formulation. Dependent variables are pressure at center of each cell of computational grid and volume fluxes across faces of each cell. Volume fluxes replace Cartesian components of velocity; these fluxes correspond to contravariant components of velocity multiplied by volume of computational cell, in staggered grid. Choice of dependent variables enables simple extension of previously developed staggered-grid approach to generalized curvilinear coordinates and facilitates enforcement of conservation of mass.
New discretization and solution techniques for incompressible viscous flow problems
NASA Technical Reports Server (NTRS)
Gunzburger, M. D.; Nicolaides, R. A.; Liu, C. H.
Several topics arising in the finite element solution of the incompressible Navier-Stokes equations are considered. Specifically, the question of choosing finite element velocity/pressure spaces is addressed, particularly from the viewpoint of achieving stable discretizations leading to convergent pressure approximations. The role of artificial viscosity in viscous flow calculations is studied, emphasizing work by several researchers for the anisotropic case. The last section treats the problem of solving the nonlinear systems of equations which arise from the discretization. Time marching methods and classical iterative techniques, as well as some modifications are mentioned.
Pseudo-compressibility methods for the incompressible flow equations
NASA Technical Reports Server (NTRS)
Turkel, Eli; Arnone, A.
Preconditioning methods to accelerate convergence to a steady state for the incompressible fluid dynamics equations are considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Thus the steady state of the preconditioned system is the same as the steady state of the original system. The method is compared to other types of pseudo-compressibility. For finite difference methods preconditioning can change and improve the steady state solutions. An application to viscous flow around a cascade with a non-periodic mesh is presented.
Flow Solver for Incompressible 2-D Drive Cavity
NASA Technical Reports Server (NTRS)
Kalb, Virginia L.
This software solves the Navier-Stokes equations for the incompressible driven cavity flow problem. The code uses second-order finite differencing on a staggered grid using the Chorin projection method. The resulting intermediate Poisson equation is efficiently solved using the fast Fourier transform. Time stepping is done using fourth-order Runge-Kutta for stability at high Reynolds numbers. Features include check-pointing, periodic field snapshots, ongoing reporting of kinetic energy and changes between time steps, time histories at selected points, and optional streakline generation.
Error estimation and anisotropic mesh refinement for 3d laminar aerodynamic flow simulations
Hartmann, Ralf
Error estimation and anisotropic mesh refinement for 3d laminar aerodynamic flow simulations Tobias Leichta,b , Ralf Hartmann,a,b aInstitute of Aerodynamics and Flow Technology, DLR (German Aerospace Center-dimensional laminar aerodynamic flow simulations. The optimal order symmetric interior penalty discontinuous Galerkin
Manufacturing tolerances for natural laminar flow airframe surfaces
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Martin, G. L.; Domack, C. S.
Published aircraft surface waviness and boundary layer transition measurements imply that currently achievable low levels of surface waviness are compatible with the natural laminar flow (NLF) requirements of business and commuter aircraft, in the cases of both metallic and composite material airframes. The primary challenge to the manufacture of NLF-compatible surfaces is two-dimensional roughness in the form of steps and gaps at structural joints. Attention is presently given to recent NASA investigations of manufacturing tolerance requirements for NLF surfaces, including flight experiment results.
Laminar flow control leading edge systems in simulated airline service
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.
The feasibility of two candidate leading-edge flow laminarization systems applicable to airline service was tested using representative airline operational conditions with respect to air traffic, weather, and airport insect infestation. One of the systems involved a perforated Ti alloy suction surface with about 1 million 0.0025-in. diameter holes drilled by electron beam, as well as a Krueger-type flap that offered protective shielding against insect impingement; the other supplied surface suction through a slotted Ti alloy skin with 27 spanwise slots on the upper and lower surface.
Computation of incompressible viscous flows through turbopump components
NASA Technical Reports Server (NTRS)
Kiris, Cetin; Kwak, Dochan; Rogers, Stuart
A finite-difference, three-dimensional, incompressible Navier-Stokes formulation for calculating the flow through turbopump components is presented. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line-relaxation method. Both steady and unsteady flow calculations can be performed using the presented algorithm. In this paper, the equations are solved in steadily rotating reference frames by using the steady-state formulation in order to simulate the flow through a turbopump inducer. Eddy viscosity is computed by using the Baldwin-Lomax model. Numerical results are compared with experimental measurements and good agreement is found between the two. Time-accurate calculations will be reported in future publications.
Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow
NASA Astrophysics Data System (ADS)
Powell, Robert; Jenkins, Thomas
Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow. Robert L. Powell, Thomas P. Jenkins Department of Chemical Engineering & Materials Science University of California, Davis, CA 95616 Using laser Doppler velocimetry, we have measured the axial velocity profiles for steady, pressure driven, laminar flow of water in a circular tube. The flow was established in a one inch diameter seamless glass tube. The entry length prior to the measuring section was over one hundred diameters. Reynolds numbers in the range 500-2000 were used. Under conditions where the temperature difference between the fluid and the surroundings differed by as little as 0.2C, we found significant asymmetries in the velocity profiles. This asymmetry was most pronounced in the vertical plane. Varying the temperature difference moved the velocity maximum either above or below the centerline depending upon whether the fluid was warmer or cooler than the room. These results compare well to existing calculations. Using the available theory and our experiments it is possible to identify parameter ranges where non-ideal conditions(not parabolic velocity profiles) will be found. Supported by the EMSP Program of DOE.
Influence of coal properties on forward combustion in laminar flow
Lockwood, W.R.; Corlett, W.R.; Mortazaui, H.R.; Emery, A.F.
Numerical results are presented for forward combustion in coal channels wherein the flow is laminar. The work is motivated by the need to describe deviations from ideal permeative flow characteristics in theoretical models of underground rubble gasification. For simplicity, the geometry is idealized to a straight circular channel of initially uniform diameter. Coal and inlet gas properties, as well as gas flow rate and initial channel diameter, are arbitrary. A baseline case, in which O/sub 2/-steam is injected into a channel in virgin coal, is chosen to match laboratory work reported by other investigators. The results of independent variation of six major parameters are also shown. Finally, representative results are presented for injection of a hot mixture of steam and gasification products into hot char.
A viscous instability in axially symmetric laminar shear flows
NASA Astrophysics Data System (ADS)
Shakura, N.; Postnov, K.
A viscous instability in shearing laminar axisymmetric hydrodynamic flows around a gravitating centre is described. In the linearized hydrodynamic equations written in the Boussinesq approximation with microscopic molecular transport coefficients, the instability arises when the viscous dissipation is taken into account in the energy equation. Using the local WKB approximation, we derive a third-order algebraic dispersion equation with two modes representing the modified Rayleigh modes R+ and R-, and the third X-mode. We show that in thin accretion flows the viscosity destabilizes one of the Rayleigh modes in a wide range of wavenumbers, while the X-mode always remains stable. In Keplerian flows, the instability increment is found to be a few Keplerian rotational periods at wavelengths with kr ś 10-50. This instability may cause turbulence in astrophysical accretion discs even in the absence of magnetic field.
Longitudinal curvature and displacement speed effects on incompressible laminar boundary layers.
NASA Technical Reports Server (NTRS)
Werle, M. J.; Wornom, S. F.
The title problem is considered for the case of flow past a circular cylinder placed normal to a uniform mainstream with Reynolds numbers from 40 to 200. Implicit finite difference numerical solutions are obtained for a set of boundary-layer equations that account for the second order effects associated with surface curvature and displacement speed. It was found that both of these contributors have a significant influence on the internal structure of the viscous region and that an accurate estimate of the surface pressure distribution is essential for estimating the surface shear stress.
Feedback control of singular systems with applications to incompressible flows
NASA Astrophysics Data System (ADS)
Gandikota, Ramakrishna V.
Singular systems of differential equations, also referred to as differential algebraic equation (DAE) systems, arise as models in a variety of engineering applications. In chemical engineering, they typically arise under the quasi-steady state assumptions of phase, reaction or thermal equilibrium in the modeling of processes with fast mass transfer, reaction or heat transfer. They also arise in incompressible fluid flow systems. The control of singular systems has attracted considerable attention in the last two decades. The majority of the developed methods are on the state feedback control of linear and nonlinear singular systems in continuous-time, and they rely on the derivation of standard state space realizations (i.e. ODE descriptions) that can be used as the basis for the controller design. This thesis addresses (i) the derivation of state space realizations for the output feedback control of linear singular systems in continuous time, (ii) the derivation of state space realizations of singular systems of difference equations, which can be used for the state feedback control of nonlinear discrete time singular systems, (iii) a parallel analysis of the continuous in space and discretized in space incompressible Navier Stokes equations, with emphasis on the derivation of standard PDE and ODE descriptions respectively, and (iv) a case study on the numerical simulation and feedback control of the flow pattern in a lid-driven cavity. The performance of the developed controllers is illustrated via numerical simulation studies.
A SIMPLE based discontinuous Galerkin solver for steady incompressible flows
NASA Astrophysics Data System (ADS)
Klein, Benedikt; Kummer, Florian; Oberlack, Martin
In this paper we present how the well-known SIMPLE algorithm can be extended to solve the steady incompressible Navier-Stokes equations discretized by the discontinuous Galerkin method. The convective part is discretized by the local Lax-Friedrichs fluxes and the viscous part by the symmetric interior penalty method. Within the SIMPLE algorithm, the equations are solved in an iterative process. The discretized equations are linearized and an equation for the pressure is derived on the discrete level. The equations obtained for each velocity component and the pressure are decoupled and therefore can be solved sequentially, leading to an efficient solution procedure. The extension of the proposed scheme to the unsteady case is straightforward, where fully implicit time schemes can be used. Various test cases are carried out: the Poiseuille flow, the channel flow with constant transpiration, the Kovasznay flow, the flow into a corner and the backward-facing step flow. Using a mixed-order formulation, i.e. order k for the velocity and order k-1 for the pressure, the scheme is numerically stable for all test cases. Convergence rates of k+1 and k in the L2-norm are observed for velocity and pressure, respectively. A study of the convergence behavior of the SIMPLE algorithm shows that no under-relaxation for the pressure is needed, which is in strong contrast to the application of the SIMPLE algorithm in the context of the finite volume method or the continuous finite element method. We conclude that the proposed scheme is efficient to solve the steady incompressible Navier-Stokes equations in the context of the discontinuous Galerkin method comprising hp-accuracy.
A Note on the Wave Action Density of a Viscous Instability Mode on a Laminar Free-shear Flow
NASA Technical Reports Server (NTRS)
Balsa, Thomas F.
Using the assumptions of an incompressible and viscous flow at large Reynolds number, we derive the evolution equation for the wave action density of an instability wave traveling on top of a laminar free-shear flow. The instability is considered to be viscous; the purpose of the present work is to include the cumulative effect of the (locally) small viscous correction to the wave, over length and time scales on which the underlying base flow appears inhomogeneous owing to its viscous diffusion. As such, we generalize our previous work for inviscid waves. This generalization appears as an additional (but usually non-negligible) term in the equation for the wave action. The basic structure of the equation remains unaltered.
Analysis of laminar flow over a backward facing step; Proceedings of the Workshop, Bievres, France, January 18, 19, 1983
NASA Astrophysics Data System (ADS)
Morgan, K.; Periaux, J.; Thomasset, F.
Various numerical and experimental techniques being applied to solving the incompressible Navier-Stokes equations for flow over a backward facing step are discussed. Oil flows monitored with laser Doppler velocimetry are described, as are finite element and finite difference methods for discretized laminar flows. A quasi-linear finite element method, a nonlinear least squares method and an alternating direction technique are presented. Attention is also given to divergence-free quadrilateral elements and triangular elements, as well as to the effects on accuracy and computer run-time of increasing the number of grid points. An algorithm is described for decomposing the biharmonic equation into a finite number of Dirichlet problems for application to the Navier-Stokes equations.
Low temperature high current ion beams and laminar flows
NASA Astrophysics Data System (ADS)
Cavenago, Marco
Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x - px phase space area, for a beam with non uniform velocities. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.
Preprint of the paper "On the resolution of the viscous incompressible flow for various SUPG finite
Colominas, Ignasi
Preprint of the paper "On the resolution of the viscous incompressible flow for various SUPG finite-14 September 2000 ® ECCOMAS ON THE RESOLUTION OF THE VISCOUS INCOMPRESSIBLE FLOW FOR VARIOUS SUPG FINITE Stokes, SUPG. Abstract. A Finite Element based program has been released to solve the steady 2D Navier
Vortex solutions of the generalized Beltrami flows to the incompressible Euler equations
Fujimoto, Minoru; Yanase, Shinichiro
As for the solutions of the generalized Beltrami flows to the incompressible Euler equations besides the solutions separating radius and axial components, there are only several solutions found as the Hill's vortex solutions. We will present a series of vortex solutions in this category for the generalized Beltrami flows to the incompressible Euler equations.
A surface integral numerical solution for laminar developed duct flow
NASA Astrophysics Data System (ADS)
Khader, M. S.
A surface integral numerical solution for laminar developed flow in ducts of arbitrary shape cross sections is presented. The method is general for any two-dimensional duct with simple or multiple connected regions cross section. The solutions provide information for velocity distribution, friction factor, and wall shear stress. As an application of the present method, solutions for flow in circular and rectangular ducts are obtained. These solutions are used to compare the obtained results and the corresponding exact analytical solutions. Moreover, in order to illustrate the general use of the present scheme, a solution for the case of circular duct containing rod clusters is obtained. The method proved to have several interesting features and advantages over other conventional numerical and analytical techniques.
Laminar boundary-layer flow of non-Newtonian fluid
NASA Technical Reports Server (NTRS)
Lin, F. N.; Chern, S. Y.
A solution for the two-dimensional and axisymmetric laminar boundary-layer momentum equation of power-law non-Newtonian fluid is presented. The analysis makes use of the Merk-Chao series solution method originally devised for the flow of Newtonian fluid. The universal functions for the leading term in the series are tabulated for n from 0.2 to 2. Equations governing the universal functions associated with the second and the third terms are provided. The solution together with either Lighthill's formula or Chao's formula constitutes a simple yet general procedure for the calculation of wall shear and surface heat transfer rate. The theory was applied to flows over a circular cylinder and a sphere and the results compared with published data.
Unsteady laminar flow and convective heat transfer in a sharp 180 bend
Chung, Yongmann M.
Unsteady laminar flow and convective heat transfer in a sharp 180░ bend Yongmann M. Chung a , Paul Unsteady laminar flow and heat transfer in a sharp 180░ bend is studied numerically to investigate a convective heat transfer regime of especial relevance to electronic systems. Due to the high geometrical
Numerical solution of the Navier-Stokes equations for laminar, transonic flows
L. Turner III
An implicit finite difference solution of the Navier-Stokes equations yielded time histories of the transonic laminar flow development about a circular cylinder and NACA-0018 airfoil. Reynolds numbers ranged from those corresponding to purely laminar flow to those corresponding to significant turbulence in the boundary layer. Body thermal conditions of an adiabatic wall and a specified body temperature were considered. Versatility
AIR-BREATHING LAMINAR FLOW BASED MICROFLUIDIC FUEL CELL Ranga S. Jayashree1
Kenis, Paul J. A.
AIR-BREATHING LAMINAR FLOW BASED MICROFLUIDIC FUEL CELL Ranga S. Jayashree1 , Lajos Gancs2 , Eric R and solvents were purchased from the vendors indicated below. In addition, formic acid was obtained from Acros of the laminar flow-based microfluidic fuel cell. A 5-mm thick graphite plate (anode, fuel cell grade graphite
Distinct large-scale turbulent-laminar states in transitional pipe flow
Barkley, Dwight
Distinct large-scale turbulent-laminar states in transitional pipe flow David Moxey1 and Dwight) When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transi
Aerodynamic design of a natural laminar flow nacelle and the design validation by flight testing
H. Riedel; K.-H. Horstmann; A. Ronzheimer; M. Sitzmann
The laminar flow technology is one of the key technologies in aeronautics offering substantial improvements in the areas of economy and ecology. This paper describes the aerodynamic design methodology for a natural laminar flow (NLF) nacelle and the subsequent verification of the design quality by flight tests with a subsonic transport aircraft. The aerodynamic design was a contribution within the
Optimal product distribution from laminar flow reactors: Newtonian and other power-law fluids
Keith L. Levien; Octave Levenspiel
In tubular reactors viscous fluids are in laminar flow. For reactions in series this gives a product distribution different from either plug flow or mixed flow. More importantly, laminar flow depresses the maximum amount of intermediate that can be obtained when compared to plug flow. Here we treat the simple case of an elementary two-step mechanism:(1)[A?R?S]Three special cases of the
Transition-Sensitized Turbulence Models for Compressible and Incompressible Flows
NASA Technical Reports Server (NTRS)
Thacker, William D.
During the grant period from January 1,2002 to December 31,2002 work was carried out on three projects to extend the range of applicability of advanced turbulence models. First, a new transition-sensitized turbulence model was tested and refined. Second, the influence of compressibility on the pressure-strain rate correlation was studied. Third, the relationship between time-filtered large eddy simulation (TLES) and Reynolds-averaged Navier Stokes (RANS) modeling was investigated leading to submission of the article. The transition-sensitized turbulence model encompasses the early-stage transition and turbulent flow regimes describing the evolution of the ensemble mean disturbance energy and dissipation rate. It is founded on a consistent mathematical description of the laminar regime with its linear disturbances and the fully turbulent regime with its stochastic fluctuations. The unified description is provided by the ensemble viewpoint.
Lift-to-drag ratio and laminar flow control of a morphing laminar wing in a wind tunnel
Daniel Coutu; Vladimir Brailovski; Patrick Terriault; Mahmoud Mamou; Youssef Mķbarki; ╔ric Laurendeau
A new hardware-in-the-loop control strategy to enhance the aerodynamic performance of a two-dimensional morphing laminar wing prototype was developed and tested. The testing was performed in a wind tunnel under cruise flight flow conditions: Mach number ranging from 0.2 to 0.3 and angle of attack from - 1░ to 0.5░. For each set of flow conditions, the shape of the
An investigation of surfactant and enzyme formulations for the alleviation of insect contamination on Hybrid Laminar Flow Control (HLFC) surfaces
D O'Donoghue; T. M Young; J. T Pembroke; T. F O'Dwyer
Hybrid Laminar Flow Control (HLFC) is an active drag reduction technique that requires a small amount of air to be sucked through a porous skin surface, thus stabilising the boundary layer and permitting extended laminar flow along the wing surface. Contamination of the laminar flow surfaces by insects is a major concern for this technology. An overview of insect contamination
Incompressible Navier-Stokes calculations in pump flows
NASA Astrophysics Data System (ADS)
Kiris, Cetin; Chang, Leon; Kwak, Dochan
Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.
Postfragmentation density function for bacterial aggregates in laminar flow
NASA Astrophysics Data System (ADS)
Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John
The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation.
Computational wing design studies relating to natural laminar flow
NASA Technical Reports Server (NTRS)
Waggoner, Edgar G.
Two research studies are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wing planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first study supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. A wing was designed computationally for a corporate transport aircraft in the second study. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs.
Laminar flow around corners triggers the formation of biofilm streamers.
Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard A
Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments. PMID:20356880
M. Fiebig; U. Brockmeier; N. K. Mitra; T. G³ termann
Laminar velocity and temperature fields in a rectangular channel with a row of built-in vortex generators in the form of slender delta wings and winglet pairs have been calculated by means of a ifinal method consisting of zones of complete and partially parabolized Navier-Stokes and energy equations. A modified version of SOLA for incompressible as well as for variable-density, small-Mach
Predictions and observations of the flow field induced by laminar flow control microperforations
David G. MacManus; John A. Eaton
Hybrid laminar flow control (HLFC) aims to reduce aircraft skin friction drag by controlling the boundary-layer characteristics through a combination of surface suction and surface profile shaping. Suction is applied through an array of microperforations in the surface; and, to enable HLFC design criteria to be established with confidence, a full understanding of how these suction perforations affect the boundary
The effect of mako sharkskin on laminar flow separation
NASA Astrophysics Data System (ADS)
Bradshaw, Michael; Lang, Amy; Motta, Philip; Habegger, Maria; Hueter, Robert
Many animals possess effective performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (Isurus oxyrinchus). The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in flexibility over the body. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin as well as on various sections of the body. It is believed that the scale bristling may provide a mechanism for flow separation control that leads to decreased drag and increased maneuverability. This study involved testing a left pectoral fin of a shortfin mako shark as well as a cylinder with a sharkskin specimen applied circumferentially in a water tunnel facility under static, laminar conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the surfaces. Various Reynolds numbers were tested for both configurations, as well as several AOAs for the pectoral fin. The flow over the fin and cylinder were compared to a painted fin and a smooth PVC cylinder, respectively. The study found that the shark scales do, in fact, help to control flow separation. However, in order for the scales to bristle and trap the reversing flow, a certain magnitude of reversed flow and shear is required. This phenomenon seems to be most effective at near stall conditions and at higher Reynolds numbers. Many animals possess effective performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (Isurus oxyrinchus). The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in flexibility over the body. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin as well as on various sections of the body. It is believed that the scale bristling may provide a mechanism for flow separation control that leads to decreased drag and increased maneuverability. This study involved testing a left pectoral fin of a shortfin mako shark as well as a cylinder with a sharkskin specimen applied circumferentially in a water tunnel facility under static, laminar conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the surfaces. Various Reynolds numbers were tested for both configurations, as well as several AOAs for the pectoral fin. The flow over the fin and cylinder were compared to a painted fin and a smooth PVC cylinder, respectively. The study found that the shark scales do, in fact, help to control flow separation. However, in order for the scales to bristle and trap the reversing flow, a certain magnitude of reversed flow and shear is required. This phenomenon seems to be most effective at near stall conditions and at higher Reynolds numbers. Support from REU grant 1062611 is greatfully acknowledged.
Measurements of laminar and turbulent flow in a curved duct with thin inlet boundary layers
NASA Technical Reports Server (NTRS)
Taylor, A. M. K. P.; Whitelaw, J. H.; Yianneskis, M.
Laser Doppler velocimetry was used to measure the laminar and turbulent flow in a 90 deg square bend of strong curvature. The boundary layers at the inlet to the bend were approximately 25 percent and 15 percent of the hydraulic diameter for the laminar and turbulent flows, respectively. The development of the pressure driven secondary motion is more rapid for laminar flow: the maximum cross stream component measured was 60 percent of the bulk velocity in contrast to 40 percent for turbulent flow. The streamwise isotachs show that, for laminar flow, large velocities are found progressively nearer to the outer radius of the bend and along the sidewalls. For turbulent flow, the isotachs move towards the inner radius until about 60 deg around the bend where strong secondary motion results in a similar redistribution. Turbulence level and shear stress measurements are also presented.
Finite Element Simulation of Two-Dimensional Incompressible Magnetohydrodynamic Flows
NASA Astrophysics Data System (ADS)
Ip, Justin Tsz Ching
A new finite element code has been developed for simulation of the dynamics of two-dimensional incompressible magnetohydrodynamic flows. The solution scheme used in spatial discretization is the Galerkin weighted-residual finite-element method, incorporating the mixed interpolation technique, and a combination of the penalty and pseudocompressibility methods for implementing the incompressibility constraint. An implicit and stable theta-weighting finite difference scheme is used for integration in time, and a non-iterative time-level averaging method is employed for treatment of nonlinear terms. The code has been extensively benchmarked against known analytical solutions in magnetohydrodynamics and has been found to produce highly accurate results. The tearing-mode instability of a magnetic-field-reversing current sheet in the presence of coplanar stagnation-point flow, in which the unperturbed equilibrium state is an exact solution of the steady-state dissipative MHD equations, has been examined by use of the code. Simulation results indicate stability for sufficiently small values of the viscous Lundquist number, S_nu, or the resistive Lundquist number, S_eta : a curve in the S_nu -S_eta plane separating the stable and unstable regions has been found. In the unstable regime, the results show occurrence of multiple x-line reconnection along the center of the current sheet at x = 0. Small-scale structures of vorticity and current density near the x-point reconnection sites are observed and are found to be consistent with results obtained by Matthaeus (1982). Average linear growth rates are estimated for modest values of S_eta. In the range S_eta<=500, the number of magnetic islands is found to be independent of Seta, which implies that there exists a single dominant wavelength of the tearing-mode in this range. The stretching of magnetic islands which is present in this configuration but not in the perpendicular flow and field configuration examined by Phan and Sonnerup (1991), caused a substantial decrease in linear growth rate relative to that obtained by those authors. It is of particular interest that, unlike most simulations of the tearing-mode, no symmetry conditions are imposed on the perturbations; nevertheless they develop in an anti -symmetric manner.
Calculation of laminar and turbulent boundary layers for two-dimensional time-dependent flows
NASA Technical Reports Server (NTRS)
Cebeci, T.
A general method for computing laminar and turbulent boundary layers for two-dimensional time-dependent flows is presented. The method uses an eddy-viscosity formulation to model the Reynolds shear-stress term and a very efficient numerical method to solve the governing equations. The model was applied to steady two-dimensional and three-dimensional flows and was shown to give good results. A discussion of the numerical method and the results obtained by the present method for both laminar and turbulent flows are discussed. Based on these results, the method is efficient and suitable for solving time-dependent laminar and turbulent boundary layers.
A new expicit projection method for incompressible flows
NASA Astrophysics Data System (ADS)
Park, Sangro; Lee, Changhoon
When solving unsteady incompressible flows, the divergence-free condition should be satisfied. For this, the non-linear terms in the Navier-Stokes equation should be projected onto divergence-free space by an operator which arises from taking divergence of the Navier-Stokes equation. The calculation of projecting non-linear fields requires a lot of computational cost because the projection typically relies on an iterative solution of pressure. In this study, we propose an explicit projection method based on the spectral solution of the Poisson equation in the infinite domain and local truncation in the physical space, which does not require iterations. For validations of our methods, we applied the proposed method to the 2-dimensional Taylor-Green vortex simulation and forced isotropic turbulence simulation. The test results show that our method saved computational cost enormously while maintaining reasonable accuracy of flow field. More details about the suggested method and the performance of the method will be discussed in the meeting.
Theoretical analysis of incompressible flow through a radial-inlet centrifugal impeller at various weight flows
NASA Technical Reports Server (NTRS)
Kramer, James J; Prian, Vasily D; Wu, Chung-Hua
A method for the solution of the incompressible nonviscous flow through a centrifugal impeller, including the inlet region, is presented. Several numerical solutions are obtained for four weight flows through an impeller at one operating speed. These solutions are refined in the leading-edge region. The results are presented in a series of figures showing streamlines and relative velocity contours. A comparison is made with the results obtained by using a rapid approximate method of analysis.
Thermal Behavior of Laminar Periodic Channel Flow over Triangular Baffles
NASA Astrophysics Data System (ADS)
Nivesrangsan, P.; Sripattanapipat, S.; Eiamsa-ard, S.; Promvonge, P.
Laminar periodic flow and heat transfer in a two dimensional horizontal channel with isothermal walls and with staggered triangular baffles are numerically investigated. The computations are based on the finite volume method, and the SIMPLE algorithm with QUICK scheme is implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 100 to 600. Effects of different baffle tip angles on heat transfer and pressure loss in the channel are studied and the results of the triangular baffle are also compared with those of the flat baffle. It is observed that apart from the rise of Reynolds number, the reduction of the baffle tip angle leads to an increase in the Nusselt number and friction factor. According to the computational results for triangular baffles, the optimum thermal performance is found at the baffle angle of 5░, baffle height to channel height ratio of 0.5 and baffle spacing to channel height ratio of 1.0. In addition, the thermal performances of the 5░-10░ triangular baffles are found to be higher than that of the flat baffle for all Reynolds numbers used.
Velocity fluctuations and energy amplification in laminar fluid flows
NASA Astrophysics Data System (ADS)
Ortiz de Zarate, Jose M.; Sengers, Jan V.
We present a systematic procedure for evaluating the intrinsic velocity fluctuations and the resulting intrinsic energy amplification that are always present in laminar fluid flows. For this purpose we formulate a stochastic Orr-Sommerfeld equation and a stochastic Squire equation by applying a fluctuation-dissipation theorem for the random part of the dissipative stresses. From the solution of the stochastic Orr- Sommerfeld and Squire equations the intrinsic energy amplification can be deduced. As an illustration of the procedure we present an explicit solution for the case of planar Couette flow. We first solve the fluctuating hydrodynamics equations in the bulk, obtaining an exact representation of the spatial spectrum of the velocity fluctuations valid for large wave numbers. The resulting energy amplification is proportional to Re^3/2. Next, we show how to a good approximation confinement can be incorporated by a simple Galerkin projection technique. The effect of the boundary conditions is to reduce the energy amplification to a logarithmic dependence on Re. We shall also indicate how an exact solution for the case of confined geometries can be obtained by an expansion into a set of hydrodynamic modes, conveniently expressed in terms of Airy functions.
Erosion of a granular bed driven by laminar fluid flow
A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman
Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.
Accurate and robust methods for variable density incompressible flows with discontinuities
Rider, W.J.; Kothe, D.B.; Puckett, E.G.
We are interested in the solution of incompressible flows which are characterized by large density variations, interfacial physics, arbitrary material topologies and strong vortical content. The issues present in constant density incompressible flow are exacerbated by the presence of density discontinuities. A much greater premium requirement is placed the positivity of computed quantities The mechanism of baroclinc vorticity generation exists ({gradient}p x {gradient}p) to further complicate the physics.
3-D laser Doppler velocimetry study of incompressible flow through an orifice plate
Panak, David Leo
3-D LASER DOPPLER VELOCIMETRY STUDY OF INCOMPRESSIBLE FLOW THROUGH AN ORIFICE PLATE A Thesis by DAVID LEO PANAK Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE May 1990 Major Subject: Mechanical Engineering 3-D LASER DOPPLER VELOCIMETRY STUDY OF INCOMPRESSIBLE FLOW THROUGH AN ORIFICE PLATE A Thesis DAVID LEO PANAK Approved as to style and content by: Gerald Morriso (Chair of Commi ee...
The exact calculation of quadrupole sources for some incompressible flows
NASA Technical Reports Server (NTRS)
Brentner, Kenneth S.
This paper is concerned with the application of the acoustic analogy of Lighthill to the acoustic and aerodynamic problems associated with moving bodies. The Ffowcs Williams-Hawkings equation, which is an interpretation of the acoustic analogy for sound generation by moving bodies, manipulates the source terms into surface and volume sources. Quite often in practice the volume sources, or quadrupoles, are neglected for various reasons. Recently, Farassat, Long and others have attempted to use the FW-H equation with the quadrupole source and neglected to solve for the surface pressure on the body. The purpose of this paper is to examine the contribution of the quadrupole source to the acoustic pressure and body surface pressure for some problems for which the exact solution is known. The inviscid, incompressible, 2-D flow, calculated using the velocity potential, is used to calculate the individual contributions of the various surface and volume source terms in the FW-H equation. The relative importance of each of the sources is then assessed.
The exact calculation of quadrupole sources for some incompressible flows
NASA Astrophysics Data System (ADS)
Brentner, Kenneth S.
This paper is concerned with the application of the acoustic analogy of Lighthill to the acoustic and aerodynamic problems associated with moving bodies. The Ffowcs Williams-Hawkings equation, which is an interpretation of the acoustic analogy for sound generation by moving bodies, manipulates the source terms into surface and volume sources. Quite often in practice the volume sources, or quadrupoles, are neglected for various reasons. Recently, Farassat, Long and others have attempted to use the FW-H equation with the quadrupole source and neglected to solve for the surface pressure on the body. The purpose of this paper is to examine the contribution of the quadrupole source to the acoustic pressure and body surface pressure for some problems for which the exact solution is known. The inviscid, incompressible, 2-D flow, calculated using the velocity potential, is used to calculate the individual contributions of the various surface and volume source terms in the FW-H equation. The relative importance of each of the sources is then assessed.
A massively parallel fractional step solver for incompressible flows
NASA Astrophysics Data System (ADS)
Houzeaux, G.; Vßzquez, M.; Aubry, R.; Cela, J. M.
This paper presents a parallel implementation of fractional solvers for the incompressible Navier-Stokes equations using an algebraic approach. Under this framework, predictor-corrector and incremental projection schemes are seen as sub-classes of the same class, making apparent its differences and similarities. An additional advantage of this approach is to set a common basis for a parallelization strategy, which can be extended to other split techniques or to compressible flows. The predictor-corrector scheme consists in solving the momentum equation and a modified "continuity" equation (namely a simple iteration for the pressure Schur complement) consecutively in order to converge to the monolithic solution, thus avoiding fractional errors. On the other hand, the incremental projection scheme solves only one iteration of the predictor-corrector per time step and adds a correction equation to fulfill the mass conservation. As shown in the paper, these two schemes are very well suited for massively parallel implementation. In fact, when compared with monolithic schemes, simpler solvers and preconditioners can be used to solve the non-symmetric momentum equations (GMRES, Bi-CGSTAB) and to solve the symmetric continuity equation (CG, Deflated CG). This gives good speedup properties of the algorithm. The implementation of the mesh partitioning technique is presented, as well as the parallel performances and speedups for thousands of processors.
Natural laminar flow flight experiments on a turbine engine nacelle fairing
NASA Technical Reports Server (NTRS)
Obara, C. J.; Hastings, E. C.; Schoenster, J. A.; Parrott, T. L.; Holmes, B. J.
Flight experiments are being conducted with the objective to investigate the interactions between acoustic disturbances and laminar flow in the flight environment. In the experiments, the laminar boundary layer on the nacelles will be exposed to discrete and broadband external noises, and the effect of varying noise levels and frequencies on the stability of the laminar flow will be studied. The present paper provides an overview of the complete project and a status report on the results which have been obtained. The flight experiment is conducted with the aid of a modified research aircraft. The phase I flight tests are concerned with a quick and simple determination of natural laminar flow (NLF) behavior on an engine nacelle. Attention is given to instrumentation, the acoustic noise source, flow visualization, and the test results.
Design and operation of a laminar-flow electrostatic-quadrupole-focused acceleration column
Maschke, A.W.
This report deals with the design principles involved in the design of a laminar-flow electrostatic-quadrupole-focused acceleration column. In particular, attention will be paid to making the parameters suitable for incorporation into a DC MEQALAC design.
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong
This is the presentation related to the paper of the same name describing Reynolds Averaged Navier Stokes (RANS) computational Fluid Dynamics (CFD) analysis of low speed stall aerodynamics of a swept wing with a laminar flow wing glove.
Video- Demonstration of Laminar Flow in a Liquid Onboard the International Space Station (ISS)
NASA Technical Reports Server (NTRS)
Saturday Morning Science, the science of opportunity series of applied experiments and demonstrations, performed aboard the International Space Station (ISS) by Expedition 6 astronaut Dr. Don Pettit, revealed some remarkable findings. In this video clip, Pettit demonstrates laminar flow in a rotating film of water. The demonstration is done by placing tracer particles in a water film held in place by a round wire loop, then stirring the system rotationally. The resulting flow clearly demonstrates laminar 2D behavior with spiraling streamlines.
A preliminary design study on an acoustic muffler for the laminar flow transition research apparatus
NASA Technical Reports Server (NTRS)
Abrahamson, A. L.
An acoustic muffler design of a research tool for studying laminar flow and the mechanisms of transition, the Laminar Flow and Transition Research Apparatus (LFTRA) is investigated. Since the presence of acoustic pressure fluctuations is known to affect transition, low background noise levels in the test section of the LFTRA are mandatory. The difficulties and tradeoffs of various muffler design concepts are discussed and the most promising candidates are emphasized.
Distributed acoustic receptivity in laminar flow control configurations
NASA Technical Reports Server (NTRS)
Choudhari, Meelan
A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied, within the Orr-Sommerfield framework, by a suitable extension of the Goldstein-Ruban theory for receptivity due to localized disturbances on the airfoil surface. The results, thus, complement the earlier work on the receptivity produced by local variations in the surface suction and/or surface admittance. In particular, we show that the cumulative effect of the distributed receptivity can be substantially larger than that of a single, isolated suction strip or slot. Furthermore, even if the receptivity is spread out over very large distances, the most effective contributions come from a relatively short region in vicinity of the lower branch of the neutral stability curve. The length scale of this region is intermediate to that of the mean of these two length scales. Finally, it is found that the receptivity is effectively dominated by a narrow band of Fourier components from the wall-suction and admittance distributions, roughly corresponding to a detuning of less than ten percent with respect to the neutral instability wavenumber at the frequency under consideration. The results suggest that the drop-off in receptivity magnitudes away from the resonant wavenumber is nearly independent of the frequency parameter.
Frost Growth and Densification in Laminar Flow Over Flat Surfaces
NASA Technical Reports Server (NTRS)
Kandula, Max
One-dimensional frost growth and densification in laminar flow over flat surfaces has been theoretically investigated. Improved representations of frost density and effective thermal conductivity applicable to a wide range of frost circumstances have been incorporated. The validity of the proposed model considering heat and mass diffusion in the frost layer is tested by a comparison of the predictions with data from various investigators for frost parameters including frost thickness, frost surface temperature, frost density and heat flux. The test conditions cover a range of wall temperature, air humidity ratio, air velocity, and air temperature, and the effect of these variables on the frost parameters has been exemplified. Satisfactory agreement is achieved between the model predictions and the various test data considered. The prevailing uncertainties concerning the role air velocity and air temperature on frost development have been elucidated. It is concluded that that for flat surfaces increases in air velocity have no appreciable effect on frost thickness but contribute to significant frost densification, while increase in air temperatures results in a slight increase the frost thickness and appreciable frost densification.
Preconditioned solenoidal basis method for incompressible fluid flowsĀ
Wang, Xue
This thesis presents a preconditioned solenoidal basis method to solve the algebraic system arising from the linearization and discretization of primitive variable formulations of Navier-Stokes equations for incompressible ...
Observations and implications of natural laminar flow on practical airplane surfaces
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.
The results of natural laminar flow (NLF) experiments conducted by NASA to determine if modern aircraft structures can benefit from NLF as do sailplanes are presented. Seven aircraft, ranging from a Cessna 210 to a Learjet 28/29, with relatively stiff skins were flown in production configurations with no modifications. Measurements were made of the boundary-layer laminar to turbulent transition locations on various aerodynamic surfaces, the effect of a total loss of laminar flow, the effect of the propeller slipstream on the wing boundary-layer transition and the boundary-layer profiles, the wing section profile drag, the effect of flight through clouds, and insect debris contamination effects. Favorable pressure gradients for NLF were concluded to be feasible up to a transition Reynolds number of 11 million. Laminar flows were observed in propeller slipstreams, and insects were found to cause transition 1/4 of the time.
Bifurcation and stability analysis of laminar isothermal counterflowing jets
We present a numerical study of the structure and stability of laminar isothermal flows formed by two counterflowing jets of an incompressible Newtonian fluid. We demonstrate that symmetric counterflowing jets with identical mass flow rates exhibit multiple steady states and, in certain cases, time-dependent (periodic) steady states. Two geometric configurations were studied based on the inlet jet shapes: planar and
Lift-to-drag ratio and laminar flow control of a morphing laminar wing in a wind tunnel
NASA Astrophysics Data System (ADS)
Coutu, Daniel; Brailovski, Vladimir; Terriault, Patrick; Mamou, Mahmoud; Mķbarki, Youssef; Laurendeau, ╔ric
A new hardware-in-the-loop control strategy to enhance the aerodynamic performance of a two-dimensional morphing laminar wing prototype was developed and tested. The testing was performed in a wind tunnel under cruise flight flow conditions: Mach number ranging from 0.2 to 0.3 and angle of attack from - 1░ to 0.5░. For each set of flow conditions, the shape of the upper surface of the wing was modified using two independent shape memory alloy actuators. The wing shape was morphed in two sequential steps. The initial morphed shape was controlled using open-loop architecture and the results of an anterior aero-structural numerical optimization study. The final morphed shape was closed-loop controlled using either the wind tunnel balance or an infrared camera as hardware-in-the-loop to give an instantaneous lift-to-drag ratio (L/D) or a laminar flow extension (xtr/c) over the upper surface of the prototype. In respect to the aerodynamic performance of the unactuated wing profile, the L/D gain varies from 10.6 to 15% for the closed-loop control strategy compared to 10.0 to 13.7% for the open-loop control strategy. Laminar flow extension gains, ?xtr/c, measured by infrared camera, were situated in the 29-33% range for both control strategies. However, the results obtained showed that the closed-loop controller could be hindered by the noise of the hardware-in-the-loop signal.
Flow visualization of supersonic laminar flow over a backward-facing step via NPLS
NASA Astrophysics Data System (ADS)
Chen, Z.; Yi, S. H.; Tian, L. F.; He, L.; Zhu, Y. Z.
An experimental study on a supersonic laminar flow over a backward-facing step of 5 mm height was undertaken in a low-noise indraft wind tunnel. To investigate the fine structures of Ma = 3.0 and 3.8 laminar flow over a backward-facing step, nanotracer planar laser scattering was adopted for flow visualization. Flow structures, including supersonic laminar boundary layer, separation, reattachment, redeveloping turbulent boundary layer, expansion wave fan and reattachment shock, were revealed in the transient flow fields. In the Ma = 3.0 BFS (backward-facing step) flow, by measuring four typical regions, it could be found that the emergence of weak shock waves was related to the K-H (Kelvin-Helmholtz) vortex which appeared in the free shear layer and that the convergence of these waves into a reattachment shock was distinct. Based on large numbers of measurements, the structure of time-averaging flow field could be gained. Reattachment occurred at the location downstream from the step, about 7-7.5 h distance. After reattachment, the recovery boundary layer developed into turbulence quickly and its thickness increased at an angle of 4.6░. At the location of X = 14 h, the redeveloping boundary layer was about ten times thicker than its original thickness, but it still had not changed into fully developed turbulence. However, in the Ma = 3.8 flow, the emergence of weak shock waves could be seen seldom, due to the decrease of expansion. The reattachment point was thought to be near X = 15 h according to the averaging result. The reattachment shock was not legible, which meant the expansion and compression effects were not intensive.
Hybrid laminar flow control tests in the Boeing Research Wind Tunnel
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Lund, D. W.; George-Falvy, D.; Nagel, A. L.
The hybrid laminar flow control (HLFC) concept has undergone wind tunnel testing at near full-scale Reynolds number on an infinite wing of 30-deg sweep on which boundary-layer suction was furnished over the first 20 percent of chord of the upper surface. Depending on the external pressure distribution, the HLFC extended the laminarity of the boundary layer as far back as 45 percent of chord; this corresponds to a transition Reynolds number of about 11 million. The maximum chordwise extent of laminar run was found to be insensitive to the suction level over a wide range.
A computational model for the laminar flow boundary layer in a thermally driven vortex
E. S. Wilbarger Jr.
The model was developed using the method of finite differences. The complete, compressible form of the steady state Navier-Stokes equations, the continuity equation and energy equation were employed. A variable step size computational grid was used to conserve computer storage space. Laminar flows were computed for both rigid body outer flow and combined potential-rigid body core outer flow for isothermal
A conservative immersed interface method for Large-Eddy Simulation of incompressible flows
M. Meyer; A. Devesa; S. Hickel; X.Y. Hu; N.A. Adams
We propose a conservative, second-order accurate immersed interface method for representing incompressible fluid flows over complex three dimensional solid obstacles on a staggered Cartesian grid. The method is based on a finite-volume discretization of the incompressible Navier¢Stokes equations which is modified locally in cells that are cut by the interface in such a way that accuracy and conservativity are maintained.
F-15B in flight showing Supersonic Natural Laminar Flow (SS-NLF) experiment attached vertically to t
NASA Technical Reports Server (NTRS)
In-flight photo of the F-15B equipped with the Supersonic Natural Laminar Flow (SS-NLF) experiment. During four research flights, laminar flow was achieved over 80 percent of the test wing at speeds approaching Mach 2. This was accomplished as the sole result of the shape of the wing, without the use of suction gloves, such as on the F-16XL. Laminar flow is a condition in which air passes over a wing in smooth layers, rather than being turbulent The greater the area of laminar flow, the lower the amount of friction drag on the wing, thus increasing an aircraft's range and fuel economy. Increasing the area of laminar flow on a wing has been the subject of research by engineers since the late 1940s, but substantial success has proven elusive. The SS-NLF experiment was intended to provide engineers with the data by which to design natural laminar flow wings.
An efficient algorithm for incompressible N-phase flows
NASA Astrophysics Data System (ADS)
Dong, S.
We present an efficient algorithm within the phase field framework for simulating the motion of a mixture of N (N?2) immiscible incompressible fluids, with possibly very different physical properties such as densities, viscosities, and pairwise surface tensions. The algorithm employs a physical formulation for the N-phase system that honors the conservations of mass and momentum and the second law of thermodynamics. We present a method for uniquely determining the mixing energy density coefficients involved in the N-phase model based on the pairwise surface tensions among the N fluids. Our numerical algorithm has several attractive properties that make it computationally very efficient: (i) it has completely de-coupled the computations for different flow variables, and has also completely de-coupled the computations for the (N-1) phase field functions; (ii) the algorithm only requires the solution of linear algebraic systems after discretization, and no nonlinear algebraic solve is needed; (iii) for each flow variable the linear algebraic system involves only constant and time-independent coefficient matrices, which can be pre-computed during pre-processing, despite the variable density and variable viscosity of the N-phase mixture; (iv) within a time step the semi-discretized system involves only individual de-coupled Helmholtz-type (including Poisson) equations, despite the strongly-coupled phase-field system of fourth spatial order at the continuum level; (v) the algorithm is suitable for large density contrasts and large viscosity contrasts among the N fluids. Extensive numerical experiments have been presented for several problems involving multiple fluid phases, large density contrasts and large viscosity contrasts. In particular, we compare our simulations with the de Gennes theory, and demonstrate that our method produces physically accurate results for multiple fluid phases. We also demonstrate the significant and sometimes dramatic effects of the gravity, density ratios, pairwise surface tensions, and drop sizes on the N-phase configurations and dynamics. The numerical results show that the method developed herein is capable of dealing with N-phase systems with large density ratios, large viscosity ratios, and pairwise surface tensions, and that it can be a powerful tool for studying the interactions among multiple types of fluid interfaces.
An investigation of Newton-Krylov algorithms for solving incompressible and low Mach number compressible fluid flow and heat transfer problems using finite volume discretization
McHugh, P.R.
Fully coupled, Newton-Krylov algorithms are investigated for solving strongly coupled, nonlinear systems of partial differential equations arising in the field of computational fluid dynamics. Primitive variable forms of the steady incompressible and compressible Navier-Stokes and energy equations that describe the flow of a laminar Newtonian fluid in two-dimensions are specifically considered. Numerical solutions are obtained by first integrating over discrete finite volumes that compose the computational mesh. The resulting system of nonlinear algebraic equations are linearized using Newton`s method. Preconditioned Krylov subspace based iterative algorithms then solve these linear systems on each Newton iteration. Selected Krylov algorithms include the Arnoldi-based Generalized Minimal RESidual (GMRES) algorithm, and the Lanczos-based Conjugate Gradients Squared (CGS), Bi-CGSTAB, and Transpose-Free Quasi-Minimal Residual (TFQMR) algorithms. Both Incomplete Lower-Upper (ILU) factorization and domain-based additive and multiplicative Schwarz preconditioning strategies are studied. Numerical techniques such as mesh sequencing, adaptive damping, pseudo-transient relaxation, and parameter continuation are used to improve the solution efficiency, while algorithm implementation is simplified using a numerical Jacobian evaluation. The capabilities of standard Newton-Krylov algorithms are demonstrated via solutions to both incompressible and compressible flow problems. Incompressible flow problems include natural convection in an enclosed cavity, and mixed/forced convection past a backward facing step.
Numerical investigation of pressure drop and heat transfer in developing laminar and turbulent nanofluid flows
NASA Astrophysics Data System (ADS)
Ziaei-Rad, Masoud
This paper concerns the study of laminar and turbulent force convection heat transfer and pressure drop between horizontal parallel plates with a nanofluid composed of Al2O3 and water. A set of governing equations are solved using a non-staggered SIMPLE procedure for the velocity-pressure coupling. For the convection-diffusion terms a power-law scheme is employed. A modified k-? model with a two-layer technique for the near-wall region has been used to predict the turbulent viscosity. The effects of nanoparticle volume fraction in the base fluid on laminar and turbulent flow variables are presented and discussed. The velocity and temperature profiles, friction factor, pressure coefficient and Nusselt number at different Reynolds numbers in the entrance region for both the laminar and turbulent flow regimes are reported under different thermal boundary conditions. The results show that the effect of the presence of nanoparticles in the base fluid on hydraulic and thermal parameters for the turbulent flow is not very significant, while the rate of heat transfer for the laminar flow with nanoparticles is greater than that of the base liquid. Furthermore, the thermal boundary layer and consequently the Nusselt number more quickly reach their fully developed values by increasing the percentage of nanoparticles in the base fluid for the laminar flow regime, while no changes in the trend are observed for the turbulent flow.
Numerical methods for incompressible viscous flows with engineering applications
NASA Technical Reports Server (NTRS)
Rose, M. E.; Ash, R. L.
A numerical scheme has been developed to solve the incompressible, 3-D Navier-Stokes equations using velocity-vorticity variables. This report summarizes the development of the numerical approximation schemes for the divergence and curl of the velocity vector fields and the development of compact schemes for handling boundary and initial boundary value problems.
On the method of pseudo compressibility for numerically solving incompressible flows
NASA Technical Reports Server (NTRS)
Chang, J. L. C.; Kwak, D.
Pseudo compressibility is used for numerically solving incompressible flows to achieve computational efficiency. The use of pseudo compressibility results in a system of hyperbolic-type equations of motion that introduce waves of finite speed. The interactions of the wave propagation and the vorticity spreading are analyzed. A criterion governing the dependence of the pseudo compressiblity on the Reynolds number and the characteristic length of the flow geometry is obtained that allows for a proper convergence. It is demonstrated that the solution does tend to the incompressible limit. External and internal viscous flow test problems are presented to verify the theory.
Design of a laminar-flow-control supercritical airfoil for a swept wing
NASA Technical Reports Server (NTRS)
Allison, D. O.; Dagenhart, J. R.
An airfoil was analytically designed and analyzed for a combination of supercritical flow and laminar flow control (LFC) by boundary layer suction. A shockless inverse method was used to design an airfoil and an analysis method was used in lower surface redesign work. The laminar flow pressure distributions were computed without a boundary layer under the assumption that the laminar boundary layer would be kept thin by suction. Inviscid calculations showed that this 13.5 percent thick airfoil has shockless flows for conditions at and below the design normal Mach number of 0.73 and the design section lift coefficient of 0.60, and that the maximum local normal Mach number is 1.12 at the design point. The laminar boundary layer instabilities can be controlled with suction but the undercut leading edge of the airfoil provides a low velocity, constant pressure coefficients region which is conducive to laminar flow without suction. The airfoil was designed to be capable of lift recovery with no suction by the deflection of a small trailing edge flap.
Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport (HSCT). Boundary-layer transition data have been obtained on the titanium glove primarily at Mach 2.0 and altitudes of 53,000-55,000 ft. The objectives of this supersonic laminar flow control flight experiment have been to achieve 50- to 60-percent-chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point (Mach 1.9 at an altitude of 50,000 ft). At Mach 2.0 and an altitude of 53,000 ft, which corresponds to a Reynolds number of 22.7 X 10(exp 6), optimum suction levels have allowed long runs of a minimum of 46-percent-chord laminar flow to be achieved. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
A History of Suction-Type Laminar Flow Control with Emphasis on Flight Research
NASA Technical Reports Server (NTRS)
Braslow, Albert L.
Laminar-flow control is an area of aeronautical research that has a long history at NASA's Langley Research Center, Dryden Flight Research Center, their predecessor organizations, and elsewhere. In this monograph, the author, who spent much of his career at Langley working with this research, presents a history of that portion of laminar-flow technology known as active laminar-flow control, which employs suction of a small quantity of air through airplane surfaces. This important technique offers the potential for significant reduction in drag and, thereby, for large increases in range or reductions in fuel usage for aircraft. For transport aircraft, the reductions in fuel consumed as a result of laminar-flow control may equal 30 percent of present consumption. Given such potential, it is obvious that active laminar-flow control with suction is an important technology. In this study, the author covers the early history of the subject and brings the story all the way to the mid-1990s with an emphasis on flight research, much of which has occurred at Dryden. This is an important monograph that not only encapsulates a lot of history in a brief compass but also does so in language that is accessible to non-technical readers. NASA is publishing it in a format that will enable it to reach the wide audience the subject deserves.
Design and Experimental Results for a Natural-Laminar-Flow Airfoil for General Aviation Applications
NASA Technical Reports Server (NTRS)
Somers, D. M.
A natural-laminar-flow airfoil for general aviation applications, the NLF(1)-0416, was designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low-speed airfoils with the low cruise drag of the NACA 6-series airfoils was achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge was also met. Comparisons of the theoretical and experimental results show excellent agreement. Comparisons with other airfoils, both laminar flow and turbulent flow, confirm the achievement of the basic objective.
Measurement of fluid velocity development in laminar pipe flow using laser Doppler velocimetry
NASA Astrophysics Data System (ADS)
Molki, Arman; Khezzar, Lyes; Goharzadeh, Afshin
In this paper we present a non-intrusive experimental approach for obtaining velocity gradient profiles in a transparent smooth pipe under laminar flow conditions (Re = 925) using a laser Doppler velocimeter (LDV). Measurements were taken within the entrance region of the pipe at l = 300 mm and l = 600 mm from the pipe inlet, in addition to measurements of the fully developed flow at l = 1800 mm. The obtained results show how the velocity profile from upstream of the pipe develops into a classical laminar profile downstream, which matches the theoretical profile well. Additionally, a brief summary of historical information about the development of flow measurement techniques, in particular LDV, is provided.
Applications of stencil-adaptive finite difference method to incompressible viscous flows with curved boundary
H. Ding; C. Shu; Q. D. Cai
This paper investigates the applicability of the stencil-adaptive finite difference method for the simulation of two-dimensional unsteady incompressible viscous flows with curved boundary. The adaptive stencil refinement algorithm has been proven to be able to continuously adapt the stencil resolution according to the gradient of flow parameter of interest [Ding H, Shu C. A stencil adaptive algorithm for finite difference
A sufficient condition for the linear stability of magnetohydrodynamic equilibria with field aligned incompressible flows
Throumoulopoulos, G. N.; Tasso, H. [University of Ioannina, Association Euratom-Hellenic Republic, Division of Theoretical Physics, GR 451 10 Ioannina (Greece); Max-Planck-Institut fuer Plasmaphysik, Euratom Association, D-85748 Garching (Germany)
A sufficient condition for the linear stability of three dimensional equilibria with incompressible flows parallel to the magnetic field is derived. The condition refers to internal modes and involves physically interpretable terms related to the magnetic shear and the flow shear.
A front-tracking method for viscous, incompressible, multi-fluid flows
Salih O. Unverdi; Gretar Tryggvason
Attention is given to a method to simulate unsteady multifluid flows in which a sharp interface or a front separate incompressible fluids of different density and viscosity. The flow field is discretized by a conservative finite difference approximation on a stationary grid, and the interface is explicitly represented by a separate, unstructured grid that moves through the stationary grid. Since
A Study of Transition to Turbulence for Incompressible Pipe Flow using a
Patriksson, Michael
A Study of Transition to Turbulence for Incompressible Pipe Flow using a Spectral Finite Element and Reynolds. From his experiments on the stability of flow in a pipe [11], Reynolds observed that instability of the water in the pipe, the Reynolds num┬Ł ber Ua=┼Ī, exceeded a certain value, depending on the experimental
CFD simulation of aggregation and breakage processes in laminar Taylor¢Couette flow
L. Wang; D. L. Marchisio; R. D. Vigil; R. O. Fox
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of ?10Ā?m latex spheres suspended in an aqueous solution undergoing laminar Taylor¢Couette flow was carried out according to the following program. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry
Intensification of heat transfer at laminar stabilized flow of vapour-droplets in a tube
V. I. Terekhov; A. V. Chichindaev; M. A. Pakhomov
The numerical calculation heat- and mass transfer of a flow containing dispersed in liquid particles by a diameter 1...1000 microns is executed under normal physical conditions for laminar flow of a mode of. As a results of calculations the temperatures (gas vapour mixture and droplets), diameter of a drop both mass concentration vapour and liquids were defined. The decision includes
LE JOURNAL DE PHYSIQUE Flow birefringence study at the transition from laminar to
Boyer, Edmond
3371 LE JOURNAL DE PHYSIQUE Flow birefringence study at the transition from laminar to Taylor the birefringence induced by the flow in a liquid containing very fine particles in the vicinity of the transition but realistic hypotheses, we show that the extinction angle ~ and the birefringence 0394n of the solution
Measurement of temperature field in steady laminar free convection flow using digital holography
NASA Astrophysics Data System (ADS)
Shakher, Chandra; Hossain, Md. Mosarraf; Mehta, Dalip Singh; Sheoran, Gyanendra
A method to measure the temperature by visualizing the laminar free convection flow of water is presented by using digital holography in lensless Fourier transform configuration. Temperature is measured within the boundary layer of the convective flow field. The deviation in temperature measured by this method and from that of obtained by thermocouple is within 2%.
Measurement of temperature field in steady laminar free convection flow using digital holography
Chandra Shakher; Dalip Singh Mehta; Gyanendra Sheoran
A method to measure the temperature by visualizing the laminar free convection flow of water is presented by using digital holography in lensless Fourier transform configuration. Temperature is measured within the boundary layer of the convective flow field. The deviation in temperature measured by this method and from that of obtained by thermocouple is within 2%.
C. H. Huang; M. N. ųzisik
The conjugate gradient method is used to solve the inverse problem of determining the spacewise variation of an unknown applied wall flux for laminar flow inside a parallel plate duct. One of the walls is insulated. The inverse analysis is based on the temperature reading taken inside the fluid at several different locations along the flow. The inverse analysis is
Enhancement and reduction of Nusselt numbers in unsteady laminar parallel flows by macroscopic flow control
NASA Astrophysics Data System (ADS)
Jiang, Y.
In fully developed laminar pipe and channel flows that undergo transients from a known initial state, exact analytical solutions for the momentary velocity field as a functional of the flow rate can be determined from the Navier-Stokes equations, for arbitrary flow unsteadiness [Phys. Fluids 12, 3, 518, (2000)]. When these flows experience heat transfer at their walls, the companion thermal energy equation can be linearized and may also be solved analytically when flow transients are large. Under this restriction, solutions can be found for the instantaneous temperature field, for arbitrary time unsteadiness in both the flow and the wall heat flux. Expressions for Nusselt numbers in convective heat transfer in duct flows with arbitrary temporal flow and heat flux unsteadiness can then be found, which illustrate how the flow and heat flux transient histories determine whether the unsteadiness enhances or reduces the overall heat-transfer effectiveness. These expressions are used to show how significant enhancements or reductions in the average Nusselt number can be achieved in duct flow by applying appropriate temporal bulk-flow control.
Three-dimensional incompressible Navier-Stokes computations of internal flows
NASA Technical Reports Server (NTRS)
Kwak, D.; Chang, J. L. C.; Rogers, S. E.; Rosenfeld, M.; Kwak, D.
Several incompressible Navier-Stokes solution methods for obtaining steady and unsteady solutions are discussed. Special attention is given to internal flows which involve distinctly different features from external flows. The characterisitcs of the flow solvers employing the method of pseudocompressibility and a fractional step method are briefly described. This discussion is limited to a primitive variable formulation in generalized curvilinear coordinates. Computed results include simple test cases and internal flow in the Space Shuttle main engine hot-gas manifold.
Summary of Transition Results From the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport. Boundary-layer transition data on the titanium glove primarily have been obtained at speeds of Mach 2.0 and altitudes of 15,240-16,764 m (50,000-55,000 ft). The objectives of this flight experiment have been to achieve 0.50-0.60 chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point, a speed of Mach 1.9 at an altitude of 15,240 m (50,000 ft); but rather at a speed of Mach 2.0 and an altitude of 16,154 m (53,000 ft). Laminar flow has been obtained to more than 0.46 wing chord at a Reynolds number of 22.7 x 10(exp 6). A turbulence diverter has been used to initially obtain a laminar boundary layer at the attachment line. A lower-surface shock fence was required to block an inlet shock from the wing leading edge. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
Global Strong Solutions to Incompressible Nematic Liquid Crystal Flow
Jinkai Li
In this paper, we consider the Dirichlet problem of inhomogeneous incompressible nematic liquid crystal equations in bounded smooth domains of two or three dimensions. We prove the global existence and uniqueness of strong solutions with initial data being of small norm but allowed to have vacuum. More precisely, for two dimensional case, we only require that the basic energy $|\\sqrt{\\rho_0}u_0|_{L^2}^2+|\
High Reynolds Number Hybrid Laminar Flow Control (HLFC) Flight Experiment. Report 2; Aerodynamic Design
NASA Technical Reports Server (NTRS)
This document describes the aerodynamic design of an experimental hybrid laminar flow control (HLFC) wing panel intended for use on a Boeing 757 airplane to provide a facility for flight research on high Reynolds number HLFC and to demonstrate practical HLFC operation on a full-scale commercial transport airplane. The design consists of revised wing leading edge contour designed to produce a pressure distribution favorable to laminar flow, definition of suction flow requirements to laminarize the boundary layer, provisions at the inboard end of the test panel to prevent attachment-line boundary layer transition, and a Krueger leading edge flap that serves both as a high lift device and as a shield to prevent insect accretion on the leading edge when the airplane is taking off or landing.
Flight investigation of natural laminar flow on the Bellanca Skyrocket II
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Gregorek, G. M.; Hoffman, M. J.; Freuhler, R. J.
Two major concerns have inhibited the use of natural laminar flow (NLF) for viscous drag reduction on production aircraft. These are the concerns of achieveability of NLF on practical airframe surfaces, and maintainability in operating environments. Previous research in this area left a mixture of positive and negative conclusions regarding these concerns. While early (pre-1950) airframe construction methods could not achieve NLF criteria for waviness, several modern construction methods (composites for example) can achieve the required smoothness. This paper presents flight experiment data on the achieveability and maintainability of NLF on a high-performance, single-propeller, composite airplane, the Bellanca Skyrocket II. The significant contribution of laminar flow to the performance of this airplane was measured. Observations of laminar flow in the propeller slipstream are discussed, as are the effects of insect contamination on the wing. These observations have resulted in a new appreciation of the operational feasibility for achieving and maintaining NLF on modern airframe surfaces.
Natural Laminar-Flow blades for vertical-axis wind turbines
Klimas, P.C.
Natural Laminar Flow (NLF) airfoils are those which can achieve significant extents of laminar flow (greater than 30% of chord) solely through favorable pressure gradients. A number of candidate airfoil sections were defined and then screened in a performance simulation. The section selected for fabrication and test was one which supported a 47% chord laminar flow. A comparison of lift and drag coefficients is made. A two-blade set was extruded for a 5-m diameter vertical axis wind turbine. A test series was then conducted at a turbine rotational speed of 175 rpm and a corresponding equatorial Reynolds number of 360,000. Field and wind tunnel tests have been and will be conducted. (LEW)
Parametric study on laminar flow for finite wings at supersonic speeds
NASA Technical Reports Server (NTRS)
Garcia, Joseph Avila
Laminar flow control has been identified as a key element in the development of the next generation of High Speed Transports. Extending the amount of laminar flow over an aircraft will increase range, payload, and altitude capabilities as well as lower fuel requirements, skin temperature, and therefore the overall cost. A parametric study to predict the extent of laminar flow for finite wings at supersonic speeds was conducted using a computational fluid dynamics (CFD) code coupled with a boundary layer stability code. The parameters investigated in this study were Reynolds number, angle of attack, and sweep. The results showed that an increase in angle of attack for specific Reynolds numbers can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag, due to the delay in transition, can be expected simultaneously. This results in larger payload and range.
Digital data acquisition and preliminary instrumentation study for the F-16 laminar flow control vehicle
NASA Technical Reports Server (NTRS)
Ostowari, Cyrus
Preliminary studies have shown that maintenance of laminar flow through active boundary-layer control is viable. Current research activity at NASA Langley and NASA Dryden is utilizing the F-16XL-1 research vehicle fitted with a laminar-flow suction glove that is connected to a vacuum manifold in order to create and control laminar flow at supersonic flight speeds. This experimental program has been designed to establish the feasibility of obtaining laminar flow at supersonic speeds with highly swept wing and to provide data for computational fluid dynamics (CFD) code calibration. Flight experiments conducted as supersonic speeds have indicated that it is possible to achieve laminar flow under controlled suction at flight Mach numbers greater than 1. Currently this glove is fitted with a series of pressure belts and flush mounted hot film sensors for the purpose of determining the pressure distributions and the extent of laminar flow region past the stagnation point. The present mode of data acquisition relies on out-dated on board multi-channel FM analogue tape recorder system. At the end of each flight, the analogue data is digitized through a long laborious process and then analyzed. It is proposed to replace this outdated system with an on board state-of-the-art digital data acquisition system capable of a through put rate of up to 1 MegaHertz. The purpose of this study was three-fold: (1) to develop a simple algorithm for acquiring data via 2 analogue-to-digital convertor boards simultaneously (total of 32 channels); (2) to interface hot-film/wire anemometry instrumentation with a PCAT type computer; and (3) to characterize the frequency response of a flush mounted film sensor. A brief description of each of the above tasks along with recommendations are given.
Flow-field characterization of DBD plasma actuators as discrete roughness elements for laminar flow control
NASA Astrophysics Data System (ADS)
Craig, S. A.; Humble, R. A.; Hofferth, J. W.; Saric, W. S.
For many years there has been an evolving interest in controlling boundary layer transition on swept-wings. With an appropriate distribution of spanwise-periodic discrete roughness elements (DRE), subcritical wavelengths can be excited which supersede the growth of the most-amplified wavelength, thereby delaying the crossflow-dominated laminar-turbulent transition. To elucidate the physics of annular DBD plasma actuators for potential use as DRE and facilitate effective design, they are studied under quiescent flow conditions using particle image velocimetry a photomultiplier tube (PMT) and a high-speed camera. A complex flow-field is generated by a single aperture that describes a three-dimensional torus accompanied by a downward, wall-normal jet region. The flow-field is sensitive to aperture size and applied voltage. For arrayed actuators, the tori contract dramatically due to the interaction with vortices from adjacent apertures. A PMT in conjunction with a high-speed camera were used to observe the light intensity from the bulk plasma at high temporal resolution and visualize the individual discharge events. Supported by the NASA/AFOSR National Center for Hypersonic Laminar-Turbulent Transition Research.
A flight test investigation of certification requirements for laminar-flow general aviation airplanes
NASA Technical Reports Server (NTRS)
Manuel, Gregory S.; Doty, Wayne A.
A modified T210R general aviation aircraft incorporating natural laminar flow (NLF) technology has been subjected to flight tests in order to evaluate its stability and control characteristics. Attention is given to this aircraft's ability to meet certification requirements with significant NLF, as well as with the boundary-layer transition fixed near the leading edge. It is established that the large regions of NLF achieved yielded a significant cruise performance enhancement; loss of laminar flow did not result in significant changes in the stability and control characteristics of the aircraft. FAR Part 23 certification requirements were met.
A short note on the discontinuous Galerkin discretization of the pressure projection operator in incompressible flow
NASA Astrophysics Data System (ADS)
Steinmoeller, D. T.; Stastna, M.; Lamb, K. G.
This note reports on the issue of spurious compressibility artifacts that can arise when the popular pressure projection (PP) method is used for unsteady simulations of incompressible flow using the symmetric interior penalty discontinuous Galerkin (SIP-DG) method. Through a spectral analysis of the projection operator's SIP-DG discretization, we demonstrate that the eigenfunctions of the operator do not form a basis that allows for the correct enforcement of the incompressibility constraint. This short-coming can cause numerical instabilities for inviscid, advection-dominated, and density stratified flow simulations, especially for long-time integrations and/or under-resolved situations. To remedy this problem, we propose a local post-processing projection that enforces incompressibility exactly to allow for stable and robust long-time integrations.
Aerodynamic design of a midsized vertical-axis wind turbine using natural laminar-flow blade elements
P. C. Klimas; D. E. Berg
Natural laminar-flow (NLF) airfoils are those which can achieve significant extents of laminar flow (greater than or equal to 30% chord) solely through favorable pressure gradients. Studies have shown that vertical-axis wind turbines (VAWTs) using NLF sections as blade elements have the potential of producing energy at a significantly lower cost (approx. =20%) than turbines of current design. Sandia National
A Numerical Study of Displacement Body and Curvature Effects on Incompressible and Compressible Laminar Boundary Layers. Ph.D. Thesis - Va. Polytechnic Inst.
NASA Technical Reports Server (NTRS)
Wornom, S. F.
This technique has been applied to study such effects on incompressible flow around cylinders at moderate to low Reynolds numbers and for compression ramps at hypersonic Mach numbers by employing a finite difference method to obtain numerical solutions. The results indicate that the technique can be applied successfully in both regimes and does predict the correct trend in regions of large curvature and displacement body effects. It was concluded that curvature corrections should only be attempted in cases where all displacement effects can be fully accounted for.
Approximate factorization with an elliptic pressure solver for incompressible flow
NASA Technical Reports Server (NTRS)
Bernard, R. S.; Thompson, J. F.
Two-dimensional curvilinear coordinates are used to solve the incompressible Navier-Stokes equations, in conjunction with approximate factorization for the solution of the momentum equation and the successive overrelaxation by lines method for the solution of a Poisson equation for the pressure. The combined algorithm, although not fully explicit, is marginally stable at Reynolds numbers lower than 10,000 and time increments of 0.01. Pressure distributions calculated for attack angles of zero and 6 deg are of the same shape as the experimental curves, but are shifted to one side.
Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers
A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.
Analysis of Compressible and Incompressible Flows Through See-through Labyrinth SealsĀ
Woo, Jeng Won
effect on the discharge coefficient. In particular, for compressible fluid under certain flow and seal geometric conditions, the discharge coefficient did not increase with an increase in the Reynolds number. It was correlated to the pressure ratio, g...1842g1870. Moreover, it was also related to the fact that the flow of the fluid through the constriction became compressible and the flow eventually became choked. At low pressure ratios (less than 0.7), Saikishan?s incompressible model deviated from...
Feasibility and benefits of laminar flow control on supersonic cruise airplanes
NASA Technical Reports Server (NTRS)
Powell, A. G.; Agrawal, S.; Lacey, T. R.
An evaluation was made of the applicability and benefits of laminar flow control (LFC) technology to supersonic cruise airplanes. Ancillary objectives were to identify the technical issues critical to supersonic LFC application, and to determine how those issues can be addressed through flight and wind-tunnel testing. Vehicle types studied include a Mach 2.2 supersonic transport configuration, a Mach 4.0 transport, and two Mach 2-class fighter concepts. Laminar flow control methodologies developed for subsonic and transonic wing laminarization were extended and applied. No intractible aerodynamic problems were found in applying LFC to airplanes of the Mach 2 class, even ones of large size. Improvements of 12 to 17 percent in lift-drag ratios were found. Several key technical issues, such as contamination avoidance and excresence criteria were identified. Recommendations are made for their resolution. A need for an inverse supersonic wing design methodology is indicated.
Dispersion of swimming algae in laminar and turbulent channel flows: theory and simulations
Croze, O A; Ahmed, M; Bees, M A; Brandt, L
Algal swimming is often biased by environmental cues, e.g. gravitational and viscous torques drive cells towards downwelling fluid (gyrotaxis). In view of biotechnological applications, it is important to understand how such biased swimming affects cell dispersion in a flow. Here, we study the dispersion of gyrotactic swimming algae in laminar and turbulent channel flows. By direct numerical simulation (DNS) of cell motion within upwelling and downwelling channel flows, we evaluate time-dependent measures of dispersion for increasing values of the flow Peclet (Reynolds) numbers, Pe (Re). Furthermore, we derive an analytical `swimming Taylor-Aris dispersion' theory, using flow-dependent transport parameters given by existing microscopic models. In the laminar regime, DNS results and analytical predictions compare very well, providing the first confirmation that cells' response to flow is best described by the generalized-Taylor-dispersion microscopic model. We predict that cells drift along a channel faster th...
Air Flow in a Separating Laminar Boundary Layer
NASA Technical Reports Server (NTRS)
Schubauer, G B
The speed distribution in a laminar boundary layer on the surface of an elliptic cylinder, of major and minor axes 11.78 and 3.98 inches, respectively, has been determined by means of a hot-wire anemometer. The direction of the impinging air stream was parallel to the major axis. Special attention was given to the region of separation and to the exact location of the point of separation. An approximate method, developed by K. Pohlhausen for computing the speed distribution, the thickness of the layer, and the point of separation, is described in detail; and speed-distribution curves calculated by this method are presented for comparison with experiment.
Numerical simulation of the incompressible internal flow through a tilting disk valve
NASA Technical Reports Server (NTRS)
Chang, I-Dee; Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin
A numerical simulation of the incompressible viscous flow through a prosthetic tilting disk heart valve is presented in order to demonstrate the current capability to model unsteady flows with moving boundaries. Both steady and unsteady flow calculations are performed by solving the incompressible Navier-Stokes equations in three-dimensional generalized curvilinear coordinates. In order to handle the moving boundary problems, the chimera grid embedding scheme which decomposes a complex computational domain into several simple subdomains is used. An algebraic turbulence model for internal flows is incorporated to reach the physiological values of Reynolds number. Good agreement is obtained between the numerical results and experimental measurements. It is found that the tilting disk valve causes large regions of separated flow, and regions of high shear.
Finite element analysis of incompressible and compressible fluid flows with free surfaces and structural interactions
K. J. Bathe; H. Zhang; M. H. Wang
We present the current ADINA-F capabilities for fluid flow analysis. The fluid can be considered to be an incompressible or compressible medium. Free surfaces and the full interactions with structures in two- and three-dimensional conditions can be analyzed. The basic formulations and finite element discretizations used are described, the techniques for the solution of the finite element equations are briefly
Progress in incompressible Navier-Stokes computations for propulsion flows and its dual-use applications
NASA Technical Reports Server (NTRS)
Kiris, Cetin
Development of an incompressible Navier-Stokes solution procedure was performed for the analysis of a liquid rocket engine pump components and for the mechanical heart assist devices. The solution procedure for the propulsion systems is applicable to incompressible Navier-Stokes flows in a steadily rotating frame of reference for any general complex configurations. The computer codes were tested on different complex configurations such as liquid rocket engine inducer and impellers. As a spin-off technology from the turbopump component simulations, the flow analysis for an axial heart pump was conducted. The baseline Left Ventricular Assist Device (LVAD) design was improved by adding an inducer geometry by adapting from the liquid rocket engine pump. The time-accurate mode of the incompressible Navier-Stokes code was validated with flapping foil experiment by using different domain decomposition methods. In the flapping foil experiment, two upstream NACA 0025 foils perform high-frequency synchronized motion and generate unsteady flow conditions for a downstream larger stationary foil. Fairly good agreement was obtained between unsteady experimental data and numerical results from two different moving boundary procedures. Incompressible Navier-Stokes code (INS3D) has been extended for heat transfer applications. The temperature equation was written for both forced and natural convection phenomena. Flow in a square duct case was used for the validation of the code in both natural and forced convection.
Adaptive Mesh Refinement for Singular Current Sheets in Incompressible Magnetohydrodynamic Flows
Holger Friedel; Rainer Grauer; Christiane Marliani
The formation of current sheets in ideal incompressible magnetohydrodynamic flows in two dimensions is studied numerically using the technique of adaptive mesh refinement. The growth of current density is in agreement with simple scaling assumptions. As expected, adaptive mesh refinement shows to be very efficient for studying singular structures compared to non-adaptive treatments.
Time accuracy and spurious transients of projection methods for viscous incompressible flows
Buscaglia, Gustavo C.
Time accuracy and spurious transients of projection methods for viscous incompressible flows considered result from algebraically splitting the linear system corresponding to each time step of first, second and third order in the time step size t are obtained, depending on the method. The methods
INFORMATION ISSN 1343-4500 Computing an Incompressible Viscous Fluid Flow Using Neural Network Based
INFORMATION ISSN 1343-4500 Computing an Incompressible Viscous Fluid Flow Using Neural Network Neural Networks (ANN) with Modified Adaptive Smoothing Errors (MASE) based on back-propagation algorithm of the learning system are in good agreement with the available previous works. Key Words: learning system; neural
P. Vellando; J. Puertas; J. Bonillo; J. Fe
A Finite Element based program has been released to solve the steady 2D Navier - Stokes equations. The mixed-variable algorithm is used as a first approach to solve the differential problem. In order to reduce the number of equations, both a penalty and segregated formulation are implemented to give solution to the viscous incompressible flow and their results are compared
Shape sensitivity analysis of time-dependent flows of incompressible non-Newtonian fluids
Paris-Sud XI, Universitķ de
Shape sensitivity analysis of time-dependent flows of incompressible non-Newtonian fluids J. Fluids whose viscosity depends on the shear rate through (1) form an impor- tant class of non-Newtonian viscous fluid of power-law type. The fluid is confined to a bounded planar domain surrounding an obstacle
Modeling and Simulation of Nanoparticle Coagulation in High Reynolds Number Incompressible Flows
Zachariah, Michael R.
Modeling and Simulation of Nanoparticle Coagulation in High Reynolds Number Incompressible Flows S and growth (coagulation/coalescence, condensation, etc). Sundaram and Collins2 investigated the influence to coagulation and found that the magnitude of the minimum particle collision frequency was more strongly
Finite-difference immersed boundary method consistent with wall conditions for incompressible turbulent flow simulations
Tsutomu Ikeno; Takeo Kajishima
An immersed boundary method to achieve the consistency with a desired wall velocity was developed. Existing schemes of immersed boundary methods for incompressible flow violate the wall condition in the discrete equation system during time-advancement. This problem arises from the inconsistency of the pressure with the velocity interpolated to represent the solid wall, which does not coincide with the computational
Treatment of incompressibility and boundary conditions in 3-D numerical spectral simulations of plane channel flows
L. Kleiser; U. Schumann
A spectral method for numerical computation of 3-D time-dependent incompressible flows between two plane parallel plates is presented. Fourier expansions in the coordinates parallel to the walls and expansions in Chebyshev polynomials in the normal coordinate are used. The time coordinate is discretized with second order finite differences, treating the viscous terms implicitly. An efficient direct solution procedure for the
Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors.
Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca
Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Pķclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Pķclet number. The cell effective axial diffusivity increases and decreases with Pķclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design. PMID:23407572
Generalized similarity solutions for three dimensional, laminar, steady, compressible boundary layer flows on swept profile cylinders
Viktor Saljnikov; Uwe Dallmann
A method of generalized similarity which allows one to derive solutions of the laminar, steady, compressible, and 3-D boundary layer equations for swept wing configurations is presented. The model configuration is an infinitely long swept profile cylinder within ideal gas flow with a dynamic viscosity which depends linearly on the temperature. The pressure distribution, Pr and Ma numbers, as well
A wind tunnel study was performed to determine the dispersion characteristics of gas jets with densities heavier than that of air. he experiments were done in a laminar cross-flow and then repeated in a turbulent boundary layer. ll major boundary-layer characteristics were measur...
Exact solution of Nusselt problem for laminar fluid flow in a round tube
V. Gasenko
Nusselt heat exchange problem for steady state laminar fluid flow in a round tube was solved exactly as a row of eigenfunctions with decomposition coefficients being depended of initial temperature profile on tube inlet. These eigenfunctions in turn was found to be exponential row of radius coordinate with coefficients to be a function of eigenvalues. Analytical expression for eigenvalues was
Copyright 2009 by ASME Laminar fully developed flow in streamwise-periodic
Bahrami, Majid
1 Copyright ®2009 by ASME ABSTRACT Laminar fully developed flow in streamwise of FEDSM2009 2009 ASME Fluid Engineering Division Summer Meeting and Exhibition August 2-5, 2009, Vail;2 Copyright ®2009 by ASME Table 1. Some of the previous works on varying-cross section channels author year
Laminar Heat Transfer of a Swirled Flow in a Conical Diffuser. Self-similar Solution
I. V. Shevchuk
Heat transfer in a laminar swirled air flow in the divergent channel between a disk and a cone whose vertex touches the disk is studied. A self-similar solution of the Navier-Stokes and energy equations is derived using group analysis. An exact numerical solution of the problem is obtained for different radial-to-tangential velocity ratios at the channel inlet.
Three-dimensionality of sand ripples under steady laminar shear flow
Three-dimensionality of sand ripples under steady laminar shear flow V. Langlois and A. Valance 11 October 2005. [1] We investigate the formation of three-dimensional sand patterns under a steady in the infinite depth case and in the long-wavelength approximation. The sand transport is described using two
Formation of Two-Dimensional Sand Ripples under Laminar Shear Flow Vincent Langlois and Alexandre Valance
Formation of Two-Dimensional Sand Ripples under Laminar Shear Flow Vincent Langlois and Alexandre 20 June 2005) The process of ripple formation on a two-dimensional sand bed sheared by a viscous fluid is investigated theoretically. The sand transport is described taking into account both the local
A parametric wing design study for a modern laminar flow wing
NASA Technical Reports Server (NTRS)
Koegler, J. A., Jr.
The results of a parametric wing design study using a modern laminar flow airfoil designed to exhibit desirable stall characteristics while maintaining high cruise performance are presented. It was found that little is sacrificed in cruise performance when satisfying the stall margin requirements if a taper ratio of 0.65 or greater is used.
Polymer Brushes Patterned with Micrometer-Scale Chemical Gradients Using Laminar Co-Flow
Braun, Paul
Polymer Brushes Patterned with Micrometer-Scale Chemical Gradients Using Laminar Co-Flow Hyung) polymer brush. The spatial distribution of the quaternized polymer brush is characterized by confocal Raman microscopy. The quaternization gradient length in the polymer brush can be varied
Improved approximate method for simulating frequency-dependent friction in transient laminar flow
G. A. Schohl
A new approximation to the weighting function in Zielke's equation is used in an improved implementation of Trikha's method for including frequency dependent friction in transient laminar flow calculations. The new, five-term approximation was fitted to the weighting function using a nonlinear least squares approach. Transient results obtained using the new approximation function are nearly indistinguishable from results obtained using
Laminar radial flow electrochemical reactors. II. Convective diffusion of inert tracer
F. B. Thomas; P. A. Ramachandran; M. P. Dudukovic; R. E. W. Jansson
Mixing is investigated in three laminar radial flow cells (capillary gap cell (stationary discs), pump cell (one disc spinning) and the rotating electrolyser (co-rotating discs)) using numerical and semianalytical methods for inert tracer transport. Results are compared to existing data. Mixing in the three cells is modelled using finite element techniques applied to convection-dominated inert tracer transport. For the capillary
Ultraviolet disinfection of juice products in laminar and turbulent flow reactors
Tatiana Koutchma; Susanne Keller; Stuart Chirtel; Brian Parisi
Individual physical and chemical factors were examined in a model fluid for their effects on the efficacy of UV light on the destruction of Escherichia coli K-12 bacteria using laminar and turbulent flow treatment systems. Factors unique to juice, such as Brix and pH, did not exhibit a large effect over the range tested when examined individually. The single factor
A macroscopic agglomeration kernel model for gibbsite precipitation in turbulent and laminar flows
I. Livk; D. Ilievski
A macroscopic agglomeration kernel model has been developed that is capable of describing gibbsite agglomeration over a broad range of process conditions, including both the laminar and turbulent flow regimes. The agglomeration kernel model was derived using chemical reaction engineering principles and data from an extensive experimental program covering a wide range of temperatures, supersaturations, seed sizes, shear rates and
Two-fluid modeling of aerosol transport in laminar and turbulent flows
P. Armand; D. Boulaud; M. Pourprix; J. Vendel
The two-fluid model has been adapted to dilute dispersions of dense inclusions (i.e. particles) carried by laminar or turbulent flows where an exchange of momentum takes place between particles and fluid. It is assumed that the medium is isothermal and free of phase change. The model is used to simulate different experimental applications and the simulations are compared to the
An experimental investigation of transitional instabilities in laminar separation bubble flows on airfoils at low Reynolds numbers
NASA Astrophysics Data System (ADS)
LeBlanc, Patrick J.
A new parallel implicit adaptive mesh refinement (AMR) algorithm is developed for the prediction of unsteady behaviour of laminar flames. The scheme is applied to the solution of the system of partial-differential equations governing time-dependent, two- and three-dimensional, compressible laminar flows for reactive thermally perfect gaseous mixtures. A high-resolution finite-volume spatial discretization procedure is used to solve the conservation form of these equations on body-fitted multi-block hexahedral meshes. A local preconditioning technique is used to remove numerical stiffness and maintain solution accuracy for low-Mach-number, nearly incompressible flows. A flexible block-based octree data structure has been developed and is used to facilitate automatic solution-directed mesh adaptation according to physics-based refinement criteria. The data structure also enables an efficient and scalable parallel implementation via domain decomposition. The parallel implicit formulation makes use of a dual-time-stepping like approach with an implicit second-order backward discretization of the physical time, in which a Jacobian-free inexact Newton method with a preconditioned generalized minimal residual (GMRES) algorithm is used to solve the system of nonlinear algebraic equations arising from the temporal and spatial discretization procedures. An additive Schwarz global preconditioner is used in conjunction with block incomplete LU type local preconditioners for each sub-domain. The Schwarz preconditioning and block-based data structure readily allow efficient and scalable parallel implementations of the implicit AMR approach on distributed-memory multi-processor architectures. The scheme was applied to solutions of steady and unsteady laminar diffusion and premixed methane-air combustion and was found to accurately predict key flame characteristics. For a premixed flame under terrestrial gravity, the scheme accurately predicted the frequency of the natural buoyancy induced oscillations. The performance of the proposed parallel implicit algorithm was assessed by comparisons to more conventional solution procedures and was found to significantly reduce the computational time required to achieve a solution in all cases investigated.
Laminar and turbulent nozzle-jet flows and their acoustic near-field
NASA Astrophysics Data System (ADS)
B³hler, Stefan; Obrist, Dominik; Kleiser, Leonhard
We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of ReD = 18 100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.
Preliminary Investigation of Certain Laminar-Flow Airfoils for Application at High Speeds and Reynolds Numbers
NASA Technical Reports Server (NTRS)
Jacobs, E.N.; Abbott, Ira H.; von Doenhoff, A.E.
In order to extend the useful range of Reynolds numbers of airfoils designed to take advantage of the extensive laminar boundary layers possible in an air stream of low turbulence, tests were made of the NACA 2412-34 and 1412-34 sections in the NACA low-turbulence tunnel. Although the possible extent of the laminar boundary layer on these airfoils is not so great as for specially designed laminar-flow airfoils, it is greater than that for conventional airfoils, and is sufficiently extensive so that at Reynolds numbers above 11,000,000 the laminar region is expected to be limited by the permissible 'Reynolds number run' and not by laminar separation as is the case with conventional airfoils. Drag measurements by the wake-survey method and pressure-distribution measurements were made at several lift coefficients through a range of Reynolds numbers up to 11,400,000. The drag scale-effect curve for the NACA 1412-34 is extrapolated to a Reynolds number of 30,000,000 on the basis of theoretical calculations of the skin friction. Comparable skin-friction calculations were made for the NACA 23012. The results indicate that, for certain applications at moderate values of the Reynolds number, the NACA 1412-34 and 2412-34 airfoils offer some advantages over such conventional airfoils as the NACA 23012. The possibility of maintaining a more extensive laminar boundary layer on these airfoils should result in a small drag reduction, and the absence of pressure peaks allows higher speeds to be reached before the compressibility burble is encountered. At lower Reynold numbers, below about 10,000,000, these airfoils have higher drags than airfoils designed to operate with very extensive laminar boundary layers.
A high-order incompressible flow solver with WENO
NASA Astrophysics Data System (ADS)
Zhang, Ju; Jackson, Thomas L.
A numerical method for solving the incompressible Navier-Stokes equations with a 5th-order weighted essentially non-oscillatory (WENO) scheme is presented. The method is not based on artificial compressibility and is free of tunable parameters such as the artificial compressibility parameter. The method makes use of the fractional-step method in conjunction with the low-dissipation and low-dispersion Runge-Kutta (LDDRK) scheme to improve temporal accuracy of the scheme. The use of a WENO scheme makes it possible to obtain stable solutions for discontinuous initial data and resolve difficult applications with strong shear such as Kelvin-Helmholtz instability or turbulence. Good convergence rate is established for the velocity variables and numerical solutions of the present method compare well with exact solutions and other numerical results.
A regularized Lagrangian finite point method for the simulation of incompressible viscous flows
NASA Astrophysics Data System (ADS)
Fang, Jiannong; Parriaux, AurĶle
In this paper we present a regularized Lagrangian finite point method (RLFPM) for the numerical simulation of incompressible viscous flows. A Lagrangian finite point scheme is applied to the projection method for the incompressible Navier-Stokes equations. The approximation of spatial derivatives is obtained by the weighted least squares method. The pressure Poisson equation with Neumann boundary condition is solved by a stabilized finite point method. A key aspect of the present approach is the periodic redistribution of the particle locations, which are being distorted by the flow. Again, weighted least squares approximation is implemented to interpolate the properties of the old particles onto the new particle locations. With the proposed regularization technique, problems associated with the flow-induced irregularity of particle distribution in the Lagrangian finite point scheme are circumvented. Three numerical examples, Taylor-Green flow, lid-driven flow in a cavity and flow through a periodic lattice of cylinders, are presented to validate the proposed methodology. The problem of extra diffusion caused by regularization is discussed. The results demonstrate that RLFPM is able to perform accurate and stable simulations of incompressible viscous flows.
Incompressible viscous flow computations for the pump components and the artificial heart
NASA Technical Reports Server (NTRS)
Kiris, Cetin
A finite-difference, three-dimensional incompressible Navier-Stokes formulation to calculate the flow through turbopump components is utilized. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Both steady and unsteady flow calculations can be performed using the current algorithm. In this work, the equations are solved in steadily rotating reference frames by using the steady-state formulation in order to simulate the flow through a turbopump inducer. Eddy viscosity is computed by using an algebraic mixing-length turbulence model. Numerical results are compared with experimental measurements and a good agreement is found between the two. Included in the appendix is a paper on incompressible viscous flow through artificial heart devices with moving boundaries. Time-accurate calculations, such as impeller and diffusor interaction, will be reported in future work.
Analysis and evaluation of an integrated laminar flow control propulsion system
NASA Technical Reports Server (NTRS)
Keith, Theo G., Jr.; Dewitt, Kenneth J.
Reduction of drag has been a major goal of the aircraft industry as no other single quantity influences the operating costs of transport aircraft more than aerodynamic drag. It has been estimated that even modest reduction of frictional drag could reduce fuel costs by anywhere from 2 to 5 percent. Current research on boundary layer drag reduction deals with various approaches to reduce turbulent skin friction drag as a means of improving aircraft performance. One of the techniques belonging to this category is laminar flow control in which extensive regions of laminar flow are maintained over aircraft surfaces by delaying transition to turbulence through the ingestion of boundary layer air. While problems of laminar flow control have been studied in some detail, the prospect of improving the propulsion system of an aircraft by the use of ingested boundary layer air has received very little attention. An initial study for the purpose of reducing propulsion system requirements by utilizing the kinetic energy of boundary layer air was performed in the mid-1970's at LeRC. This study which was based on ingesting the boundary layer air at a single location, did not yield any significant overall propulsion benefits; therefore, the concept was not pursued further. However, since then it has been proposed that if the boundary layer air were ingested at various locations on the aircraft surface instead of just at one site, an improvement in the propulsion system might be realized. The present report provides a review of laminar flow control by suction and focuses on the problems of reducing skin friction drag by maintaining extensive regions of laminar flow over the aircraft surfaces. In addition, it includes an evaluation of an aircraft propulsion system that is augmented by ingested boundary layer air.
Formation of a laminar electron flow for 300 GHz high-power pulsed gyrotron
Yamaguchi, Yuusuke; Tatematsu, Yoshinori; Saito, Teruo; Ikeda, Ryosuke; Mudiganti, Jagadish C.; Ogawa, Isamu; Idehara, Toshitaka [Research Center for Development of Far-Infrared Region, University of Fukui, 3-9-1 Bunkyo, Fukui-shi 910-8507 (Japan)
This paper describes the design of a triode magnetron injection gun for use in a 200 kW, 300 GHz gyrotron. As power and frequency increase, the performance of the gyrotron becomes quite sensitive to the quality of the electron beam. Formation of a laminar electron flow is essential for the realization of a high quality beam with a small velocity spread. In this study, a new method is developed for a quantitative evaluation of the laminarity and is applied to optimize the electrode design. The laminarity depends not only on conventional design parameters such as the cathode slant angle but also on the spatial distribution of the electric field along the beam trajectory. In the optimized design, the velocity pitch factors, {alpha}, larger than 1.2 are obtained at 65 kV, 10 A with spreads, {Delta}{alpha}, less than 5%.
A Unified Method for Computing Incompressible and Compressible Flows in Boundary-Fitted Coordinates
Hester Bijl; Pieter Wesseling
A unified method for computing incompressible and compressible flows with Mach-uniform accuracy and efficiency is described. The method is equally applicable to stationary and nonstationary flows. A pressure-based discretisation on a staggered grid in general boundary-fitted coordinates is used for the Euler equations. Extension to Navier--Stokes is straightforward. Dimensionless variables that remain finite for all Mach numbers are used. Mach
Je-Hoon Kim; Kenneth E. Jansen; Michael K. Jensen
A stabilized finite-element solver is used to solve turbulent flows and heat transfer in complex, three-dimensional geometries. Selected turbulence models are implemented and evaluated for their performance. Particular attention is given to the initial conditions for k and ? necessary to facilitate convergence. Details of the stabilized finite-element formulations for incompressible flow are also presented, and cost-effective model simplifications are
On a modification of GLS stabilized FEM for solving incompressible viscous flows
NASA Astrophysics Data System (ADS)
Burda, P.; Novotn², J.; ═stek, J.
We deal with 2D flows of incompressible viscous fluids with high Reynolds numbers. Galerkin Least Squares technique of stabilization of the finite element method is studied and its modification is described. We present a number of numerical results obtained by the developed method, showing its contribution to solving flows with high Reynolds numbers. Several recommendations and remarks are included. We are interested in positive as well as negative aspects of stabilization, which cannot be divorced.
Implicit Time Integration Schemes for the Unsteady Compressible Navier¢Stokes Equations: Laminar Flow
Hester Bijl; Mark H. Carpenter; Veer N. Vatsa; Christopher A. Kennedy
The accuracy and efficiency of several lower and higher order time integration schemes are investigated for engineering solution of the discretized unsteady compressible Navier¢Stokes equations. Fully implicit methods tested are either the backward differentiation formulas (BDF) or stage-order two, explicit, singly diagonally implicit Runge¢Kutta (ESDIRK) methods. For this comparison an unsteady two-dimensional laminar flow problem is chosen: flow around a
Experimental investigation into convective heat transfer of nanofluids at the entrance region under laminar flow conditions
Dongsheng Wen; Yulong Ding
This paper reports an experimental work on the convective heat transfer of nanofluids, made of ?-Al2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime. The results showed considerable enhancement of convective heat transfer using the nanofluids. The enhancement was particularly significant in the entrance region, and was much higher than that solely due to
Stable and accurate pressure approximation for unsteady incompressible viscous flow
NASA Astrophysics Data System (ADS)
Liu, Jian-Guo; Liu, Jie; Pego, Robert L.
How to properly specify boundary conditions for pressure is a longstanding problem for the incompressible Navier-Stokes equations with no-slip boundary conditions. An analytical resolution of this issue stems from a recently developed formula for the pressure in terms of the commutator of the Laplacian and Leray projection operators. Here we make use of this formula to (a) improve the accuracy of computing pressure in two kinds of existing time-discrete projection methods implicit in viscosity only, and (b) devise new higher-order accurate time-discrete projection methods that extend a slip-correction idea behind the well-known finite-difference scheme of Kim and Moin. We test these schemes for stability and accuracy using various combinations of C0 finite elements. For all three kinds of time discretization, one can obtain third-order accuracy for both pressure and velocity without a time-step stability restriction of diffusive type. Furthermore, two kinds of projection methods are found stable using piecewise-linear elements for both velocity and pressure.
Experimental study of the instability of laminar flow in a tube with deformable walls
NASA Astrophysics Data System (ADS)
Neelamegam, R.; Shankar, V.
The onset of instability of laminar flow in a tube with deformable walls is studied experimentally in order to characterize how the onset is affected by the elastic (shear) modulus of the deformable wall. To this end, rectangular blocks of polydimethylsiloxane (PDMS) gels of different shear moduli are fabricated with a cylindrical hole (of diameter 1.65 mm) in which the fluid (water) flow occurs due to an imposed pressure difference. The shear moduli of the PDMS gels were in the range of 21 - 608 kPa. When fluid flows through the deformable tube, we find that the tube radius changes slowly as a function of distance along the flow, and this change is a function of Reynolds number (Re). The pressure drop between the two ends of the tube is measured, and the friction factor is calculated from this pressure drop. The friction factor vs. Re data shows that the expected laminar flow relation (f = 64/Re) for flow in a rigid tube is seen in a deformable tube at lower Re, but there is a deviation from this relation at Re < 2000. We identify the Re at which the deviation occurs as the Reynolds number at which the laminar flow in the deformable tube becomes unstable. This transition Reynolds number is as low as 500 for the 21 kPa PDMS gel, the softest gel studied in this work, and this value is much lower than the critical Reynolds number (ś2000) for transition in a rigid tube. The onset of the transition is also independently corroborated using a dye-stream visualization method, and the transition Reynolds number obtained with this method agrees well with the Reynolds number at which there is a deviation in the friction-factor data from the laminar relation. This transition in a deformable tube which happens at Reynolds number much lower than 2000 could be potentially exploited in improving mixing in microscale devices.
Numerical simulation methods of incompressible flows and an application to the space shuttle main engine
NASA Technical Reports Server (NTRS)
Chang, J. L. C.; Kwak, D.; Rogers, S. E.; Yang, R.-J.
Incompressible Navier-Stokes solution methods are discussed with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow-solver code was used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current engine analysis and the redesign effort are discussed along with experimental results. This example demonstrates the potential of computational fluid dynamics as a design tool for aerospace applications.
A theoretical method for the analysis and design of axisymmetric bodies. [flow distribution and incompressible fluids
NASA Technical Reports Server (NTRS)
Beatty, T. D.
A theoretical method is presented for the computation of the flow field about an axisymmetric body operating in a viscous, incompressible fluid. A potential flow method was used to determine the inviscid flow field and to yield the boundary conditions for the boundary layer solutions. Boundary layer effects in the forces of displacement thickness and empirically modeled separation streamlines are accounted for in subsequent potential flow solutions. This procedure is repeated until the solutions converge. An empirical method was used to determine base drag allowing configuration drag to be computed.
Simulated-airline-service flight tests of laminar-flow control with perforated-surface suction system
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Braslow, Albert L.
The effectiveness and practicality of candidate leading edge systems for suction laminar flow control transport airplanes were investigated in a flight test program utilizing a modified JetStar airplane. The leading edge region imposes the most severe conditions on systems required for any type of laminar flow control. Tests of the leading edge systems, therefore, provided definitive results as to the feasibility of active laminar flow control on airplanes. The test airplane was operated under commercial transport operating procedures from various commercial airports and at various seasons of the year.
Laminar: Practical Fine-Grained Decentralized Information Flow Control
McKinley, Kathryn S.
information flow control (DIFC) is a promising model for writing programs with powerful, end-to-end security]: Security and Protection--Information flow controls General Terms Languages, Performance , Security Keywords Information flow control, Java virtual machine, oper- ating systems, security region 1. Introduction
A Method for the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.; Whitesides, John L.; Campbell, Richard L.; Mineck, Raymond E.
A fully automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers and airfoil thicknesses. The thrusts of the method are its ability to calculate a target N-Factor distribution that forces the flow to undergo transition at the desired location; the target-pressure-N-Factor relationship that is used to reduce the N-Factors in order to prolong transition; and its ability to design airfoils to meet lift, pitching moment, thickness and leading-edge radius constraints while also being able to meet the natural laminar flow constraint. The method uses several existing CFD codes and can design a new airfoil in only a few days using a Silicon Graphics IRIS workstation.
Thermal transport in laminar flow over superhydrophobic surfaces, utilizing an effective medium approach
NASA Astrophysics Data System (ADS)
Moreira, David; Bandaru, Prabhakar R.
An analytical methodology to characterizing the effects of heat transport in internal laminar flows over ridged patterns, mimicking superhydrophobic surfaces, is indicated. The finite slip velocity on such surfaces and the thermal conductivity characteristics of the constituent material are both shown to modify the convective heat transport in the fluid. We use an effective medium approach to model the lowered thermal conductivity caused by the presence of air in the ridge interstices. The proposed analytical solutions for fully developed flow were verified through comparison with numerical simulations for a periodically ridged geometry in laminar flow. While the convective heat transport and the Nusselt Number (Nu) increase due to the modified fluid velocity profile on superhydrophobic surfaces, the decrease in the thermal conductivity of the substrate may play a larger role in determining the overall heat transfer in the channel.
An adaptive mesh redistribution method for the incompressible mixture flows using phase-field model
NASA Astrophysics Data System (ADS)
Tan, Zhijun; Lim, K. M.; Khoo, B. C.
A phase field model which describes the motion of mixtures of two incompressible fluids is presented by Liu and Shen [C. Liu, J. Shen, A phase field model for the mixture of two incompressible fluids and its approximation by a Fourier-spectral method, Phys. D 179 (2003) 211-228]. The model is based on an energetic variational formulation. In this work, we develop an efficient adaptive mesh method for solving a phase field model for the mixture flow of two incompressible fluids. It is a coupled nonlinear system of Navier-Stokes equations and Allen-Cahn phase equation (phase-field equation) through an extra stress term and the transport term. The numerical strategy is based on the approach proposed by Li et al. [R. Li, T. Tang, P.-W. Zhang, Moving mesh methods in multiple dimensions based on harmonic maps, J. Comput. Phys. 170 (2001) 562-588] to separate the mesh-moving and PDE evolution. In the PDE evolution part, the phase-field equation is numerically solved by a conservative scheme with a Lagrange multiplier, and the coupled incompressible Navier-Stokes equations are solved by the incremental pressure-correction projection scheme based on the semi-staggered grid method. In the mesh-moving part, the mesh points are iteratively redistributed by solving the Euler-Lagrange equations with a parameter-free monitor function. In each iteration, the pressure and the phase are updated on the resulting new grid by a conservative-interpolation formula, while the velocity is re-mapped in a non-conservative approach. A simple method for preserving divergence-free is obtained by projecting the velocity onto the divergence-free space after generating the new mesh at the last iterative step. Numerical experiments are presented to demonstrate the effectiveness of the proposed method for solving the incompressible mixture flows.
Higher-Order Compact Schemes for Numerical Simulation of Incompressible Flows
NASA Technical Reports Server (NTRS)
Wilson, Robert V.; Demuren, Ayodeji O.; Carpenter, Mark
A higher order accurate numerical procedure has been developed for solving incompressible Navier-Stokes equations for 2D or 3D fluid flow problems. It is based on low-storage Runge-Kutta schemes for temporal discretization and fourth and sixth order compact finite-difference schemes for spatial discretization. The particular difficulty of satisfying the divergence-free velocity field required in incompressible fluid flow is resolved by solving a Poisson equation for pressure. It is demonstrated that for consistent global accuracy, it is necessary to employ the same order of accuracy in the discretization of the Poisson equation. Special care is also required to achieve the formal temporal accuracy of the Runge-Kutta schemes. The accuracy of the present procedure is demonstrated by application to several pertinent benchmark problems.
Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media
NASA Astrophysics Data System (ADS)
Liu, Qing; He, Ya-Ling
In this paper, a two-dimensional eight-velocity multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy model. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous matrix are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the incompressible generalized Navier-Stokes equations can be recovered. Numerical simulations of several typical porous flows are carried out to validate the present MRT-LB model. It is found that the present numerical results agree well with the analytical solutions and/or other numerical results reported in the literature.
Steady incompressible potential flow around lifting bodies immersed in a fluid. M.S. Thesis
NASA Technical Reports Server (NTRS)
Chiuchiolo, E. A.
The refinement was investigated of a method for evaluating the pressure distribution on a body surface of arbitrary shape in incompressible flow. The solution was obtained in terms of the velocity potential, through numerical approximations which require the use of a high speed digital computer. The box method and the modal method are described in detail, and were applied to a very thin, rectangular wing in incompressible, steady flow. The box method is found to be more practical as it is applicable to more general geometries (the modal method requires a new set of functions for each geometry), and requires less computer time (fifty percent of that required by the modal method for the same problem).
Advanced natural laminar flow airfoil with high lift to drag ratio
NASA Technical Reports Server (NTRS)
Viken, Jeffrey K.; Pfenninger, Werner; Mcghee, Robert J.
An experimental verification of a high performance natural laminar flow (NLF) airfoil for low speed and high Reynolds number applications was completed in the Langley Low Turbulence Pressure Tunnel (LTPT). Theoretical development allowed for the achievement of 0.70 chord laminar flow on both surfaces by the use of accelerated flow as long as tunnel turbulence did not cause upstream movement of transition with increasing chord Reynolds number. With such a rearward pressure recovery, a concave type deceleration was implemented. Two-dimensional theoretical analysis indicated that a minimum profile drag coefficient of 0.0026 was possible with the desired laminar flow at the design condition. With the three-foot chord two-dimensional model constructed for the LTPT experiment, a minimum profile drag coefficient of 0.0027 was measured at c sub l = 0.41 and Re sub c = 10 x 10 to the 6th power. The low drag bucket was shifted over a considerably large c sub l range by the use of the 12.5 percent chord trailing edge flap. A two-dimensional lift to drag ratio (L/D) was 245. Surprisingly high c sub l max values were obtained for an airfoil of this type. A 0.20 chort split flap with 60 deg deflection was also implemented to verify the airfoil's lift capabilities. A maximum lift coefficient of 2.70 was attained at Reynolds numbers of 3 and 6 million.
Computing three-dimensional incompressible flows with vortex elements
NASA Technical Reports Server (NTRS)
Leonard, A.
The techniques, capabilities and applicability of numerical models of three-dimensional, unsteady vortical flows with high Re are assessed. Vorticity is calculated only in appropriate regions and the velocity field is derived from the boundary conditions. Vorticity is assumed to take the shape of tubes with uniform core structures in the case of turbulence. The efforts being made to simplify equations for dense collections of vortex filaments in order to make them tractable to computer simulations are described. The effectiveness of vorticity arrow representations for accurately describing vorticity fields near surfaces is discussed, along with Lagrangian vortex elements, which may be of use in modelling the rotational part of flows around bluff bodies, nonuniform density flows and chemically reacting flows.
Multigrid Computations of 3-D Incompressible Internal and External Viscous Rotating Flows
NASA Technical Reports Server (NTRS)
Sheng, Chunhua; Taylor, Lafayette K.; Chen, Jen-Ping; Jiang, Min-Yee; Whitfield, David L.
This report presents multigrid methods for solving the 3-D incompressible viscous rotating flows in a NASA low-speed centrifugal compressor and a marine propeller 4119. Numerical formulations are given in both the rotating reference frame and the absolute frame. Comparisons are made for the accuracy, efficiency, and robustness between the steady-state scheme and the time-accurate scheme for simulating viscous rotating flows for complex internal and external flow applications. Prospects for further increase in efficiency and accuracy of unsteady time-accurate computations are discussed.
Incompressible viscous flow computations for the pump components and the artificial heart
NASA Technical Reports Server (NTRS)
Kiris, Cetin
A finite difference, three dimensional incompressible Navier-Stokes formulation to calculate the flow through turbopump components is utilized. The solution method is based on the pseudo compressibility approach and uses an implicit upwind differencing scheme together with the Gauss-Seidel line relaxation method. Both steady and unsteady flow calculations can be performed using the current algorithm. Here, equations are solved in steadily rotating reference frames by using the steady state formulation in order to simulate the flow through a turbopump inducer. Eddy viscosity is computed by using an algebraic mixing-length turbulence model. Numerical results are compared with experimental measurements and a good agreement is found between the two.
An Explicit FEM for 3-D Viscous Incompressible Flows, with a Ebe\\/pcg Iterative Algorithm
U. Gulcat
A numerical procedure for the solution of the 3-D Navier-Stokes equations is developed and implemented for analyzing time-dependent incompressible viscous flows past arbitrary shapes. The equations are discretized using a finite element Galerkjn formulation with a streamwise upwinding option. The discretization in time is performed with fractional steps on the momentum equations to obtain the fractional step velocity field explicitly.
A p-version finite element method for steady incompressible fluid flow and convective heat transfer
NASA Technical Reports Server (NTRS)
Winterscheidt, Daniel L.
A new p-version finite element formulation for steady, incompressible fluid flow and convective heat transfer problems is presented. The steady-state residual equations are obtained by considering a limiting case of the least-squares formulation for the transient problem. The method circumvents the Babuska-Brezzi condition, permitting the use of equal-order interpolation for velocity and pressure, without requiring the use of arbitrary parameters. Numerical results are presented to demonstrate the accuracy and generality of the method.
Performance of Under-resolved Two-Dimensional Incompressible Flow Simulations
David L. Brown; Michael L. Minion
A careful study of the behavior of a Godunov-projection method for the incompressible Navier-Stokes equations as a function of the resolution of the computational mesh is presented. By considering a representative example problem, it is demonstrated that a Godunov-projection method performs as well as an accurate centered finite difference method in cases where the smallest flow scales are well resolved.
An investigation on the incompressible turbulent mean swirling flow characteristics change along straight conical diffuser
M. Benisek; M. Nedeljkovic; S. Cantrak
Energy loss in the swirling flow of an incompressible fluid in a straight conical diffuser is investigated experimentally. The diffuser apparatus has length 1.8 m, inlet diameter 0.4 m, and outlet diameter 0.730 m, and the measurements are obtained at Reynolds numbers between 60,000 and 550,000 and at values of the swirl parameter Omega0 between 0.09 and 2.07. The results
Inapplicability of the dynamic Clark model to the large eddy simulation of incompressible turbulent channel flows
NASA Astrophysics Data System (ADS)
Kobayashi, Hiromichi; Shimomura, Yutaka
The inapplicability of the dynamic Clark model to the large eddy simulation of incompressible turbulent channel flows is proved both analytically and numerically. The reason is neither a negative subgrid-scale eddy viscosity nor an incorrect near-wall scaling, but a negative effective viscosity in the viscous sublayer for the tensor diffusivity term that models the sum of the Leonard and the cross terms.
Multistream Laminar Flow: From a challenge in mixing to membraneless fuel cells and microreactors for cofactor regeneration.
NASA Astrophysics Data System (ADS)
Kenis, Paul
Over the last decade a wide variety of research efforts in microchemical systems, in which fluid flow is laminar, has developed. The original challenge of mixing in the absence of turbulence in this laminar flow regime has been overcome through various technical approaches including zig-zag or serpentine-shaped channels (Branebjerg, Beebe et al.), lamination (e.g. Manz, Jensen et al.), hydrodynamic focusing (Austin et al.), and integrated herringbone features (Stroock et al.). Others have grasped the opportunity to utilize multistream laminar flow for example for a T-sensor for blood analysis (Weigl et al.) and in microfabrication or cell studies (Whitesides et al.). This presentation will highlight the development of (i) a membraneless fuel cell, and (ii) a microreactor for cofactor regeneration that utilize multistream laminar flow. Various performance-determining characteristics and engineering improvements will be discussed.
Experimental Results for a Flapped Natural-laminar-flow Airfoil with High Lift/drag Ratio
NASA Technical Reports Server (NTRS)
Mcghee, R. J.; Viken, J. K.; Pfenninger, W.; Beasley, W. D.; Harvey, W. D.
Experimental results have been obtained for a flapped natural-laminar-flow airfoil, NLF(1)-0414F, in the Langley Low-Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.05 to 0.40 and a chord Reynolds number range from about 3.0 x 10(6) to 22.0 x 10(6). The airfoil was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40, a Reynolds number of 10.0 x 10(6), and a Mach number of 0.40. A 0.125 chord simple flap was incorporated in the design to increase the low-drag, lift-coefficient range. Results were also obtained for a 0.20 chord split-flap deflected 60 deg.
Design of a natural laminar flow wing for a transonic corporate transport
NASA Technical Reports Server (NTRS)
Campbell, R. L.; Waggoner, E. G.; Phillips, P. S.
Two- and three-dimensional computational methods were used to design a wing for a transonic corporate transport that had significant runs of laminar flow on both upper and lower wing surfaces at the cruise condition. The airfoil was derived from a low-speed laminar-flow section. The contour was systematically modified based on results from a two-dimensional transonic code to give favorable pressure gradients to 50-percent chord on the upper surface and 65-percent chord on the lower surface. Three-dimensional transonic codes were used to determine the wing twist and to evaluate the aerodynamic characteristics of the complete configuration at various flight conditions. A leading-edge modification for improved stall characteristics was also designed. The theoretical pressure distributions for the final airfoil correlated well with results from wind-tunnel tests.
Osborne Reynolds' pipe flow: Direct computation from laminar through bypass transition to fully-developed turbulence
NASA Astrophysics Data System (ADS)
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald; Baltzer, Jon; Hickey, Jean-Pierre
The most fundamental internal flow, smooth pipe from a slightly perturbed laminar inlet state continuously through bypass transition to fully-developed turbulence, has been computed using DNS over an axial domain length of 250 pipe radii. In the fully-developed turbulent region, mean and second-order turbulent statistics including the rate of viscous dissipation show excellent agreement with those obtained from an additional simulation using the conventional streamwise periodic boundary condition over an axial domain length of 30 pipe radii. Friction factor follows analytical solution prior to breakdown, and agrees with Moody's correlation after the completion of transition. During transition it exhibits an overshoot. Breakdown of the laminar pipe flow is characterized by the formation of large Lambda-shaped vortices pointing upstream, followed by their subsequent generation of small hairpin packets inclined towards the downstream direction.
Experimental Investigation of a Synthetic Jet Array in a Laminar Channel Flow
NASA Astrophysics Data System (ADS)
Dan?ovß, P.; TrßvnĒ?ek, Z.; VĒt, T.
The paper deals with an impinging synthetic jet, namely on the case of a synthetic jet array interacting with a laminar channel flow. This arrangement can be useful in many micro-scale applications, such as cooling of micro-electronics. The flow regime in micro-scale is usually laminar with very small Reynolds numbers; therefore synthetic jet array can be used for the profile disturbance and heat transfer enhancement. The paper focuses on the low Reynolds number (in order 102). The working fluid is water and a piezoceramic transducer is used as a moving membrane in the synthetic jet actuator. Experiments are performed with four experimental methods (tin ion visualization, hot wire anemometry in constant temperature mode, laser Doppler vibrometry and particle image velocimetry) in three laboratories (at the Eindhoven University of Technology, Netherlands, at the Institute of Thermodynamics CAS, v.v.i. and Technical University of Liberec, both Czech Republic).
An incompressible inner flow analysis by absolute differential form of Navier-Stokes equation on a curvilinear coordinate system
NASA Astrophysics Data System (ADS)
Katsuragi, K.; Ukai, O.
An incompressible inner-flow analysis scheme which is based on the absolute differential form for the conventional equations of the incompressible viscous flow is presented. The physical components of the contravariant vector are taken as velocity variables, and the equations are discretized on a staggered mesh system. Consequently, the calculation is performed stably and the good agreement with the experimental results has been shown in the prediction of the natural convection in the horizontal eccentric cylindrical annuli.
Numerical study of incompressible slightly viscous flow past blunt bodies and airfoils
Cheer, A.Y.L.
A grid free numerical method is used to simulate incompressible flow at high Reynolds number. The numerical method simulates the flow inside the boundary layer by vortex sheets and the flow outside this layer by vortex blobs. The algorithm produces a smooth transition between the sheets and the blobs. The accuracy of this hybrid numerical method is tested in several numerical experiments. In the first experiment, the algorithm is used to simulate slightly viscous flow past a circular cylinder. In the second experiment, the algorithm is used to simulate flow past a Joukowski airfoil at various angles of attack. In the latter case, there is no evidence of blow-up of the flow at the trailing edge of the airfoil. In both experiments, the calculated flow and its functionals (such as lift and drag coefficients) are in good agreement with both theoretical results and wind tunnel experiments.
Unsteady laminar flow and convective heat transfer in a sharp 180░ bend
Yongmann M. Chung; Paul G. Tucker; D. G. Roychowdhury
Unsteady laminar flow and heat transfer in a sharp 180░ bend is studied numerically to investigate a convective heat transfer regime of especial relevance to electronic systems. Due to the high geometrical aspect ratios occurring in the practical application, two-dimensional unsteady simulations are considered. The two-dimensionality assumption adopted is validated by three-dimensional test simulations. Unsteady heat transfer simulations are performed
C. L. Streett
The NASA\\/Boeing hybrid laminar flow control (HLFC) experiment, designed during 1993-1994 and conducted in the NASA LaRC 8-foot Transonic Pressure Tunnel in 1995, utilized computational fluid dynamics and numerical simulation of complex fluid mechanics to an unprecedented extent for the design of the test article and measurement equipment. CFD was used in: the design of the test wing, which was
Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel
William S. Saric
It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in
Development of a compact laminar flow heat exchanger with stainless steel micro-tubes
N. Saji; S. Nagai; K. Tsuchiya; H. Asakura; M. Obata
The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger.We presented in a previous paper that some compact heat exchangers
Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow
Ying Yang; Z. George Zhang; Eric A. Grulke; William B. Anderson; Gefei Wu
The convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger. The nanoparticles used in this research were graphitic in nature, with aspect ratios significantly different from one (l\\/d?0.02). The graphite nanoparticles increased the static thermal conductivities of the fluid significantly at low weight fraction loadings. However, the experimental
Computations of Laminar Flow Control on Swept Wings as a Companion to Flight Test Research
Rhodes, Richard G.
Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved by: Chair of Committee, Helen Reed Committee Members, Jacques Richard Hamn...-Ching Chen Head of Department, Helen Reed December 2008 Major Subject: Aerospace Engineering iii ABSTRACT Computations of Laminar Flow Control on Swept Wings as a Companion to Flight Test Research. (December 2008) Richard George Rhodes, B...
Determination of Kinetic Parameters in Laminar Flow Reactors. II. Experimental Aspects
A. Hanf; H.-R. Volpp; J. Wolfrum
In the present contribution laser spectroscopic studies are described in which the chemical kinetics of benchmark elementary\\u000a reaction steps in different laminar flow reactors were experimentally investigated along with detailed numerical modeling\\u000a calculations (see the article Carraro\\/Heuveline\\/Rannacher [5] in this vol-ume). Coherent anti-Stokes Raman spectroscopy (CARS) was utilized to study the collisional relaxation and vibrational\\u000a energy transfer of vibrationally excited
The Langley 8-ft transonic pressure tunnel laminar-flow-control experiment
NASA Technical Reports Server (NTRS)
Bobbitt, Percy J.; Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.
An account is given of the considerations involved in selecting the NASA-Langley transonic pressure tunnel's design and test parameters, as well as its liner and a swept wing for laminar flow control (LFC) experimentation. Attention is given to the types and locations of the instrumentation employed. Both slotted and perforated upper surfaces were tested with partial- and full-chord suction; representative results are presented for all.
Improved approximate method for simulating frequency-dependent friction in transient laminar flow
Schohl, G.A. (Tennessee Valley Authority, Norris, TN (United States). Engineering Lab.)
A new approximation to the weighting function in Zielke's equation is used in an improved implementation of Trikha's method for including frequency dependent friction in transient laminar flow calculations. The new, five-term approximation was fitted to the weighting function using a nonlinear least squares approach. Transient results obtained using the new approximation function are nearly indistinguishable from results obtained using the exact expression for the weighting function.
The antiinflammatory effect of laminar flow: The role of PPAR, epoxyeicosatrienoic acids, and soluble epoxide hydrolase
Yi Liu; Yingjia Zhang; Kara Schmelzer; Tzong-Shyuan Lee; Xiang Fang; Yi Zhu; Arthur A. Spector; Sarjeet Gill; Christophe Morisseau; Bruce D. Hammock; John Y.-J. Shyy
We previously reported that laminar flow activates peroxisome proliferator-activated receptor (PPAR) in vascular endothelial cells in a ligand-dependent manner that involves phospholipase A2 and cytochrome P450 epoxygenases. In this study, we investigated whether epoxyeicosatrienoic acids (EETs), the catalytic products of cytochrome P450 epoxygenases, are PPAR ligands. Competition and direct binding assays revealed that EETs bind to the ligand-binding domain of
Low-dimensional models for describing mixing effects in laminar flow tubular reactors
Saikat Chakraborty; Vemuri Balakotaiah
The Liapunov¢Schmidt (LS) technique of bifurcation theory is used to average the convective-diffusion equation in the transverse direction and obtain low-dimensional two-mode models that describe mixing effects in laminar flow tubular reactors. For the isothermal case, these models are described by a pair of equations involving two modes, namely, the spatially averaged (?C?) and the mixing-cup (Cm) concentration vectors. The
Rotordynamic characteritics of incompressible-flow labyrinth seals
Ghali, Anupama
and Elrod, 1988), one could easily see the value of the current study to the turbomachinery community. 10 COMPUTATIONAL DEVELOPMENT The axisymmetric flow field, corresponding to the centered-rotor operational mode (Fig. 2), is considered as the first... to the precision of the axisymmetric flow model, or have to do with the very idea on which the perturbation analysis is based. ~OR o A 0 ~ 0 0 LI 'a S S C 0 0 W 0 U z 0 0 0 C4 4I C Tj g nl 0 0 I 4J 4 nl 0 4J (p 0 12 O O I 4J W 0 I 0...
Analysis for the application of hybrid laminar flow control to a long-range subsonic transport aircraft
P. C. Jr. Arcara; D. W. Bartlett; L. A. Mccullers
The FLOPS aircraft conceptual design\\/analysis code has been used to evaluate the effects of incorporating hybrid laminar flow control (HLFC) in a 300-passenger, 6500 n. mi. range, twin-engine subsonic transport aircraft. The baseline configuration was sized to account for 50 percent chord laminar flow on the wing upper surface as well as both surfaces of the empennage airfoils. Attention is
A numerical investigation of laminar and turbulent flow past a cube
Raul, R.
Laminar and turbulent flow past a cube is investigated numerically. A vorticity-vector potential approach is used as the basis for a computational algorithm in which semi-implicit finite difference equations are solved iteratively by a vectorizable 8 color SOR algorithm. The calculations are performed on a CRAY X-MP/48 Supercomputers. The laminar calculations are done at a range of Reynolds numbers from 10 to 100. The predicted drag appear to be in good agreement with relevant data including that from a cube drop experiment performed specifically for the present study. An analysis of the flow structure is made which shows it to be in qualitative agreement with similar flows. The turbulent flow calculations are done at Reynolds numbers of 2,000, 14,000 and 170,000 using the Mean Vorticity and Covariance (MVC) closure. The turbulent flow field is computed down to the solid surface without the use of wall functions. The calculated drag is in good agreement with experimental results. A study of the three-dimensional flow structure is carried out with the help of computer graphics. The flow is observed to separate from the side surfaces of the cube. The calculated axial velocity distribution is shown to be in good agreement with that observed experimentally in similar bluff body flows.
Permeability of ceramic foams to compressible and incompressible flow
E. A. Moreira; M. D. M. Innocentini; J. R. Coury
Ceramic foams constitute a new structural material characterized by a high porosity and high superficial area, formed by megapores interconnected by filaments. This results in a structure with low resistance to fluid flow, and to their use as filter. This work investigates the influence of several structural parameters, such as porosity, tortuosity, surface area and pore diameter, in predicting the
Unified Computational Schemes for Incompressible and Weakly Compressible Flows
Grant, P. W.
between acoustic and convective time-scales. Numerical computation at low Mach number poses a significant;2 SUMMARY A time-marching Taylor-Galerkin finite element algorithm, based on a pressure-correction method compressible flow density interpolation schemes, at low to vanishing Mach number. Primarily, we advocate
A Riemannian geometric mapping technique for identifying incompressible equivalents to subsonic potential flows
NASA Astrophysics Data System (ADS)
German, Brian Joseph
This research develops a technique for the solution of incompressible equivalents to planar steady subsonic potential flows. Riemannian geometric formalism is used to develop a gauge transformation of the length measure followed by a curvilinear coordinate transformation to map the given subsonic flow into a canonical Laplacian flow with the same boundary conditions. The effect of the transformation is to distort both the immersed profile shape and the domain interior nonuniformly as a function of local flow properties. The method represents the full nonlinear generalization of the classical methods of Prandtl-Glauert and Karman-Tsien. Unlike the classical methods which are "corrections," this method gives exact results in the sense that the inverse mapping produces the subsonic full potential solution over the original airfoil, up to numerical accuracy. The motivation for this research was provided by an observed analogy between linear potential flow and the special theory of relativity that emerges from the invariance of the d'Alembert wave equation under Lorentz transformations. This analogy is well known in an operational sense, being leveraged widely in linear unsteady aerodynamics and acoustics, stemming largely from the work of Kussner. Whereas elements of the special theory can be invoked for compressibility effects that are linear and global in nature, the question posed in this work was whether other mathematical techniques from the realm of relativity theory could be used to similar advantage for effects that are nonlinear and local. This line of thought led to a transformation leveraging Riemannian geometric methods common to the general theory of relativity. A gauge transformation is used to geometrize compressibility through the metric tensor of the underlying space to produce an equivalent incompressible flow that lives not on a plane but on a curved surface. In this sense, forces owing to compressibility can be ascribed to the geometry of space in much the same way that general relativity ascribes gravitational forces to the curvature of space-time. Although the analogy with general relativity is fruitful, it is important not to overstate the similarities between compressibility and the physics of gravity, as the interest for this thesis is primarily in the mathematical framework and not physical phenomenology or epistemology. The thesis presents the philosophy and theory for the transformation method followed by a numerical method for practical solutions of equivalent incompressible flows over arbitrary closed profiles. The numerical method employs an iterative approach involving the solution of the equivalent incompressible flow with a panel method, the calculation of the metric tensor for the gauge transformation, and the solution of the curvilinear coordinate mapping to the canonical flow with a finite difference approach for the elliptic boundary value problem. This method is demonstrated for non-circulatory flow over a circular cylinder and both symmetric and lifting flows over a NACA 0012 profile. Results are validated with accepted subcritical full potential test cases available in the literature. For chord-preserving mapping boundary conditions, the results indicate that the equivalent incompressible profiles thicken with Mach number and develop a leading edge droop with increased angle of attack. Two promising areas of potential applicability of the method have been identified. The first is in airfoil inverse design methods leveraging incompressible flow knowledge including heuristics and empirical data for the potential field effects on viscous phenomena such as boundary layer transition and separation. The second is in aerodynamic testing using distorted similarity-scaled models.
Laminar and turbulent flows over spherically blunted cone and hyperboloid with massive surface blowing
NASA Technical Reports Server (NTRS)
Kumar, A.; Twari, S. N.
Numerical solutions are presented for the flow over a spherically blunted cone and hyperboloid with massive surface blowing. Time-dependent viscous shock-layer equations are used to describe the flow field. The boundary conditions on the body surface include a prescribed blowing-rate distribution. The governing equations are solved by a time-asymptotic finite-difference method. Results presented here are only for a perfect gas-type flow at zero angle of attack. Both laminar and turbulent flow solutions are obtained. It is found that the effect of the surface blowing on the laminar flow field is to smooth out the curvature discontinuity at the sphere-cone juncture point, which results in a positive pressure gradient over the body. The shock slope increases on the downstream portion of the body as the surface blowing rate is increased. The turbulent flow with surface blowing is found to redevelop a boundary-layer-like region near the surface. The effects of this boundary-layer region on the flow field and heating rates are discussed.
Pressure Drop of Fully Developed, Laminar Flow in Rough Microtubes
Bahrami, Majid
delivery, physi- cal particle separation, and inkjet print heads. Microchannels can be defined as tubes predicted by conventional theory smooth pipes for liquids in microchannels during the last 15 years see survey articles 1,2 . Tuckerman 3 was the first to experimentally investigate the liquid flow and heat
Multifluid laminar flow in a microchannel (Kenis et al. 1999)
Muradoglu, Metin
reactions, e.g., jet engine and power generation gas turbines, internal combustion engines, furnaces: Micro/biofluidics, multiphase flows, turbulent combustion, CFD. Softwares : We develop and use our in research, we specialize in fluid mechanics, combustion and scientific computing. We're primarily concerned
Stochastic finite difference lattice Boltzmann method for steady incompressible viscous flows
Fu, S.C., E-mail: email@example.com [Mechanical Engineering Department, Hong Kong Polytechnic University, Hung Hom (Hong Kong); So, R.M.C. [Building Services Engineering Department, Hong Kong Polytechnic University, Hung Hom (Hong Kong); Mechanical Engineering Department, Purdue University, West Lafayette, IN 47907 (United States); Leung, W.W.F. [Research Institute of Innovative Products and Technologies, Hong Kong Polytechnic University, Hung Hom (Hong Kong)
With the advent of state-of-the-art computers and their rapid availability, the time is ripe for the development of efficient uncertainty quantification (UQ) methods to reduce the complexity of numerical models used to simulate complicated systems with incomplete knowledge and data. The spectral stochastic finite element method (SSFEM) which is one of the widely used UQ methods, regards uncertainty as generating a new dimension and the solution as dependent on this dimension. A convergent expansion along the new dimension is then sought in terms of the polynomial chaos system, and the coefficients in this representation are determined through a Galerkin approach. This approach provides an accurate representation even when only a small number of terms are used in the spectral expansion; consequently, saving in computational resource can be realized compared to the Monte Carlo (MC) scheme. Recent development of a finite difference lattice Boltzmann method (FDLBM) that provides a convenient algorithm for setting the boundary condition allows the flow of Newtonian and non-Newtonian fluids, with and without external body forces to be simulated with ease. Also, the inherent compressibility effect in the conventional lattice Boltzmann method, which might produce significant errors in some incompressible flow simulations, is eliminated. As such, the FDLBM together with an efficient UQ method can be used to treat incompressible flows with built in uncertainty, such as blood flow in stenosed arteries. The objective of this paper is to develop a stochastic numerical solver for steady incompressible viscous flows by combining the FDLBM with a SSFEM. Validation against MC solutions of channel/Couette, driven cavity, and sudden expansion flows are carried out.
Stochastic finite difference lattice Boltzmann method for steady incompressible viscous flows
NASA Astrophysics Data System (ADS)
Fu, S. C.; So, R. M. C.; Leung, W. W. F.
With the advent of state-of-the-art computers and their rapid availability, the time is ripe for the development of efficient uncertainty quantification (UQ) methods to reduce the complexity of numerical models used to simulate complicated systems with incomplete knowledge and data. The spectral stochastic finite element method (SSFEM) which is one of the widely used UQ methods, regards uncertainty as generating a new dimension and the solution as dependent on this dimension. A convergent expansion along the new dimension is then sought in terms of the polynomial chaos system, and the coefficients in this representation are determined through a Galerkin approach. This approach provides an accurate representation even when only a small number of terms are used in the spectral expansion; consequently, saving in computational resource can be realized compared to the Monte Carlo (MC) scheme. Recent development of a finite difference lattice Boltzmann method (FDLBM) that provides a convenient algorithm for setting the boundary condition allows the flow of Newtonian and non-Newtonian fluids, with and without external body forces to be simulated with ease. Also, the inherent compressibility effect in the conventional lattice Boltzmann method, which might produce significant errors in some incompressible flow simulations, is eliminated. As such, the FDLBM together with an efficient UQ method can be used to treat incompressible flows with built in uncertainty, such as blood flow in stenosed arteries. The objective of this paper is to develop a stochastic numerical solver for steady incompressible viscous flows by combining the FDLBM with a SSFEM. Validation against MC solutions of channel/Couette, driven cavity, and sudden expansion flows are carried out.
Laminar Flow About a Rotating Body of Revolution in an Axial Airstream
NASA Technical Reports Server (NTRS)
Schlichting, H.
We have set ourselves the problem of calculating the laminar flow on a body of revolution in an axial flow which simultaneously rotates about its axis. The problem mentioned above, the flow about a rotating disk in a flow, which we solved some time ago, represents the first step in the calculation of the flow on the rotating body of revolution in a flow insofar as, in the case of a round nose, a small region about the front stagnation point of the body of revolution may be replaced by its tangential plane. In our problem regarding the rotating body of revolution in a flow, for laminar flow, one of the limiting cases is known: that of the body which is in an axial approach flow but does not rotate. The other limiting case, namely the flow in the neighborhood of a body which rotates but is not subjected to a flow is known only for the rotating circular cylinder, aside from the rotating disk. In the case of the cylinder one deals with a distribution of the circumferential velocity according to the law v = omega R(exp 2)/r where R signifies the cylinder radius, r the distance from the center, and omega the angular velocity of the rotation. The velocity distribution as it is produced here by the friction effect is therefore the same as in the neighborhood of a potential vortex. When we treat, in what follows, the general case of the rotating body of revolution in a flow according to the calculation methods of Prandtl's boundary-layer theory, we must keep in mind that this solution cannot contain the limiting case of the body of revolution which only rotates but is not subjected to a flow. However, this is no essential limitation since this case is not of particular importance for practical purposes.
A GPU-accelerated flow solver for incompressible two-phase fluid flows
NASA Astrophysics Data System (ADS)
Codyer, Stephen; Raessi, Mehdi; Khanna, Gaurav
We present a numerical solver for incompressible, immiscible, two-phase fluid flows that is accelerated by using Graphics Processing Units (GPUs). The Navier-Stokes equations are solved by the projection method, which involves solving a pressure Poisson problem at each time step. A second-order discretization of the Poisson problem leads to a sparse matrix with five and seven diagonals for two- and three-dimensional simulations, respectively. Running a serial linear algebra solver on a single CPU can take 50-99.9% of the total simulation time to solve the above system for pressure. To remove this bottleneck, we utilized the large parallelization capabilities of GPUs; we developed a linear algebra solver based on the conjugate gradient iterative method (CGIM) by using CUDA 4.0 libraries and compared its performance with CUSP, an open-source, GPU library for linear algebra. Compared to running the CGIM solver on a single CPU core, for a 2D case, our GPU solver yields speedups of up to 88x in solver time and 81x overall time on a single GPU card. In 3D cases, the speedups are up to 81x (solver) and 15x (overall). Speedup is faster at higher grid resolutions and our GPU solver outperforms CUSP. Current work examines the acceleration versus a parallel CGIM CPU solver.
Iterative and multigrid methods in the finite element solution of incompressible and turbulent fluid flow
NASA Astrophysics Data System (ADS)
Lavery, N.; Taylor, C.
Multigrid and iterative methods are used to reduce the solution time of the matrix equations which arise from the finite element (FE) discretisation of the time-independent equations of motion of the incompressible fluid in turbulent motion. Incompressible flow is solved by using the method of reduce interpolation for the pressure to satisfy the Brezzi-Babuska condition. The k-l model is used to complete the turbulence closure problem. The non-symmetric iterative matrix methods examined are the methods of least squares conjugate gradient (LSCG), biconjugate gradient (BCG), conjugate gradient squared (CGS), and the biconjugate gradient squared stabilised (BCGSTAB). The multigrid algorithm applied is based on the FAS algorithm of Brandt, and uses two and three levels of grids with a V-cycling schedule. These methods are all compared to the non-symmetric frontal solver. Copyright
Time-accurate incompressible flow computations with quadrilateral velocity-pressure elements
NASA Technical Reports Server (NTRS)
Tezduyar, T. E.; Mittal, S.; Shih, R.
Quadrilateral velocity-pressure elements with constant and linear pressure interpolations are examined in the context of time-accurate finite element computation of unsteady incompressible flows. These elements involve streamline-upwind/Petrov-Galerkin stabilization and are implemented in conjunction with the one-step and multi-step temporal integration of the Navier-Stokes equations. The two test cases chosen for the performance evaluation of the formulations are the standing vortex problem and flow past a circular cylinder at Reynolds number 100.
A pressure based method for the solution of viscous incompressible turbomachinery flows
NASA Technical Reports Server (NTRS)
Hobson, Garth Victor; Lakshminarayana, B.
A new technique was developed for the solution of the incompressible Navier-Stokes equations. The numerical technique, derived from a pressure substitution method (PSM), overcomes many of the deficiencies of the pressure correction method. This technique allows for the direct solution of the actual pressure in the form of a Poisson equation which is derived from the pressure weighted substitution of the full momentum equations into the continuity equation. Two dimensional internal flows are computed with this method. The prediction of cascade performance is presented. The extention of the pressure correction method for the solution of three dimensional flows is also presented.
Goal-oriented model adaptivity for viscous incompressible flows
NASA Astrophysics Data System (ADS)
van Opstal, T. M.; Bauman, P. T.; Prudhomme, S.; van Brummelen, E. H.
In van Opstal et al. (Comput Mech 50:779-788, 2012) airbag inflation simulations were performed where the flow was approximated by Stokes flow. Inside the intricately folded initial geometry the Stokes assumption is argued to hold. This linearity assumption leads to a boundary-integral representation, the key to bypassing mesh generation and remeshing. It therefore enables very large displacements with near-contact. However, such a coarse assumption cannot hold throughout the domain, where it breaks down one needs to revert to the original model. The present work formalizes this idea. A model adaptive approach is proposed, in which the coarse model (a Stokes boundary-integral equation) is locally replaced by the original high-fidelity model (Navier-Stokes) based on a-posteriori estimates of the error in a quantity of interest. This adaptive modeling framework aims at taking away the burden and heuristics of manually partitioning the domain while providing new insight into the physics. We elucidate how challenges pertaining to model disparity can be addressed. Essentially, the solution in the interior of the coarse model domain is reconstructed as a post-processing step. We furthermore present a two-dimensional numerical experiments to show that the error estimator is reliable.
Adaptive time-step with anisotropic meshing for incompressible flows
NASA Astrophysics Data System (ADS)
Coupez, T.; Jannoun, G.; Nassif, N.; Nguyen, H. C.; Digonnet, H.; Hachem, E.
This paper presents a method of combining anisotropic mesh adaptation and adaptive time-stepping for Computational Fluid Dynamics (CFD). First, we recall important features of the anisotropic meshing approach using a posteriori estimates relying on the length distribution tensor approach and the associated edge based error analysis. Then we extend the proposed technique to contain adaptive time advancing based on a newly developed time error estimator. The objective of this paper is to show that the combination of time and space anisotropic adaptations with highly stretched elements can be used to compute high Reynolds number flows within reasonable computational and storage costs. In particular, it will be shown that boundary layers, flow detachments and all vortices are well captured automatically by the mesh. The time-step is controlled by the interpolation error and preserves the accuracy of the mesh adapted solution. A Variational MultiScale (VMS) method is employed for the discretization of the Navier-Stokes equations. Numerical solutions of some benchmark problems demonstrate the applicability of the proposed space-time error estimator. An important feature of the proposed method is its conceptual and computational simplicity as it only requires from the user a number of nodes according to which the mesh and the time-steps are automatically adapted.
Pore-scale simulation of laminar flow through porous media
NASA Astrophysics Data System (ADS)
Piller, M.; Casagrande, D.; Schena, G.; Santini, M.
The experimental investigation of flow through porous media is inherently difficult due to the lack of optical access. The recent developments in the fields of X-ray micro-tomography (micro-CT hereafter), digital sample reconstruction by image-processing techniques and fluid-dynamics simulation, together with the increasing power of super-computers, allow to carry out pore-scale simulations through digitally-reconstructed porous samples. The scientific relevance of pore-scale simulations lies in the possibility of upscaling the pore-level data, yielding volume-averaged quantities useful for practical purposes. One of the best-known examples of upscaling is the calculation of absolute and relative permeability of reservoir rocks. This contribution presents a complete work-flow for setting up pore-scale simulations, starting from the micro-CT of a (in general small) porous sample. Relevant applications are discussed in order to reveal the potential of the proposed methodology.
Two experimental supercritical laminar-flow-control swept-wing airfoils
NASA Technical Reports Server (NTRS)
Allison, Dennis O.; Dagenhart, J. Ray
Two supercritical laminar-flow-control airfoils were designed for a large-chord swept-wing experiment in the Langley 8-Foot Transonic Pressure Tunnel where suction was provided through most of the model surface for boundary-layer control. The first airfoil was derived from an existing full-chord laminar airfoil by extending the trailing edge and making changes in the two lower-surface concave regions. The second airfoil differed from the first one in that it was designed for testing without suction in the forward concave region of the lower surface. Differences between the first airfoil and the one from which it was derived as well as between the first and second airfoils are discussed. Airfoil coordinates and predicted pressure distributions for the design normal Mach number of 0.755 and section lift coefficient of 0.55 are given for the three airfoils.
A unified method for the numerical analysis of compressible and incompressible viscous flows
NASA Astrophysics Data System (ADS)
Nonaka, N.; Nakayama, T.
A new unified numerical method is presented for the analysis of both compressible and incompressible viscous flows. The proposed method has two key features. One is the energy equation expressed in terms of pressure. The other is the description of the governing equations in non-conservative forms. The both features contribute greatly to the construction of the computational method. The temporal discretization of the governing equations are based on the finite difference method. The procedure for advancing flow field variables in a time step consists of two phases, namely an advection phase and a non-advection phase, and accordingly the governing equations are split into the advection and non-advection equations. First, the non-advection phase is calculated. The non-advection equations are discretized in space by using the Galerkin FEM. Those discrete equations are solved in an implicit manner to yield the intermediate values of the variables. These intermediate values are corrected by solving the advection equations. The advection equations derived from the momentum equations are discretized in space by the SU/PG-FEM, while the advection equations from the continuity and the energy equations are discretized by the finite volume method with a first-order upwinding scheme. The proposed method is demonstrated on four numerical examples of compressible and incompressible flows; a shock-tube problem, a supersonic flow over a forward-facing step, incompressible flows over a backward-facing step and in a lid-driven cavity. The accuracy of the proposed method has been assessed by comparing our numerical results with other numerical results, analytical solutions and available experimental data. Stable and accurate computations have been attained.
On Analysis of Stationary Viscous Incompressible Flow Through a Radial Blade Machine
NASA Astrophysics Data System (ADS)
Neustupa, TomßÜ
The paper is concerned with the analysis of the two dimensional model of incompressible, viscous, stationary flow through a radial blade machine. This type of turbine is sometimes called Kaplan's turbine. In the technical area the use is either to force some regular characteristic to the flow of the medium going through the turbine (flow of melted iron, air conditioning) or to gain some energy from the flowing medium (water). The inflow and outflow part of boundary are in general a concentric circles. The larger one represents an inflow part of boundary the smaller one the outflow part of boundary. Between them are regularly spaced the blades of the machine. We study the existence of the weak solution in the case of nonlinear boundary condition of the "do-nothing" type. The model is interesting for study the behavior of the flow when the boundary is formed by mutually disjoint and separated parts.
A parallel overset-curvilinear-immersed boundary framework for simulating complex 3D incompressible flows
Borazjani, Iman; Ge, Liang; Le, Trung; Sotiropoulos, Fotis
We develop an overset-curvilinear immersed boundary (overset-CURVIB) method in a general non-inertial frame of reference to simulate a wide range of challenging biological flow problems. The method incorporates overset-curvilinear grids to efficiently handle multi-connected geometries and increase the resolution locally near immersed boundaries. Complex bodies undergoing arbitrarily large deformations may be embedded within the overset-curvilinear background grid and treated as sharp interfaces using the curvilinear immersed boundary (CURVIB) method (Ge and Sotiropoulos, Journal of Computational Physics, 2007). The incompressible flow equations are formulated in a general non-inertial frame of reference to enhance the overall versatility and efficiency of the numerical approach. Efficient search algorithms to identify areas requiring blanking, donor cells, and interpolation coefficients for constructing the boundary conditions at grid interfaces of the overset grid are developed and implemented using efficient parallel computing communication strategies to transfer information among sub-domains. The governing equations are discretized using a second-order accurate finite-volume approach and integrated in time via an efficient fractional-step method. Various strategies for ensuring globally conservative interpolation at grid interfaces suitable for incompressible flow fractional step methods are implemented and evaluated. The method is verified and validated against experimental data, and its capabilities are demonstrated by simulating the flow past multiple aquatic swimmers and the systolic flow in an anatomic left ventricle with a mechanical heart valve implanted in the aortic position. PMID:23833331
High-order ALE schemes for incompressible capillary flows
NASA Astrophysics Data System (ADS)
Montefuscolo, Felipe; Sousa, Fabricio S.; Buscaglia, Gustavo C.
The spatial discretization of problems with moving boundaries is considered, incorporating the temporal evolution of not just the mechanical variables, but also of the nodal positions of the moving mesh. The outcome is a system of Differential-Algebraic Equations (DAE) of index 2 or, in the case of inertialess flow, just 1. From the DAE formulation it its possible to define strategies to build schemes of arbitrary accuracy. We introduce here several schemes of order 2 and 3 that avoid the solution of a nonlinear system involving simultaneously the mechanical variables and the geometrical ones. This class of schemes has been the one adopted by the majority of practitioners of Computational Fluid Dynamics up to now. The proposed schemes indeed achieve the design accuracy, and further show stability restrictions that are not significantly more severe than those of popular first order schemes. The numerical experimentation is performed on capillary problems, discretized by both div-stable (P2/P1, P1+/P1) and equal-order (P1/P1, stabilized) finite elements, and incorporating surface tension and triple (contact) line effects.
Notes on Newton-Krylov based Incompressible Flow Projection Solver
Robert Nourgaliev; Mark Christon; J. Bakosi
The purpose of the present document is to formulate Jacobian-free Newton-Krylov algorithm for approximate projection method used in Hydra-TH code. Hydra-TH is developed by Los Alamos National Laboratory (LANL) under the auspices of the Consortium for Advanced Simulation of Light-Water Reactors (CASL) for thermal-hydraulics applications ranging from grid-to-rod fretting (GTRF) to multiphase flow subcooled boiling. Currently, Hydra-TH is based on the semi-implicit projection method, which provides an excellent platform for simulation of transient single-phase thermalhydraulics problems. This algorithm however is not efficient when applied for very slow or steady-state problems, as well as for highly nonlinear multiphase problems relevant to nuclear reactor thermalhydraulics with boiling and condensation. These applications require fully-implicit tightly-coupling algorithms. The major technical contribution of the present report is the formulation of fully-implicit projection algorithm which will fulfill this purpose. This includes the definition of non-linear residuals used for GMRES-based linear iterations, as well as physics-based preconditioning techniques.
A new fully explicit algorithm for incompressible flows
NASA Astrophysics Data System (ADS)
Park, Sangro; Lee, Changhoon
The Poisson equation for pressure arising from nonzero divergence of the nonlinear term in the integration of the Navier-Stokes equations requires a lot of computational cost except for cases with periodic domain. In order to mitigate this cost, we propose a new project algorithm which is fully explicit, thus not requiring iterations. The projection operator, 1 -?i?j /?2 , which projects any vector field with divergence into the divergence-free subspace in the Fourier space, when transformed into the physical space, shows decaying distribution with the distance from the point in question. This allows truncation so that the resulting local distribution of the projection operator, through convolution, can be used to obtain projected nonlinear terms which has relatively small divergence. This ``approximate'' projection scheme was then applied to direct numerical simulation of isotropic turbulence to investigate effectiveness and efficiency of the scheme in reducing divergence and correct projection of the nonlinear terms through the statistical properties of the turbulent flow. Performance of the scheme in a variety of aspects is investigated and details will be presented in the meeting.
Experimental study on laminar flow forced-convection in a channel with upper V-corrugated plate heated by radiation
Ahmed Hamza H Ali; Yutaka Hanaoka
Experimental study of the effects of the operating parameters on laminar flow forced-convection heat transfer for air flowing in a channel having a V-corrugated upper plate heated by radiation heat flux while the other walls are thermally insulated has been carried out. The parameters studied and their ranges were as follows: flow Reynolds number (Re) ranging from 750 to 2050,
A numerical study of fully developed laminar flows in pipes with two planar curvatures
NASA Astrophysics Data System (ADS)
Niewiadomski, C.; Paraschivoiu, M.; Sullivan, P.
The spectral element method is applied on unstructured tetrahedral elements to solve the Navier-Stokes equations for fully developed laminar flow in pipes with two planar curvatures. Specific implementations of the spectral element method to double curved pipes and parallelization are described. Previous studies on flows in pipes focused on constant curvature or torsion geometries, as well as pipes with varying curvature. This study focuses on the periodic variation of both the curvature as well as torsion by analysing a pipe having two planar curvatures. The effects of the three parameters defining the pipe are studied to isolate the curvature and torsion effect on the magnitude and angle of the secondary flow. Furthermore, the geometric effects on the wall shear stress are studied, as it is an important fluid flow property, especially in blood flows.
The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves
NASA Technical Reports Server (NTRS)
Duck, Peter W.
The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.
Computational Analysis of a Laminar Jet in a Cross-Flow
NASA Technical Reports Server (NTRS)
Jeffries, Damon K.; Krishnamurthy, R.; Chandra, S.
A jet in cross-flow (JIFC) consists of a jet exhausting at a large angle into a freestream flow. It is a flow field which is relevant to a wide variety of technologies and applications. Despite the nearly 65 years of JIFC research there are few results available for laminar hypersonic flows, a combination which will be encountered by re-entry and high altitude vehicles over some portion of their flight path. This research consists of developing a numerical model to investigate the interaction of a normal sonic jet exhausting into a hypersonic cross-flow. The model was validated by comparing experimental measurements with corresponding numerical results generated by the model.
Distinct large-scale turbulent-laminar states in transitional pipe flow
Moxey, David; Barkley, Dwight
When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar motion and complex turbulent motion. The discontinuous transition between these states is a fundamental problem that has been studied for more than 100Āyr. What has received far less attention is the large-scale nature of the turbulent flows near transition once they are established. We have carried out extensive numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transitional turbulence in pipe flow. We show the existence of three fundamentally different turbulent states separated by two distinct Reynolds numbers. Below ReĀ1Ā?Ā2,300, turbulence takes the form of familiar equilibrium (or longtime transient) puffs that are spatially localized and keep their size independent of pipe length. At ReĀ1 the flow makes a striking transition to a spatio-temporally intermittent flow that fills the pipe. Irregular alternation of turbulent and laminar regions is inherent and does not result from random disturbances. The fraction of turbulence increases with Re until ReĀ2Ā?Ā2,600 where there is a continuous transition to a state of uniform turbulence along the pipe. We relate these observations to directed percolation and argue that ReĀ1 marks the onset of infinite-lifetime turbulence. PMID:20404193
An experimental study on the efficiency of transpiration cooling in laminar and turbulent hypersonic flows
NASA Astrophysics Data System (ADS)
G³lhan, A.; Braun, S.
An experimental study on the efficiency of transpiration cooling in hypersonic laminar and turbulent flow regimes is carried out in the Hypersonic Windtunnel Cologne with a focus on the aerothermal problems downstream of the cooled model part. The model is made of a material of low thermal conductivity (PEEK) with an integrated probe of a porous material. The experimental setup allows the direct comparison of the thermal behavior of transpiration cooling to a well-defined and radiatively cooled reference surface. Experiments are performed at Mach number of 6 and two different Reynolds numbers. Air, argon and helium are used as coolants at various flow rates, in order to identify the influence of coolant medium on cooling efficiency. The cooling efficiency of air and argon is comparable. Helium provides significantly higher cooling efficiency at the same blowing ratio, i.e. same coolant mass flow rate. The experimental data shows that the efficiency of the transpiration cooling in turbulent flows is much lower than in laminar flow.
Numerical investigation of laminar flow and heat transfer in a radial flow cooling system with the use of nanofluids
Gilles Roy; Cong Tam Nguyen; Paul-Renķ Lajoie
Nanofluids, because of their enhanced heat transfer capability as compared to normal water\\/glycol\\/oil based fluids, offer the engineer opportunities for development in areas where high heat transfer, low temperature tolerance and small component size are required. In this present paper, the hydrodynamic and thermal fields of a water¢?Al2O3 nanofluid in a radial laminar flow cooling system are considered. Results indicate
Cauchy's almost forgotten Lagrangian formulation of the Euler equation for 3D incompressible flow
NASA Astrophysics Data System (ADS)
Frisch, Uriel; Villone, Barbara
Two prized papers, one by Augustin Cauchy in 1815, presented to the French Academy and the other by Hermann Hankel in 1861, presented to G÷ttingen University, contain major discoveries on vorticity dynamics whose impact is now quickly increasing. Cauchy found a Lagrangian formulation of 3D ideal incompressible flow in terms of three invariants that generalize to three dimensions the now well-known law of conservation of vorticity along fluid particle trajectories for two-dimensional flow. This has very recently been used to prove analyticity in time of fluid particle trajectories for 3D incompressible Euler flow and can be extended to compressible flow, in particular to cosmological dark matter. Hankel showed that Cauchy's formulation gives a very simple Lagrangian derivation of the Helmholtz vorticity-flux invariants and, in the middle of the proof, derived an intermediate result which is the conservation of the circulation of the velocity around a closed contour moving with the fluid. This circulation theorem was to be rediscovered independently by William Thomson (Kelvin) in 1869. Cauchy's invariants were only occasionally cited in the 19th century - besides Hankel, foremost by George Stokes and Maurice Lķvy - and even less so in the 20th until they were rediscovered via Emmy Noether's theorem in the late 1960, but reattributed to Cauchy only at the end of the 20th century by Russian scientists.
Effective equations describing the flow of a viscous incompressible fluid through a long elastic tube
NASA Astrophysics Data System (ADS)
?ani?, Sun?ica; Mikeli?, Andro
We study the flow of a viscous incompressible fluid through a long and narrow elastic tube whose walls are modeled by the Navier equations for a curved, linearly elastic membrane. The flow is governed by a given small time dependent pressure drop between the inlet and the outlet boundary, giving rise to creeping flow modeled by the Stokes equations. By employing asymptotic analysis in thin, elastic, domains we obtain the reduced equations which correspond to a Biot type viscoelastic equation for the effective pressure and the effective displacement. The approximation is rigorously justified by obtaining the error estimates for the velocity, pressure and displacement. Applications of the model problem include blood flow in small arteries. We recover the well-known Law of Laplace and provide a new, improved model when shear modulus of the vessel wall is not negligible. To cite this article: S. ?ani?, A. Mikeli?, C. R. Mecanique 330 (2002) 661-666.
Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids
NASA Technical Reports Server (NTRS)
Anderson, W. Kyle; Rausch, Russ D.; Bonhaus, Daryl L.
An implicit code for computing inviscid and viscous incompressible flows on unstructured grids is described. The foundation of the code is a backward Euler time discretization for which the linear system is approximately solved at each time step with either a point implicit method or a preconditioned Generalized Minimal Residual (GMRES) technique. For the GMRES calculations, several techniques are investigated for forming the matrix-vector product. Convergence acceleration is achieved through a multigrid scheme that uses non-nested coarse grids that are generated using a technique described in the present paper. Convergence characteristics are investigated and results are compared with an exact solution for the inviscid flow over a four-element airfoil. Viscous results, which are compared with experimental data, include the turbulent flow over a NACA 4412 airfoil, a three-element airfoil for which Mach number effects are investigated, and three-dimensional flow over a wing with a partial-span flap.
Complex fluid dynamics: From laminar to geophysical flows
NASA Astrophysics Data System (ADS)
Veysey, John J., II
In this dissertation, we present analytical, experimental, and numerical work relating to two problems in fluid flow. We first treat the oldest, hardest, and arguably one of the most important problems in boundary layer theory: determining the drag on a sphere and an infinite cylinder moving at a fixed speed in a highly viscous fluid. We necessarily extensively review previous experimental and theoretical work, and then apply techniques based on the perturbative renormalization group to produce optimal "coarse-grained" approximations. These approximations lead to a new prediction for the drag coefficient, one which both reproduces and surpasses the results of matched asymptotics. We next present investigations into the biocomplex system at Yellowstone National Park. This research, which includes field work, experimental measurements, and numerical modelling, has shown that microbes do not play an important role in the formation of large scale carbonate terraces. Although we found that microbial communities are highly correlated with depositional facies, we demonstrated that this is a consequence of tight correlations between aqueous chemistry and the underlying travertine. We show how these correlations can be used to reconstruct ancient depositional environments. We also present highly successful minimal models which explain the formation of depositional facies and large scale travertine motifs, including the characteristic terrace architecture found at carbonate hot springs. Our numerical model predicts dynamical phenomena which are seen at real hot springs. It also produces patterns which have the same static statistical properties as those seen at real hot springs, and indicates that hot spring terraces are indeed scale invariant; we show that the distribution of pond areas in both simulated landscapes and real hot springs obeys the same power law. By analogy with studies of vicinal surfaces, we identify another universal statistical characterization, the terrace width distribution. We present evidence from both simulated landscapes and experimental data that this distribution is a universal property of carbonate terraces, applying regardless of the details of local chemistry and biology.
Stability of the laminar boundary-layer flow behind a roughness element
NASA Astrophysics Data System (ADS)
Shin, Yong-su; Rist, Ulrich; Krõmer, Ewald
Roughness elements in laminar boundary layers generate both high shear layers and streaky structures. Because these phenomena interact, it is difficult to precisely ascertain the dominant instability mechanisms. With the goal of explicating such interactions, we study the stability of a laminar boundary layer subject to a single roughness element at a Reynolds number subcritical of bypass transition. Our work involves two parts: bi-global linear stability theory (LST) analysis and corroborating experimental measurements. Linear stability analysis of a flat-plate boundary layer perturbed by streamwise streaks reveals the presence of several unstable modes. Of the dominant two modes, one exhibits spanwise symmetry and the other is antisymmetric. These modes are termed `varicose' and `sinuous,' respectively. Corroborating experiments were conducted in the laminar water channel of the University of Stuttgart. By simultaneously traversing two hot-film probes, we are able to confirm the presence of both eigenmodes predicted by LST and to extract relevant data for each: eigenvalues, eigenfunctions, growth rates and phase distributions. The main part of the experiments has been performed under `natural' conditions, i.e., in the absence of external forcing. As the amplitude of the sinuous part of the results is much smaller than the varicose one and hence affected by measurement noise, a case with asymmetric external forcing is presented as well. Despite some deficiencies of the setup, it is possible to enhance the sinuous mode with respect to the unforced case and to confirm its existence as an eigenmode of the flow.
Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow
Rolland, Joran
This article is concerned with the numerical study and modelling of two aspects the formation of laminar holes in transitional turbulence of plane Couette flow (PCF). On the one hand, we consider quenches: sudden decreases of the Reynolds number R which force the formation of holes. The Reynolds number is decreased from featureless turbulence to the range of existence of the oblique laminar-turbulent bands [Rg;Rt]. The successive stages of the quench are studied by means of visualisations and measurements of kinetic energy and turbulent fraction. The behaviour of the kinetic energy is explained using a kinetic energy budget: it shows that viscosity causes quasi modal decay until lift-up equals it and creates a new balance. Moreover, the budget confirms that the physical mechanisms at play are independent of the way the quench is performed. On the other hand we consider the natural formation of laminar holes in the bands, near Rg. The Direct Numerical simulations (DNS) show that holes in the turbulent bands pr...
Development of a compact laminar flow heat exchanger with stainless steel micro-tubes
NASA Astrophysics Data System (ADS)
Saji, N.; Nagai, S.; Tsuchiya, K.; Asakura, H.; Obata, M.
The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger. We presented in a previous paper that some compact heat exchangers with good performance in the temperature range of less than 4 K are required for a subcooled He II refrigerator cycle to be worked with 3He turbo-compressors (F. Doty, et al., A new look at the closed brayton cycle, Proceedings, IECEC-90 Reno, NV, 1991, p. 116). For this requirement, we developed a micro-tube strip counter flow type heat exchanger, which consists of 12 elements with a total of 4800 stainless steel micro-tubes. Each element is formed with 400 tubes and a newly developed vacuum brazing method was applied for the bonding to the side plate. Each tube has an inner diameter of 0.5 mm, an outer diameter of 0.7 mm and is 310 mm long. We developed a cladding plate with two layers of gold brazing sheet sandwiched inside. In aerodynamic and thermal design of the element, the laminar flow conditions were adopted for the flows of inner and outer tubes to keep a high heat transfer rate and a low pressure loss.
Moderated, Water-Based, Condensational Particle Growth in a Laminar Flow
Hering, Susanne V.; Spielman, Steven R.; Lewis, Gregory S.
Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30░C in the majority of the flow and providing an exiting dew point below 15░C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The ōmoderatedö approach presented here replaces this warm region with a two sections ¢ a short, warm, wet-walled ōinitiatorö, followed by a cool-walled ōmoderatorö. The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling. PMID:24839342
Effect of varied air flow on flame structure of laminar inverse diffusion flames.
Shaddix, Christopher R.; Williams, Timothy C.; Blevins, Linda Gail; Mikofski, Mark A. (University of California Berkeley)
The structure of laminar inverse diffusion flames (IDFs) of methane and ethylene was studied using a cylindrical co-flowing burner. Several flames of the same fuel flow-rate yet various air flow-rates were examined. Heights of visible flames were obtained using measurements of hydroxyl (OH) laser-induced fluorescence (LIF) and visible images. Polycyclic aromatic hydrocarbon (PAH) LIF and soot laser-induced incandescence (LII) were also measured. In visible images, radiating soot masks the blue region typically associated with the flame height in normal diffusion flames (NDFs). Increased air flow-rates resulted in longer flames. PAH LIF and soot LII indicated that PAh and soot are present on the fuel side of the flame and that soot is located closer to the reaction zone than PAH. Ethylene flames produced significantly higher PAH LIF and soot LII signals than methane flames, which is consistent with the sooting propensity of ethylene.
Active control of instabilities in laminar boundary-layer flow. Part 1: An overview
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.; Erlebacher, Gordon; Hussaini, M. Yousuff
This paper (the first in a series) focuses on using active-control methods to maintain laminar flow in a region of the flow in which the natural instabilities, if left unattended, lead to turbulent flow. The authors review previous studies that examine wave cancellation (currently the most prominent method) and solve the unsteady, nonlinear Navier-Stokes equations to evaluate this method of controlling instabilities. It is definitely shown that instabilities are controlled by the linear summation of waves (i.e., wave cancellation). Although a mathematically complete method for controlling arbitrary instabilities has been developed (but not yet tested), the review, duplication, and physical explanation of previous studies are important steps for providing an independent verification of those studies, for establishing a framework for subsequent work which will involve automated transition control, and for detailing the phenomena by which the automated studies can be used to expand knowledge of flow control.
A continuous-flow C. elegans sorting system with integrated optical fiber detection and laminar flow switching.
Yan, Yuanjun; Ng, Li Fang; Ng, Li Theng; Choi, Kwan Bum; Gruber, Jan; Bettiol, Andrew A; Thakor, Nitish V
We present a high-throughput continuous-flow C. elegans sorting device that works based on integrated optical fiber detection and laminar flow switching. Two types of genetically engineered nematodes are allowed to flow into the device and their genotypes are detected based on their fluorescence, without the need for immobilization, by integrated optical fibers. A novel dynamic fluidic switch sorts the nematodes to desired outlets. By changing input pressures of the control inlets, the laminar flow path is altered to steer the nematodes to appropriate outlets. Compared to previously reported microfluidic C. elegans sorting devices, sorting in this system is conducted in a continuous flow environment without any immobilization technique or need for multilayer mechanical valves to open and close the outlets. The continuous flow sorter not only increases the throughput but also avoids any kind of invasive or possibly damaging mechanical or chemical stimulus. We have characterized both the detection and the switching accuracy of the sorting device at different flow rates, and efficiencies approaching 100% can be achieved with a high throughput of about one nematode per second. To confirm that there was no significant damage to C. elegans following sorting, we recovered the sorted worms, finding no deaths and no differences in behavior and propagation compared to control. PMID:25140819
A general explicit or semi-explicit algorithm for compressible and incompressible flows
NASA Technical Reports Server (NTRS)
Zienkiewicz, O. C.; Wu, J.
A unified finite element algorithm is developed which is applicable to a wide range of problems of fluid mechanics without recourse to artificial, empirically determined factors. In its explicit form, the algorithm is similar to the Taylor-Galerkin scheme and is easily adopted to standard codes. The scheme proposed here possesses sufficient natural balancing diffusion and thus reduces and sometimes eliminates the need for special 'shock capturing' diffusion. The efficiency of the algorithm is demonstrated using several examples ranging from incompressible through transonic regions to supersonic flows.
A spectral multi-domain technique applied to stability and transition of incompressible and compressible flows
NASA Technical Reports Server (NTRS)
Macaraeg, Michele; Streett, Craig L.
Techniques for the numerical simulation of compressible and incompressible viscous flows are described and demonstrated. The focus is on a multidomain spectral method based on the flux-balance domain-interface scheme of Macaraeg and Streett (1986). The fundamental principles of the method are reviewed, and it is shown that the multidomain spectral approach facilitates the treatment of instability and the transition to turbulence. Typical numerical results for the Taylor-Couette problem and for bounded compressible high-speed mixing layers are presented in graphs and briefly characterized.
A Level Set Approach for Computing Solutions to Incompressible Two-Phase Flow
NASA Astrophysics Data System (ADS)
Sussman, Mark; Smereka, Peter; Osher, Stanley
A level set approach for computing solutions to incompressible two-phase flow is presented. The interface between the two fluids is considered to be sharp and is described as the zero level set of a smooth function. We use a second-order projection method which implements a second-order upwinded procedure for differencing the convection terms. A new treatment of the level set method allows us to include large density and viscosity ratios as well as surface tension. We consider the motion of air bubbles in water and falling water drops in air.
An adaptive pressure correction method without spurious velocities for diffuse-interface models of incompressible flows
NASA Astrophysics Data System (ADS)
Minjeaud, Sebastian
In this article, we propose to study two issues associated with the use of the incremental projection method for solving the incompressible Navier-Stokes equation. The first one is the combination of this time splitting algorithm with an adaptive local refinement method. The second one is the reduction of spurious velocities due to the right-hand side of the momentum balance. We propose a new variant of the incremental projection method for solving the Navier-Stokes equations with variable density and illustrate its behavior with the example of two phase flows simulations using a Cahn-Hilliard/Navier-Stokes model.
A Multiblock Approach for Calculating Incompressible Fluid Flows on Unstructured Grids
NASA Technical Reports Server (NTRS)
Sheng, Chunhua; Whitfield, David L.; Anderson, W. Kyle
A multiblock approach is presented for solving two-dimensional incompressible turbulent flows on unstructured grids. The artificial compressibility form of the governing equations is solved by a vertex-centered, finite-volume implicit scheme which uses a backward Euler time discretization. Point Gauss-Seidel relaxations are used to solve the linear system of equations at each time step. This work introduces a multiblock strategy to the solution procedure, which greatly improves the efficiency of the algorithm by significantly reducing the memory requirements while not increasing the CPU time. Results presented in this work shows that the current multiblock algorithm requires 70% less memory than the single block algorithm.
3-D laser Doppler velocimetry study of incompressible flow through an orifice plateĀ
Panak, David Leo
) Ken Kihm (Member) Kenneth Hall (Member) alter Bradley (Head of Department) May 1990 3-D Laser Doppler Velocimetry Study of Incompressible Flow Through an Orifice Plate. (May 1990) David Leo Panak, B. S. , Texas A&M University Chair... Velocimetry 3-D Laser Doppler Velocimeter . LDV Signal Generation and Processing VITA Page 33 34 37 37 38 42 48 50 56 56 57 58 59 61 69 69 72 76 81 LIST OF FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Beveled orifice meter plate, P...
Natural laminar flow data from full-scale flight and wind-tunnel experiments
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Coy, P. F.; Yip, L. P.; Brown, P. W.; Obara, C. J.
Experimental results obtained at NASA Langley during studies of natural laminar flow (NLF) over commercially produced aircraft surfaces are reported. The general aviation aircraft examined were light aircraft, yet displayed NLF extents close to the maximum available and equivalent to high performance business aircraft flying envelopes. Sublimating chemicals and acoustic detection techniques were employed to measure the boundary layer transition. Theoretical predictions of boundary layer stability were found to match well with the experimental data, with consideration given to both swept wings and the amplitudes of allowable waves on the airfoil surfaces. The presence of the NLF on the airfoil surfaces confirmed the benefits available from use of composite materials for airfoil surfaces.
Design and experimental results for a flapped natural-laminar-flow airfoil for general aviation applications
NASA Technical Reports Server (NTRS)
Somers, D. M.
A flapped natural laminar flow airfoil for general aviation applications, the NLF(1)-0215F, has been designed and analyzed theoretically and verified experimentally in the Langley Low Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low speed airfoils with the low cruise drag of the NACA 6 series airfoils has been achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge has also been met. Comparisons of the theoretical and experimental results show generally good agreement.
Validation of the Natural-Laminar-Flow Design for the National Experimental Supersonic Transport
NASA Astrophysics Data System (ADS)
Nomura, Toshiyuki; Kuroda, Fumitake
The natural-laminar-flow (NLF) design for the wing of the national experimental supersonic transport (NEXST) aims to suppress crossflow (CF) instability near the leading edge. We computationally investigate the growth of various stationary CF disturbances on the outer wing of the NEXST-1 model using the prediction system of boundary-layer transition. According to the N factors obtained, the growth of those disturbances is completely suppressed around the designed angle of attack, which shows that the NLF design for the NEXST-1 wing is valid.
Opportunities for applications of natural laminar flow technology at high-subsonic speeds
NASA Technical Reports Server (NTRS)
Viken, Jeff; Pfenninger, W.; Wagner, R. D.; Collier, F. S., Jr.
The possible profiles of high subsonic speed airfoils with extensive regions of natural laminar flow (NLF) are explored, on the bases of calculations which suggest that high subsonic Mach number NLFs are obtainable for both swept and unswept wing applications at certain Reynolds numbers. Attention is given to the transonic pressure distributions of airfoils for unswept wings at freestream Mach numbers of 0.65-0.80 and chord Reynolds numbers of up to 50 million. The case of 10-30 deg swept-wing NLF airfoils is also investigated for chord Reynolds numbers of 15-50 million.
Natural laminar flow airfoil design considerations for winglets on low-speed airplanes
NASA Technical Reports Server (NTRS)
Vandam, C. P.
Winglet airfoil section characteristics which significantly influence cruise performance and handling qualities of an airplane are discussed. A good winglet design requires an airfoil section with a low cruise drag coefficient, a high maximum lift coefficient, and a gradual and steady movement of the boundary layer transition location with angle of attack. The first design requirement provides a low crossover lift coefficient of airplane drag polars with winglets off and on. The other requirements prevent nonlinear changes in airplane lateral/directional stability and control characteristics. These requirements are considered in the design of a natural laminar flow airfoil section for winglet applications and chord Reynolds number of 1 to 4 million.
Effects of an aft facing step on the surface of a laminar flow glider wing
NASA Technical Reports Server (NTRS)
Sandlin, Doral R.; Saiki, Neal
A motor glider was used to perform a flight test study on the effects of aft facing steps in a laminar boundary layer. This study focuses on two dimensional aft facing steps oriented spanwise to the flow. The size and location of the aft facing steps were varied in order to determine the critical size that will force premature transition. Transition over a step was found to be primarily a function of Reynolds number based on step height. Both of the step height Reynolds numbers for premature and full transition were determined. A hot film anemometry system was used to detect transition.
Infection prevention for patients with acute leukemia using laminar air flow rooms.
Masaoka, T
Infection prevention using laminar air flow (LAF) rooms was studied. For the effective and economical usage of LAF rooms, our trials with ozone decontamination were deemed very convenient and effective. In maintaining LAF clean, insects were found to be a critical factor regarding fungus contamination of LAF. As to its efficacy of infection prevention, LAF decreased infection during remission induction from 113/100 to 28/100. The infections reduced by LAF were pneumonia, upper respiratory infection and skin abscess, while sepsis and perianal infection were not affected. Treatment in LAF rooms also seemed to have comparable influence on interstitial pneumonitis after bone marrow transplantation. PMID:2837838
Unique laminar-flow stability limit based shallow-water theory
Chen, Cheng-lung
Two approaches are generally taken in deriving the stability limit for the Froude member (Fs) for laminar sheet flow. The first approach used the Orr-Sommerfeld equation, while the second uses the cross-section-averaged equations of continuity and motion. Because both approaches are based on shallow-water theory, the values of Fs obtained from both approaches should be identical, yet in the literature they are not. This suggests that a defect exists in at least one of the two approaches. After examining the governing equations used in both approaches, one finds that the existing cross-section -averaged equation of motion is dependent on the frame of reference.
Prediction of Laminar and Turbulent Boundary Layer Flow Separation in V/STOL Engine Inlets
NASA Technical Reports Server (NTRS)
Chou, D. C.; Luidens, R. W.; Stockman, N. O.
A description is presented of the development of the boundary layer on the lip and diffuser surface of a subsonic inlet at arbitrary operating conditions of mass flow rate, free stream velocity and incidence angle. Both laminar separation on the lip and turbulent separation in the diffuser are discussed. The agreement of the theoretical results with model experimental data illustrates the capability of the theory to predict separation. The effects of throat Mach number, inlet size, and surface roughness on boundary layer development and separation are illustrated.
Petrov-Galerkin finite element stabilization for two-phase flows
NASA Astrophysics Data System (ADS)
Giordano, Michele; Magi, Vinicio
A finite element model for incompressible laminar two-phase flows is presented. A two-fluid model, describing the laminar non-equilibrium flow of two incompressible phases, is discretized by means of a properly designed streamline upwind Petrov-Galerkin (SUPG) finite element procedure. Such a procedure is consistent with a continuous pressure equation. The design and the implementation of the algorithm are presented together with its validation throughout a comparison with simulations available in the literature.
Viscid-inviscid interaction associated with incompressible flow past wedges at high Reynolds number
NASA Technical Reports Server (NTRS)
Warpinski, N. R.; Chow, W. L.
An analytical method is suggested for the study of the viscid inviscid interaction associated with incompressible flow past wedges with arbitrary angles. It is shown that the determination of the nearly constant pressure (base pressure) prevailing within the near wake is really the heart of the problem, and the pressure can only be established from these interactive considerations. The basic free streamline flow field is established through two discrete parameters which adequately describe the inviscid flow around the body and the wake. The viscous flow processes such as the boundary layer buildup, turbulent jet mixing, and recompression are individually analyzed and attached to the inviscid flow in the sense of the boundary layer concept. The interaction between the viscous and inviscid streams is properly displayed by the fact that the aforementioned discrete parameters needed for the inviscid flow are determined by the viscous flow condition at the point of reattachment. It is found that the reattachment point behaves as a saddle point singularity for the system of equations describing the recompressive viscous flow processes, and this behavior is exploited for the establishment of the overall flow field. Detailed results such as the base pressure, pressure distributions on the wedge, and the geometry of the wake are determined as functions of the wedge angle.
Direct primitive variable incompressible solutions for two and three dimensional viscous flows
NASA Astrophysics Data System (ADS)
Kaushik, S.; Rubin, S. G.; Khosla, P. K.
Two new primitive variable formulations for incompressible viscous flows are described and validated for a variety of 2D and 3D flows. The first fully implicit formulation is based on a box scheme for the primitive variables including velocity, vorticity, and a modified Bernoulli or total pressure. This formulation which is applied to only 2D flows does not require the vorticity transport equation. The second formulation is based on a semiimplicit, time marching method for standard primitive variables. All linear terms are treated implicitly and nonlinear convection terms are treated explicitly. For both schemes the discrete continuity equation is satisfied directly at each time step without artificial compressibility or pressure Poisson concepts.
Numerical studies of incompressible flow around delta and double-delta wings
NASA Technical Reports Server (NTRS)
Krause, E.; Liu, C. H.
The subject has been jointly investigated at NASA Langley Research Center and the Aerodynamisches Institut of the RWTH Aachen over a substantial period. The aim of this investigation has been to develop numerical integration procedures for the Navier-Stokes equations - particularly for incompressible three-dimensional viscous flows about simple and double delta wings - and to study the low speed flow behavior, with its complex vortex structures on the leeward side of the wing. The low speed flight regime poses unusual problems because high incidence flight conditions may, for example, encounter symmetric and asymmetric vortex breakdown. Because of the many difficulties to be expected in solving the problem, it was divided into two - analysis of the flow without vortex breakdown and analysis of the breakdown of isolated vortices. The major results obtained so far on the two topics are briefly described.
A Quadrilateral Spectral Multidomain Penalty Method Model For High Reynolds Number Incompressible Stratified Flows
NASA Astrophysics Data System (ADS)
Escobar-Vargas, Jorge; Diamessis, Peter
We present a spectral multidomain penalty method-based incompressible Navier Stokes solver for high Reynolds number stratified turbulent flows in doubly non-periodic domains. Within the solver, time is discretized with a fractional-step method, and, in space, a Gauss-Lobatto-Legendre collocation approach is used in discontinuous quadrilateral subdomains. Stability of the numerical scheme is guaranteed through a penalty scheme and spectral filtering, further buttressed by a overintegration-based dealiasing technique. The efficient iterative solution of the associated discrete pressure Poisson equation is ensured through a Kronecker product based computation of the null vector associated with the global matrix, plus a two-level preconditioner within a GMRES solver. Efficiency and accuracy of the Navier Stokes solver are assessed through the solution of the lid-driven cavity flow, Taylor vortex and double shear layer. The canonical lock exchange problem is also presented to assess the potential of the solver for the study of environmental stratified flows.
A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow
NASA Technical Reports Server (NTRS)
Weinan, E.; Shu, Chi-Wang
High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved.
A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow
NASA Technical Reports Server (NTRS)
Weinan, E.; Shu, Chi-Wang
High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.
Status report on a natural laminar-flow nacelle flight experiment
NASA Technical Reports Server (NTRS)
Hastings, Earl C., Jr.; Faust, G. K.; Mungur, Parma; Obara, Clifford J.; Dodbele, S. S.; Schoenster, James A.; Jones, Michael G.
The natural laminar flow (NLF) nacelle experiment is part of a drag reduction production program, and has the dual objectives of studying the extent of NLF on full scale nacelles in a flight environment and the effect of acoustic disturbance on the location of transition on the nacelle surface. The experiment is being conducted in two phases: (1) an NLF fairing was flown on a full scale Citation nacelle to develop the experiment technique and establish feasibility; (2) full scale, flow through, NLF nacelles located below the right wing of an experimental NASA OV-1 aircraft are evaluated. The measurements of most interest are the static pressure distribution and transition location on the nacelle surface, and the fluctuating pressure levels associated with the noise sources. Data are collected in combinations of acoustic frequencies and sound pressure levels. The results of phase 2 tests to date indicate that on shape GE2, natural laminar flow was maintained as far aft as the afterbody joint at 50 percent of the nacelle length. An aft facing step at this joint caused premature transition at this station. No change was observed in the transition pattern when the noise sources were operated.
A finite element computational method for high Reynolds number laminar flows
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables are interpolated using complete quadratic shape functions, and the pressure is interpolated using linear shape functions which are defined on a triangular element for the two-dimensional case and on a tetrahedral element for the three-dimensional case. The triangular element and the tetrahedral element are contained inside the complete bi- and tri-quadratic elements for velocity variables for two and three dimensional cases, respectively, so that the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow of Reynolds numbers 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorably with the finite difference computational results and/or experimental data available. It was found that the present method can capture the delicate pressure driven recirculation zones, that the method did not yield any spurious pressure modes, and that the method requires fewer grid points than the finite difference methods to obtain comparable computational results.
Development of high-lift laminar wing using steady active flow control
NASA Astrophysics Data System (ADS)
Clayton, Patrick J.
Fuel costs represent a large fraction of aircraft operating costs. Increased aircraft fuel efficiency is thus desirable. Laminar airfoils have the advantage of reduced cruise drag and increased fuel efficiency. Unfortunately, they cannot perform adequately during high-lift situations (i.e. takeoff and landing) due to low stall angles and low maximum lift caused by flow separation. Active flow control has shown the ability to prevent or mitigate separation effects, and increase maximum lift. This fact makes AFC technology a fitting solution for improving high-lift systems and reducing the need for slats and flap elements. This study focused on experimentally investigating the effects of steady active flow control from three slots, located at 1%, 10%, and 80% chord, respectively, over a laminar airfoil with 45 degree deflected flap. A 30-inch-span airfoil model was designed, fabricated, and then tested in the Bill James 2.5'x3' Wind Tunnel at Iowa State University. Pressure data were collected along the mid-span of the airfoil, and lift and drag were calculated. Five test cases with varying injection locations and varying C? were chosen: baseline, blown flap, leading edge blowing, equal blowing, and unequal blowing. Of these cases, unequal blowing achieved the greatest lift enhancement over the baseline. All cases were able to increase lift; however, gains were less than anticipated.
Three-dimensional measurement of the laminar flow field inside a static mixer
NASA Astrophysics Data System (ADS)
Speetjens, Michel; Jilisen, Rene; Bloemen, Paul
Static mixers are widely used in industry for laminar mixing of viscous fluids as e.g. polymers and food stuffs. Moreover, given the similarities in flow regime, static mixers often serve as model for compact mixers for process intensification and even for micro-mixers. This practical relevance has motivated a host of studies on the mixing characteristics of static mixers and their small-scale counterparts. However, these studies are primarily theoretical and numerical. Experimental studies, in contrast, are relatively rare and typically restricted to local 2D flow characteristics or integral quantities (pressure drop, residence-time distributions). The current study concerns 3D measurements on the laminar flow field inside a static mixer using 3D Particle-Tracking Velocimetry (3D-PTV) Key challenges to the 3D-PTV image-processing procedure are the optical distortion and degradation of the particle imagery due to light refraction and reflection caused by the cylindrical boundary and the internal elements. Ways to tackle these challenges are discussed and first successful 3D measurements in an actual industrial static mixer are presented.
Laminar boundary layer on cone in supersonic flow at large angle of attack
NASA Technical Reports Server (NTRS)
Moore, Franklin K
The laminar boundary-layer flow about a circular cone at large angles of attack to a supersonic stream has been analyzed in the plane of symmetry by a method applicable in general to the flow about conical bodies. At the bottom of the cone, velocity profiles were obtained showing the expected tendency of the boundary layer to become thinner on the under side of the cone as the angle of attack is increased. At the top of the cone, the analysis failed to yield unique solutions except for small angles of attack. Beyond a certain critical angle of attack, boundary-layer flow does not exist in the plane of symmetry, thus indicating separation. This critical angle is presented as a function of Mach number and cone vertex angle.
Adaptive finite element analysis of hypersonic laminar flows for aerothermal load predictions
NASA Technical Reports Server (NTRS)
Ramakrishnan, R.; Thornton, E. A.; Wieting, A. R.
The use of an adaptive mesh refinement procedure for analyzing hypersonic laminar flows with application to aerothermal load predictions is described. The adaptation procedure, which uses both quadrilateral and triangular elements, is implemented with the multistep Galerkin-Runge-Kutta scheme. Elements that lie in regions of strong gradients are refined based on indicators to obtain better definition of flow features. The effectiveness of the adaptive procedure is demonstrated by modeling Mach 11.7 flow over a 15-deg ramp. Numerical results are compared with predictions of strong interaction theories and experimental data. Surface quantities such as heating rates and pressure loads, critical for the effective design of high-speed vehicles, are found to be in good agreement with experimental values.
Application of Hybrid Laminar Flow Control to Global Range Military Transport Aircraft
NASA Technical Reports Server (NTRS)
Lange, Roy H.
A study was conducted to evaluate the application of hybrid laminar flow control (HLFC) to global range military transport aircraft. The global mission included the capability to transport 132,500 pounds of payload 6500 nautical miles, land and deliver the payload and without refueling return 6500 nautical miles to a friendly airbase. The preliminary design studies show significant performance benefits obtained for the HLFC aircraft as compared to counterpart turbulent flow aircraft. The study results at M=0.77 show that the largest benefits of HLFC are obtained with a high wing with engines on the wing configuration. As compared with the turbulent flow baseline aircraft, the high wing HLFC aircraft shows 17 percent reduction in fuel burned, 19.2 percent increase in lift-to-drag ratio, an insignificant increase in operating weight, and a 7.4 percent reduction in gross weight.
Attenuation of Sinusoidal Perturbations Superimposed on Laminar Flow of a Liquid in a Long Line
NASA Technical Reports Server (NTRS)
Holland, Carl M.; Blade, Robert J.; Dorsch, Robert G.
The attenuation constant for sinusoidal pressure and flow perturbations superimposed on the laminar flow of a viscous liquid was measured in a system consisting of a long, straight, cylindrical hydraulic line. The upstream and downstream ends of the line were securely fastened t o the ground. A sinusoidal perturbation was imposed on the mean flow at the upstream end by means of a s m a l l oscillation of a throttle valve abmt a partly open mean position. The downstream end was terminated in a restricting orifice. Pressure perturbations were measured at three locations along the line for frequencies from 15 t o 100 cps. These pressure measurements were reduced by use of a pair of complex damped acoustic one-dimensional wave equations to obtain the attenuation constant along with the phase constant and the dimensionless downstream admittance. For the range of frequencies investigated, the experimental values of the attenuation constant are in good agreement with classical theory.
Laminar-turbulent patterning in wall-bounded shear flows: a Galerkin model
NASA Astrophysics Data System (ADS)
Seshasayanan, K.; Manneville, P.
On its way to turbulence, plane Couette flow¢the flow between counter-translating parallel plates¢displays a puzzling steady oblique laminar-turbulent pattern. We approach this problem via Galerkin modelling of the Navier¢Stokes equations. The wall-normal dependence of the hydrodynamic field is treated by means of expansions on functional bases fitting the boundary conditions exactly. This yields a set of partial differential equations for spatiotemporal dynamics in the plane of the flow. Truncating this set beyond the lowest nontrivial order is numerically shown to produce the expected pattern, therefore improving over what was obtained at the cruder effective wall-normal resolution. Perspectives opened by this approach are discussed.
Dispersion in cylindrical channels on the laminar flow at low Fourier numbers.
Kucza, Witold; D?browa, Juliusz; Nawara, Katarzyna
A numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg-Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90)ū10(-9)m(2)s(-1), respectively, agree well with the literature data. PMID:26041524
An adaptive level set approach for incompressible two-phase flows
Sussman, M.; Almgren, A.S.; Bell, J.B. [and others
In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth function; this has the effect of replacing the advection of density, which has steep gradients at the interface, with the advection of the level set function, which is smooth. In addition, the interface can merge or break up with no special treatment. The authors maintain the level set function as the signed distance from the interface in order to robustly compute flows with high density ratios and stiff surface tension effects. In this work, they couple the level set scheme to an adaptive projection method for the incompressible Navier-Stokes equations, in order to achieve higher resolution of the interface with a minimum of additional expense. They present two-dimensional axisymmetric and fully three-dimensional results of air bubble and water drop computations.
Identification of whistling ability of a single hole orifice from an incompressible flow simulation
Lacombe, Romain; Moussou, Pierre [LaMSID - UMR EDF/CNRS/CEA, DEN-DM2S, 8193 EDF R et D, 1 avenue du General de Gaulle, 92141 Clamart Cedex (France); Auregan, Yves [Universite du Maine, Le Mans, (France)
Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number; the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced. (authors)
Analysis for the application of hybrid laminar flow control to a long-range subsonic transport aircraft
NASA Technical Reports Server (NTRS)
Arcara, P. C., Jr.; Bartlett, D. W.; Mccullers, L. A.
The FLOPS aircraft conceptual design/analysis code has been used to evaluate the effects of incorporating hybrid laminar flow control (HLFC) in a 300-passenger, 6500 n. mi. range, twin-engine subsonic transport aircraft. The baseline configuration was sized to account for 50 percent chord laminar flow on the wing upper surface as well as both surfaces of the empennage airfoils. Attention is given to the additional benefits of achieving various degrees of laminar flow on the engine nacelles, and the horsepower extraction and initial weight and cost increments entailed by the HLFC system. The sensitivity of the results obtained to fuel-price and off-design range are also noted.
An arrayed hot-film sensor for detection of laminar boundary-layer flow disturbance spatial characteristics
NASA Technical Reports Server (NTRS)
Wusk, M. S.; Carraway, D. L.; Holmes, B. J.
An arrayed hot-film sensor has been developed for use in laminar boundary-layer research for the detection of crossflow or Goertler vortices. This sensor has been developed to detect spatial variations in heat transfer which are characteristic of crossflow or Goertler vortices. The sensor is ultimately intended for flight research applications. This paper describes the sensor, its priciples of operation, signal analysis techniques, and experimental results illustrating the spatial detection capabilities of this specialized hot-film device. Discretely placed spheres placed in the boundary layer created alternating regions of undisturbed and disturbed laminar flow over a prototype sensor. Flow visualization results were correlated with the sensor output to demonstrate the ability of the sensor to determine the spatial boundaries of localized disturbances in laminar flow. This work represents the initial steps toward the validation and calibration of an arrayed hot-film sensor for the detection of crossflow or Goertler vorticity wavelength and/or wave frequency.
A combined PHREEQC-2/parallel fracture model for the simulation of laminar/non-laminar flow and contaminant transport with reactions.
Masciopinto, Costantino; Volpe, Angela; Palmiotta, Domenico; Cherubini, Claudia
A combination of a parallel fracture model with the PHREEQC-2 geochemical model was developed to simulate sequential flow and chemical transport with reactions in fractured media where both laminar and turbulent flows occur. The integration of non-laminar flow resistances in one model produced relevant effects on water flow velocities, thus improving model prediction capabilities on contaminant transport. The proposed conceptual model consists of 3D rock-blocks, separated by horizontal bedding plane fractures with variable apertures. Particle tracking solved the transport equations for conservative compounds and provided input for PHREEQC-2. For each cluster of contaminant pathways, PHREEQC-2 determined the concentration for mass-transfer, sorption/desorption, ion exchange, mineral dissolution/precipitation and biodegradation, under kinetically controlled reactive processes of equilibrated chemical species. Field tests have been performed for the code verification. As an example, the combined model has been applied to a contaminated fractured aquifer of southern Italy in order to simulate the phenol transport. The code correctly fitted the field available data and also predicted a possible rapid depletion of phenols as a result of an increased biodegradation rate induced by a simulated artificial injection of nitrates, upgradient to the sources. PMID:20701994
Data Analysis for the NASA/Boeing Hybrid Laminar Flow Control Crossflow Experiment
NASA Technical Reports Server (NTRS)
Eppink, Jenna L.; Wlezien, Richard
The Hybrid-Laminar Flow Control (HLFC) Crossflow Experiment, completed in 1995. generated a large database of boundary layer stability and transition data that was only partially analyzed before data analysis was abruptly ended in the late 1990's. Renewed interest in laminar flow technologies prompted additional data analysis, to integrate all data, including some post-test roughness and porosity measurements. The objective is to gain new insights into the effects of suction on boundary layer stability. A number of challenges were encountered during the data analysis, and their solutions are discussed in detail. They include the effect of the probe vibration, the effect of the time-varying surface temperature on traveling crossflow instabilities, and the effect of the stationary crossflow modes on the approximation of wall location. Despite the low turbulence intensity of the wind tunnel (0.01 to 0.02%), traveling crosflow disturbances were present in the data, in some cases at amplitudes up to 1% of the freestream velocity. However, the data suggests that transition was dominated by stationary crossflow. Traveling crossflow results and stationary data in the presence of suction are compared with linear parabolized stability equations results as a way of testing the quality of the results.
Certification aspects of airplanes which may operate with significant natural laminar flow
NASA Technical Reports Server (NTRS)
Gabriel, Edward A.; Tankesley, Earsa L.
Recent research by NASA indicates that extensive natural laminar flow (NLF) is attainable on modern high performance airplanes currently under development. Modern airframe construction methods and materials, such as milled aluminum skins, bonded aluminum skins, and composite materials, offer the potential for production of aerodynamic surfaces having waviness and roughness below the values which are critical for boundary layer transition. Areas of concern with the certification aspects of Natural Laminar Flow (NLF) are identified to stimulate thought and discussion of the possible problems. During its development, consideration has been given to the recent research information available on several small business and experimental airplanes and the certification and operating rules for general aviation airplanes. The certification considerations discussed are generally applicable to both large and small airplanes. However, from the information available at this time, researchers expect more extensive NLF on small airplanes because of their lower operating Reynolds numbers and cleaner leading edges (due to lack of leading-edge high lift devices). Further, the use of composite materials for aerodynamic surfaces, which will permit incorporation of NLF technology, is currently beginning to appear in small airplanes.
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong T.
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Analysis of Low Speed Stall Aerodynamics of a Swept Wing with Laminar Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong T.
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft s swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First AIAA CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Analytical solutions of heat transfer for laminar flow in rectangular channels
NASA Astrophysics Data System (ADS)
Rybi?ski, Witold; Mikielewicz, Jaros?aw
The paper presents two analytical solutions namely for Fanning friction factor and for Nusselt number of fully developed laminar fluid flow in straight mini channels with rectangular cross-section. This type of channels is common in mini- and microchannel heat exchangers. Analytical formulae, both for velocity and temperature profiles, were obtained in the explicit form of two terms. The first term is an asymptotic solution of laminar flow between parallel plates. The second one is a rapidly convergent series. This series becomes zero as the cross-section aspect ratio goes to infinity. This clear mathematical form is also inherited by the formulae for friction factor and Nusselt number. As the boundary conditions for velocity and temperature profiles no-slip and peripherally constant temperature with axially constant heat flux were assumed (H1 type). The velocity profile is assumed to be independent of the temperature profile. The assumption of constant temperature at the channel's perimeter is related to the asymptotic case of channel's wall thermal resistance: infinite in the axial direction and zero in the peripheral one. It represents typical conditions in a minichannel heat exchanger made of metal.
Flutter control of incompressible flow turbomachine blade rows by splitter blades
NASA Technical Reports Server (NTRS)
Chiang, Hsiao-Wei D.; Fleeter, Sanford
Splitter blades as a passive flutter control technique is investigated by developing a mathematical model to predict the stability of an aerodynamically loaded splittered-rotor operating in an incompressible flow field. The splitter blades, positioned circumferentially in the flow passage between two principal blades, introduce aerodynamic and/or combined aerodynamic-structural detuning into the rotor. The two-dimensional oscillating cascade unsteady aerodynamics, including steady loading effects, are determined by developing a complete first-order unsteady aerodynamic analysis together with an unsteady aerodynamic influence coefficient technique. The torsion mode flutter of both uniformly spaced tuned rotors and detuned rotors are predicted by incorporating the unsteady aerodyamic influence coefficients into a single-degree-of-freedom aeroelastic model. This model is then utilized to demonstrate that incorporating splitters into unstable rotor configurations results in stable splittered-rotor configurations.
A High Order Discontinuous Galerkin Method for 2D Incompressible Flows
NASA Technical Reports Server (NTRS)
Liu, Jia-Guo; Shu, Chi-Wang
In this paper we introduce a high order discontinuous Galerkin method for two dimensional incompressible flow in vorticity streamfunction formulation. The momentum equation is treated explicitly, utilizing the efficiency of the discontinuous Galerkin method The streamfunction is obtained by a standard Poisson solver using continuous finite elements. There is a natural matching between these two finite element spaces, since the normal component of the velocity field is continuous across element boundaries. This allows for a correct upwinding gluing in the discontinuous Galerkin framework, while still maintaining total energy conservation with no numerical dissipation and total enstrophy stability The method is suitable for inviscid or high Reynolds number flows. Optimal error estimates are proven and verified by numerical experiments.
A Multigrid Accelerated High-Order Compact Fractional Step Method for Unsteady Incompressible Viscous Flows
NASA Astrophysics Data System (ADS)
San, Omer; Staples, Anne
An efficient high-order compact scheme is presented for computing unsteady incompressible viscous flows. The scheme is constructed on a staggered Cartesian grid. Using the fractional step framework, the Navier-Stokes equations are advanced in time with the second-order Adams-Bashforth method without considering the pressure terms in the predictor step. The velocity field is then corrected so that the continuity equation is satisfied through a pressure Poisson equation. Since the efficiency of the fractional step method depends on the Poisson solver, a Mehrstellen-based V-cycle multigrid acceleration is implemented in the solution of the Poisson equation to enhance the computational efficiency. The method is validated by simulating a decaying Taylor-Green vortex. The results show that the method has high resolving efficiency, drastically reduced computational time, and high-order accuracy, making it applicable for the simulation of complex turbulent flows.
Numerical simulation of unsteady incompressible viscous flows in generalized coordinate systems
NASA Technical Reports Server (NTRS)
Rossenfeld, Moshe; Kwak, Dochan
Several numerical solutions of the three-dimensional unsteady incompressible Navier-Stokes equations in generalized coordinate systems are presented. The governing equations are discretized by finite volumes with special care to the accurate approximation of the geometric quantities. The unknowns are the pressure and the volume fluxes over the computational cell faces. This formulation results in a robust fractional step solution method for solving discrete equations. Although this method is formulated for the three-dimensional case, only two-dimensional unsteady results are given. Results are presented for a lid driven two-dimensional cavity flow at Reynolds number of 10,000 and for the flow over a circular cylinder with vortex shedding for several Reynolds numbers in the range 100 less than Re less than 1000.
Numerical simulation of unsteady incompressible viscous flows in generalized coordinate systems
NASA Technical Reports Server (NTRS)
Rosenfeld, Moshe; Kwak, Dochan
Several numerical solutions of the three dimensional unsteady incompressible Navier-Stokes equations in generalized coordinate systems are presented. The governing equations are discretized by finite volumes with special care to the accurate approximation of the geometric quantities. The unknowns are the pressure and the volume fluxes over the computational cell faces. This formulation results in a robust fractional step solution method for solving discrete equations. Although this method is formulated for the three dimensional case, only two dimensional unsteady results are given. Results are presented for a lid driven two dimensional cavity flow at Reynolds number of 10,000, and for the flow over a circular cylinder with vortex shedding for several Reynolds numbers in the range 100 less than Re less than 1000.
A computer program for calculating laminar and turbulent boundary layers for two-dimensional time-dependent flows
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
A computer program is described which provides solutions of two dimensional equations appropriate to laminar and turbulent boundary layers for boundary conditions with an external flow which fluctuates in magnitude. The program is based on the numerical solution of the governing boundary layer equations by an efficient two point finite difference method. An eddy viscosity formulation was used to model the Reynolds shear stress term. The main features of the method are briefly described and instructions for the computer program with a listing are provided. Sample calculations to demonstrate its usage and capabilities for laminar and turbulent unsteady boundary layers with an external flow which fluctuated in magnitude are presented.
Experimental study of the laminar-turbulent transition of a concave wall in a parallel flow
NASA Technical Reports Server (NTRS)
Bippes, H.
The instability of the laminar boundary layer flow along a concave wall was studied. Observations of these three-dimensional boundary layer phenomena were made using the hydrogen-bubble visualization technique. With the application of stereo-photogrammetric methods in the air-water system it was possible to investigate the flow processes qualitatively and quantitatively. In the case of a concave wall of sufficient curvature, a primary instability occurs first in the form of Goertler vortices with wave lengths depending upon the boundary layer thickness and the wall curvature. At the onset the amplification rate is in agreement with the linear theory. Later, during the non-linear amplification stage, periodic spanwise vorticity concentrations develop in the low velocity region between the longitudinal vortices. Then a meandering motion of the longitudinal vortex streets subsequently ensues, leading to turbulence.
The development and evaluation of advanced technology laminar-flow-control subsonic transport aircraft
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
A study was conducted to evaluate the technical and economic feasibility of applying laminar flow control (LFC) to the wings and empennage of long-range subsonic transport aircraft for initial operation in 1985. For a design mission range of 5500 n mi, advanced technology LFC and turbulent-flow aircraft were developed for a 200-passenger payload, and compared on the basis of production costs, direct operating costs, and fuel efficiency. Parametric analyses were conducted to establish optimum geometry, advanced system concepts were evaluated, and configuration variations maximizing the effectiveness of LFC were developed. The final comparisons include consideation of maintenance costs and procedures, manufacturing costs and procedures, and operational considerations peculiar to LFC aircraft.
Lubricant-impregnated surfaces for drag reduction in viscous laminar flow
NASA Astrophysics Data System (ADS)
Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team
For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).
Base pressure associated with incompressible flow past wedges at high Reynolds numbers
NASA Technical Reports Server (NTRS)
Warpinski, N. R.; Chow, W. L.
A model is suggested to study the viscid-inviscid interaction associated with steady incompressible flow past wedges of arbitrary angles. It is shown from this analysis that the determination of the nearly constant pressure (base pressure) prevailing within the near wake is really the heart of the problem and this pressure can only be determined from these interactive considerations. The basic free streamline flow field is established through two discrete parameters which should adequately describe the inviscid flow around the body and the wake. The viscous flow processes such as boundary-layer buildup along the wedge surface, jet mixing, recompression, and reattachment which occurs along the region attached to the inviscid flow in the sense of the boundary-layer concept, serve to determine the aforementioned parameters needed for the establishment of the inviscid flow. It is found that the point of reattachment behaves as a saddle point singularity for the system of equations describing the viscous recompression process. Detailed results such as the base pressure, pressure distributions on the wedge surface, and the wake geometry as well as the influence of the characteristic Reynolds number are obtained. Discussion of these results and their comparison with the experimental data are reported.
Multiphase lattice Boltzmann flux solver for incompressible multiphase flows with large density ratio
NASA Astrophysics Data System (ADS)
Wang, Y.; Shu, C.; Huang, H. B.; Teo, C. J.
A multiphase lattice Boltzmann flux solver (MLBFS) is proposed in this paper for incompressible multiphase flows with low- and large-density-ratios. In the solver, the flow variables at cell centers are given from the solution of macroscopic governing differential equations (Navier-Stokes equations recovered by multiphase lattice Boltzmann (LB) model) by the finite volume method. At each cell interface, the viscous and inviscid fluxes are evaluated simultaneously by local reconstruction of solution for the standard lattice Boltzmann equation (LBE). The forcing terms in the governing equations are directly treated by the finite volume discretization. The phase interfaces are captured by solving the phase-field Cahn-Hilliard equation with a fifth order upwind scheme. Unlike the conventional multiphase LB models, which restrict their applications on uniform grids with fixed time step, the MLBFS has the capability and advantage to simulate multiphase flows on non-uniform grids. The proposed solver is validated by several benchmark problems, such as two-phase co-current flow, Taylor-Couette flow in an annulus, Rayleigh-Taylor instability, and droplet splashing on a thin film at density ratio of 1000 with Reynolds numbers ranging from 20 to 1000. Numerical results show the reliability of the proposed solver for multiphase flows with high density ratio and high Reynolds number.
New Finite Difference Methods Based on IIM for Inextensible Interfaces in Incompressible Flows
Li, Zhilin; Lai, Ming-Chih
In this paper, new finite difference methods based on the augmented immersed interface method (IIM) are proposed for simulating an inextensible moving interface in an incompressible two-dimensional flow. The mathematical models arise from studying the deformation of red blood cells in mathematical biology. The governing equations are incompressible Stokes or Navier-Stokes equations with an unknown surface tension, which should be determined in such a way that the surface divergence of the velocity is zero along the interface. Thus, the area enclosed by the interface and the total length of the interface should be conserved during the evolution process. Because of the nonlinear and coupling nature of the problem, direct discretization by applying the immersed boundary or immersed interface method yields complex nonlinear systems to be solved. In our new methods, we treat the unknown surface tension as an augmented variable so that the augmented IIM can be applied. Since finding the unknown surface tension is essentially an inverse problem that is sensitive to perturbations, our regularization strategy is to introduce a controlled tangential force along the interface, which leads to a least squares problem. For Stokes equations, the forward solver at one time level involves solving three Poisson equations with an interface. For Navier-Stokes equations, we propose a modified projection method that can enforce the pressure jump condition corresponding directly to the unknown surface tension. Several numerical experiments show good agreement with other results in the literature and reveal some interesting phenomena. PMID:23795308
Computational design of natural laminar flow wings for transonic transport application
NASA Technical Reports Server (NTRS)
Waggoner, Edgar G.; Campbell, Richard L.; Phillips, Pamela S.; Viken, Jeffrey K.
Two research programs are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wind planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first program supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. Boundary-layer and static-pressure data will be measured on this design during the supporting wind-tunnel and flight tests. These data will then be analyzed and used to infer the relationship between crossflow and Tollmein-Schlichting disturbances on laminar boundary-layer transition. A wing was designed computationally for a corporate transport aircraft in the second program. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs. Wing surface pressure distributions, which support the design objective and were derived from transonic three-dimensional analyses codes, are also presented. Current status of each of the research programs is included in the summary.
Calculation of laminar flows with second-order schemes and collocated variable arrangement
NASA Astrophysics Data System (ADS)
Biagioli, Fernando
A numerical study of laminar flows is carried out to examine the performance of two second-order discretization schemes: a total variation diminishing scheme and a second-order upwind scheme. The former has the same form as the standard first-order hybrid central upwind scheme, but with a numerical diffusion reduced by the Van Leer limiter; the latter is based on the linear extrapolation of cell face values using the two upwind neighbors. A collocated grid arrangement is used; oscillations which could be generated by pressure-velocity decoupling are avoided via the Rhie-Chow interpolation. Two iterative solution methods are used: (i) the deferred correction procedure proposed by Khosla and Rubin and (ii) implicit treatment of the second-order upwind contribution. Three two-dimensional laminar test cases are considered for assessment: the plane lid-driven cavity, the plane backward facing step and the axisymmetric pipe with sudden contraction. Experimental data are available for the two last cases. Both the total variation diminishing and the second-order upwind schemes give wiggle-free results and can predict the flowfields more accurately than the standard first-order hybrid central upwind scheme.
Response of a laminar premixed flame to flow oscillations: A kinematic model and thermoacoustic instability results
Fleifil, M.; Annaswamy, A.M.; Ghoneim, A.F. [Massachusetts Inst. of Technology, Cambridge, MA (United States)] [Massachusetts Inst. of Technology, Cambridge, MA (United States); Ghoneim, Z.A. [Ain Shams Univ., Abassia (Egypt)] [Ain Shams Univ., Abassia (Egypt)
Combustion instability is a resonance phenomenon that arises due to the coupling between the system acoustics and the unsteady heat release. The constructive feedback between the two processes, which is known to occur as a certain phase relationship between the pressure and the unsteady heat release rate is satisfied, depends on many parameters among which is the acoustic mode, the flame holder characteristics, and the dominant burning pattern. In this paper, the authors construct an analytical model to describe the dynamic response of a laminar premixed flame stabilized on the rim of a tube to velocity oscillation. They consider uniform and nonuniform velocity perturbations superimposed on a pipe flow velocity profile. The model results show that the magnitude of heat release perturbation and its phase with respect to the dynamic perturbation dependent primarily on the flame Strohal number, representing the ratio of the dominant frequency times the tube radius to the laminar burning velocity. In terms of this number, high-frequency perturbations pass through the flame while low frequencies lead to a strong response. The phase with respect to the velocity perturbation behaves in the opposite way. Results of this model are shown to agree with experimental observations and to be useful in determining how the combustion excited model is selected among all the acoustic unstable modes. The model is then used to obtain a time-domain differential equation describing the relationship between the velocity perturbation and the heat release response over the entire frequency range.
Thermography investigations and numerical analysis of turbulent and laminar flow at light weight structures
NASA Astrophysics Data System (ADS)
Arndt, Ralf; Gaulke, Alexander
Thermography (IR) allows global visualization of temperature distribution on surfaces with high accuracy. This potential can be used for visualization of fluid mechanics effects at the intersection of laminar and turbulent flows, where temperature jumps appear due to convection and friction i.e. for the optimization in the design of airplane geometries. In civil engineering too it is the aspiration of the modern engineer of light weight structures to meet singular loads like wind peaks rather by intelligent structures and materials than by massive structures. Therefore the "Institute of Conceptual and Structural Design" of the Technical University of Berlin (TUB) is working on the development of adaptive structures, optimized geometry and intelligent microstructures on surfaces of structural elements. The paper shows the potential of modern computational fluid dynamics (CFD) in combination with thermography (IR) to optimize structures by visualization of laminar-tumultuous border layer currents. Therefore CFD simulations and IR wind tunnel experiments will be presented and discussed. For simulations and experiments - artificial and structural elements of the cable-stayed Strelasund Bridge, Germany, are used.
Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method
NASA Technical Reports Server (NTRS)
Loulou, Patrick; Moser, Robert D.; Mansour, Nagi N.; Cantwell, Brian J.
A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field.
Convective heat transfer in foams under laminar flow in pipes and tube bundles
Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent
The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux. PMID:25552745
On the nonlinear stability of the unsteady, viscous flow of an incompressible fluid in a curved pipe
Trudi A. Shortis; Philip Hall
The stability of the flow of an incompressible, viscous fluid through a pipe of circular cross-section curved about a central axis is investigated in a weakly nonlinear regime. A sinusoidal pressure gradient with zero mean is imposed, acting along the pipe. A WKBJ perturbation solution is constructed, taking into account the need for an inner solution in the vicinity of
On the nonlinear stability of the oscillatory viscous flow of an incompressible fluid in a curved pipe
Trudi A. Shortis; Philip Hall
The stability of the flow of an incompressible, viscous fluid through a pipe of circular cross-section, curved about a central axis is investigated in a weakly nonlinear regime. A sinusoidal pressure gradient with zero mean is imposed, acting along the pipe. A WKBJ perturbation solution is constructed, taking into account the need for an inner solution in the vicinity of
Three-dimensional Lagrangian transport phenomena in unsteady laminar flows driven by a rotating sphere
NASA Astrophysics Data System (ADS)
Moharana, N. R.; Speetjens, M. F. M.; Trieling, R. R.; Clercx, H. J. H.
Magnetic actuation of microscopic beads is a promising technique for enhancement and manipulation of scalar transport in micro-fluidic systems. This implies laminar and essentially three-dimensional (3D) unsteady flow conditions. The present study addresses fundamental transport phenomena in such configurations in terms of 3D coherent structures formed by the Lagrangian fluid trajectories in a 3D time-periodic flow driven by a rotating sphere. The flow field is represented by an exact Stokes solution superimposed by a nonlinear closed-form perturbation. This facilitates systematic "activation" and exploration of two fundamental states: (i) invariant spheroidal surfaces accommodating essentially 2D Hamiltonian dynamics; (ii) formation of intricate 3D coherent structures (spheroidal shells interconnected by tubes) and onset to 3D dynamics upon weak perturbation of the former state. Key to the latter state is emergence of isolated periodic points and the particular foliation and interaction of the associated manifolds, which relates intimately to coherent structures of the unperturbed state. The occurrence of such fundamental states and corresponding dynamics is (qualitative) similar to findings on a realistic 3D lid-driven flow subject to weak fluid inertia. This implies, first, a universal response scenario to weak perturbations and, second, an adequate representation of physical effects by the in essence artificial perturbation. The study thus offers important new insights into a class of flow configurations with great practical potential.
An efficient implicit direct forcing immersed boundary method for incompressible flows
NASA Astrophysics Data System (ADS)
Cai, S.-G.; Ouahsine, A.; Smaoui, H.; Favier, J.; Hoarau, Y.
A novel efficient implicit direct forcing immersed boundary method for incompressible flows with complex boundaries is presented. In the previous work [1], the calculation is performed on the Cartesian grid regardless of the immersed object, with a fictitious force evaluated on the Lagrangian points to mimic the presence of the physical boundaries. However the explicit direct forcing method [1] fails to accurately impose the non-slip boundary condition on the immersed interface. In the present work, the calculation is based on the implicit treatment of the artificial force while in an effective way of system iteration. The accuracy is also improved by solving the Navier-Stokes equation with the rotational incremental pressure- correction projection method of Guermond and Shen [2]. Numerical simulations performed with the proposed method are in good agreement with those in the literature.
Stabilized finite element schemes with LBB-stable elements for incompressible flows
NASA Astrophysics Data System (ADS)
Gelhard, Tobias; Lube, Gert; Olshanskii, Maxim A.; Starcke, Jan-Hendrik
We study stabilized FE approximations of SUPG type to the incompressible Navier-Stokes problem. Revisiting the analysis for the linearized model, we show that for conforming LBB-stable elements the design of the stabilization parameters for many practical flows differs from that commonly suggested in literature and initially designed for the case of equal-order approximation. Then we analyze a reduced SUPG scheme often used in practice for LBB-stable elements. To provide the reduced scheme with appropriate stability estimates we introduce a modified LBB condition which is proved for a family of FE approximations. The analysis is given for the linearized equations. Numerical experiments for some linear and nonlinear benchmark problems support the theoretical results.
An adaptive levelset method for computing solutions to incompressible two-phase flows.
NASA Astrophysics Data System (ADS)
Sussman, Mark; Lbnl Collaboration; Fatemi, Emad; Smereka, Peter; Osher, Stan
We present an adaptive level set method for computing 2d axisymmetric and fully 3d incompressible two-phase flow. Our methodology is specifically targeted at problems characterized by large density and viscosity jumps (e.g. air/water) and stiff, singular source terms, such as those due to surface tension. One such application is the modeling of ink-jet printers in which one wants to accurately model the break-up of the jet into droplets. We compare our method to the Volume-of-Fluid method and the Boundary Integral Method; we focus our comparison to problems in which a change in topology occurs. We also validate our method against experiments and theory.
Shear banding analysis of plastic models formulated for incompressible viscous flows
NASA Astrophysics Data System (ADS)
Lemiale, V.; M³hlhaus, H.-B.; Moresi, L.; Stafford, J.
We investigate shear band orientations for a simple plastic formulation in the context of incompressible viscous flow. This type of material modelling has been introduced in literature to enable the numerical simulation of the deformation and failure of the lithosphere coupled with the mantle convection. In the present article, we develop a linear stability analysis to determine the admissible shear band orientations at the onset of bifurcation. We find that the so-called Roscoe angle and Coulomb angle are both admissible solutions. We present numerical simulations under plane strain conditions using the hybrid particle-in-cell finite element code Underworld. The results both in compressional and extensional stress conditions show that the variation of the numerical shear bands angle with respect to the internal friction angle follows closely the evolution of the Coulomb angle.
HYBRID LAMINAR FLOW TECHNOLOGY Partner: EADS Airbus (D) (Coordinator), Apparatebau Gauting (D), EADS Airbus (F), Aerospace Systems and
Berlin,Technische Universitõt
high drag HLFC via suction causes laminar flow therefore lower drag HYLTEC topics: Consequences/LaTec and EC (HYLDA) funded flight tests with A320 No. 1, HLFC applied at vertical tail Technical feasibility proven No show stopper for HLFC was found Impact of suction on aircraft drag A320 HLF Flight Test HYLTEC
Numerical study of two dimensional laminar boundary layer compressible flow with pressure gradient and heat and mass transfer
N. Kafoussias; A. Karabis; M. Xenos
The aim of this work is the study of the two dimensional laminar compressible boundary layer flow, with an adverse pressure gradient in the presence of heat and mass transfer. The partial differential equations and their boundary conditions, describing the problem under consideration, are transformed using the compressible Falkner¢Skan transformation and the numerical solution of the problem is obtained by
An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour¢gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...
A Spalart-Allmaras turbulence model implementation in a discontinuous Galerkin solver for incompressible flows
NASA Astrophysics Data System (ADS)
Crivellini, Andrea; D'Alessandro, Valerio; Bassi, Francesco
In this paper the artificial compressibility flux Discontinuous Galerkin (DG) method for the solution of the incompressible Navier-Stokes equations has been extended to deal with the Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the Spalart-Allmaras (SA) turbulence model. DG implementations of the RANS and SA equations for compressible flows have already been reported in the literature, including the description of limiting or stabilization techniques adopted in order to prevent the turbulent viscosity ?ś from becoming negative. In this paper we introduce an SA model implementation that deals with negative ?ś values by modifying the source and diffusion terms in the SA model equation only when the working variable or one of the model closure functions become negative. This results in an efficient high-order implementation where either stabilization terms or even additional equations are avoided. We remark that the proposed implementation is not DG specific and it is well suited for any numerical discretization of the RANS-SA governing equations. The reliability, robustness and accuracy of the proposed implementation have been assessed by computing several high Reynolds number turbulent test cases: the flow over a flat plate (Re=107), the flow past a backward-facing step (Re=37400) and the flow around a NACA 0012 airfoil at different angles of attack (?=0░, 10░, 15░) and Reynolds numbers (Re=2.88ū106,6ū106).
Design considerations for application of laminar flow control systems to transport aircraft
NASA Technical Reports Server (NTRS)
Braslow, A. L.; Fischer, M. C.
The current status of the laminar-flow control LFC technology is summarized. Factors that have previously inhibited the application of LFC are first reviewed. Involved are the effects of atmospheric ice crystals, surface irregularities, acoustical environment, and off-design operating conditions. Aircraft design trends that are different from turbulent aircraft are discussed as are various design requirements unique to the LFC systems. Current design approaches for the principal LFC systems are reviewed. These include the system for protection of the leading-edge region from surface contamination and icing and the system for removal of a portion of the boundary-layer air. The latter includes consideration of both multiple spanwise suction slots and distributed perforations and required differences between the wing-box and leading-edge box regions.
Investigation of radiative interaction in laminar flows using Monte Carlo simulation
NASA Technical Reports Server (NTRS)
Liu, Jiwen; Tiwari, S. N.
The Monte Carlo method (MCM) is employed to study the radiative interactions in fully developed laminar flow between two parallel plates. Taking advantage of the characteristics of easy mathematical treatment of the MCM, a general numerical procedure is developed for nongray radiative interaction. The nongray model is based on the statistical narrow band model with an exponential-tailed inverse intensity distribution. To validate the Monte Carlo simulation for nongray radiation problems, the results of radiative dissipation from the MCM are compared with two available solutions for a given temperature profile between two plates. After this validation, the MCM is employed to solve the present physical problem and results for the bulk temperature are compared with available solutions. In general, good agreement is noted and reasons for some discrepancies in certain ranges of parameters are explained.
Designing a Hybrid Laminar-Flow Control Experiment: The CFD-Experiment Connection
NASA Technical Reports Server (NTRS)
Streett, C. L.
The NASA/Boeing hybrid laminar flow control (HLFC) experiment, designed during 1993-1994 and conducted in the NASA LaRC 8-foot Transonic Pressure Tunnel in 1995, utilized computational fluid dynamics and numerical simulation of complex fluid mechanics to an unprecedented extent for the design of the test article and measurement equipment. CFD was used in: the design of the test wing, which was carried from definition of desired disturbance growth characteristics, through to the final airfoil shape that would produce those growth characteristics; the design of the suction-surface perforation pattern that produced enhanced crossflow-disturbance growth: and in the design of the hot-wire traverse system that produced minimal influence on measured disturbance growth. These and other aspects of the design of the test are discussed, after the historical and technical context of the experiment is described.
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
Results of a 2-year study are reported which were carried out to extend the development of laminar flow control (LFC) technology and evaluate LFC systems concepts. The overall objective of the LFC program is to provide a sound basis for industry decisions on the application of LFC to future commercial transports. The study was organized into major tasks to support the stated objectives through application of LFC systems concepts to a baseline LFC transport initially generated for the study. Based on competitive evaluation of these concepts, a final selection was made for incorporation into the final design of an LFC transport which also included other advanced technology elements appropriate to the 1990 time period.
Evaluation of Laminar Flow Control System Concepts for Subsonic Commercial Transport Aircraft
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
Alternatives in the design of laminar flow control (LFC) subsonic commerical transport aircraft for opeation in the 1980's period were studied. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12, 038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatices in the areas of aerodynamics, structures and materials, LFC systems, leading-edge region cleaning, and integration of auxiliary systems were studied. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in DOC but provides descreases of 8.2% in gross weight and 21.7% in fuel consumption.
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
A two-year study conducted to establish a basis for industry decisions on the application of laminar flow control (LFC) to future commercial transports was presented. Areas of investigation included: (1) mission definition and baseline selection; (2) concepts evaluations; and (3) LFC transport configuration selection and component design. The development and evaluation of competing design concepts was conducted in the areas of aerodynamics, structures and materials, and systems. The results of supporting wind tunnel and laboratory testing on a full-scale LFC wing panel, suction surface opening concepts and structural samples were included. A final LFC transport was configured in incorporating the results of concept evaluation studies and potential performance improvements were assessed. Remaining problems together with recommendations for future research are discussed.
Quasi-three-dimensional laminar boundary-layer separations in supersonic flow
NASA Technical Reports Server (NTRS)
Vatsa, V. N.; Werle, M. J.
A numerical algorithm is presented for solving laminar, steady, supersonic interacting boundary-layer flows for quasi-three-dimensional configurations. The interaction problem is treated as a boundary-value problem and a salient feature of the scheme is the direct implementation of the downstream boundary condition. Solutions are presented for axisymmetric and swept (yawed) compression ramps for both adiabatic and heat transfer conditions over a Mach number range of 2-6. The results are in good agreement with experimental data and existing theories for axisymmetric cases. For the swept (yawed) configurations, lack of experimental data makes a direct comparison impossible, but the present solutions are found to be in qualitative agreement with earlier studies. In addition it is shown that the trends obtained here for the sweep effects are well predicted by a simple extension of the two-dimensional asymptotic theory.
On the importance of the pressure dependence of viscosity in steady non-isothermal shearing flows of compressible and incompressible fluids and in the isothermal fountain flow
R. R. Huilgol; Z. You
Four steady non-isothermal viscometric flows of a class of compressible and incompressible fluids with a viscosity depending on the shear rate, pressure and temperature are considered and consistency relations between the pressure gradient in the flow direction and that in the direction of the velocity gradient are derived. In particular, the dependence of the viscosity on the pressure plays the
Fatigue response of perforated titanium for application in laminar flow control
NASA Technical Reports Server (NTRS)
Johnson, W. Steven; Miller, Jennifer L.; Newman, Jr., James
The room temperature tensile and fatigue response of non-perforated and perforated titanium for laminar flow control application was investigated both experimentally and analytically. Results showed that multiple perforations did not affect the tensile response, but did reduce the fatigue life. A two dimensional finite element stress analysis was used to determine that the stress fields from adjacent perforations did not influence one another. The stress fields around the holes did not overlap one another, allowing the materials to be modeled as a plate with a center hole. Fatigue life was predicted using an equivalent MW flow size approach to relate the experimental results to microstructural features of the titanium. Predictions using flaw sizes ranging from 1 to 15 microns correlated within a factor of 2 with the experimental results by using a flow stress of 260 MPa. By using two different flow stresses in the crack closure model and correcting for plasticity, the experimental results were bounded by the predictions for high applied stresses. Further analysis of the complex geometry of the perforations and the local material chemistry is needed to further understand the fatigue behavior of the perforated titanium.
Numerical simulation of laminar plasma dynamos in a cylindrical von Karman flow
Khalzov, I. V.; Brown, B. P.; Schnack, D. D.; Forest, C. B. [University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706 (United States); Ebrahimi, F. [University of New Hampshire, 8 College Road, Durham, New Hampshire 03824 (United States)
The results of a numerical study of the magnetic dynamo effect in cylindrical von Karman plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model. We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von Karman flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field saturates at an amplitude corresponding to a new stable equilibrium (a laminar dynamo). We show that compressibility in the plasma results in an increase of the critical magnetic Reynolds number, while inclusion of the Hall term in Ohm's law changes the amplitude of the saturated dynamo field but not the critical value for the onset of dynamo action.
Influence of vibration amplitude on laminar flow over a plate vibrating at low Strouhal number
Venkat, N.K. (Spaulding Environmental Associates, Inc., Wakefield, RI (United States)); Spaulding, M. (Univ. of Rhode Island, Kingston, RI (United States). Dept. of Ocean Engineering)
The spectral and hydrodynamic response of laminar flow over a flat plate with a vibrating section forced in sinusoidal motion with a dimensionless amplitude ratio, H[sub 0] (vibration amplitude divided by plate length) varying in the range 0.0 < H[sub 0] < 0.1 is analyzed using numerical simulations. The Reynolds number, Re, based on the length of the vibrating plate, is fixed at 1,000. The flow is simulated for Strouhal number, St, = 0.25 (low frequency). The spectral characteristics are obtained by performing Fast Fourier Transform (FFT) on the pressure coefficient time series data. The hydrodynamic analysis is performed by plotting stream function contour plot in the vicinity of the vibrating section for one vibration cycle. The model predicted results show that the friction and pressure coefficients over the vibrating body vary with vibration amplitude. For low amplitude ratios, the interaction of the external flow with the vibrating section is linear and there is little up or downstream influence. For high H[sub 0], there is considerable downstream influence of the disturbance. Nonlinear energy transfer, as evidenced by the existence of a significant first harmonic in the pressure wave, takes place between the vibrating plate and the flow field. Energy transfer to the higher harmonics is less significant.
Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes
NASA Astrophysics Data System (ADS)
Sasmito, Agus Pulung; Kurnia, Jundika Candra; Mujumdar, Arun Sadashiv
Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance.
Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes.
Sasmito, Agus Pulung; Kurnia, Jundika Candra; Mujumdar, Arun Sadashiv
Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance. PMID:21711901
Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes
Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance. PMID:21711901
The Fictitious Boundary Method for the Implicit Treatment of Dirichlet Boundary Conditions with Applications to Incompressible Flow Simulations
Stefan Turek; Decheng Wan; Liudmila S. Rivkind
\\u000a A æfictitious boundary methodÆ for computing incompressible flows with complicated small-scale and\\/or time-dependent geometric\\u000a details is presented. The underlying technique is based on a special treatment of Dirichlet boundary conditions, particularly\\u000a for FEM discretizations, together with so-called `iterative filtering techniquesÆ in the context of hierarchical multigrid\\u000a approaches such that the flow can be efficienctly computed on a fixed computational mesh
A stabilized MLPG method for steady state incompressible fluid flow simulation
NASA Astrophysics Data System (ADS)
Wu, Xue-Hong; Tao, Wen-Quan; Shen, Sheng-Ping; Zhu, Xing-Wang
In this paper, the meshless local Petrov-Galerkin (MLPG) method is extended to solve the incompressible fluid flow problems. The streamline upwind Petrov-Galerkin (SUPG) method is applied to overcome oscillations in convection-dominated problems, and the pressure-stabilizing Petrov-Galerkin (PSPG) method is applied to satisfy the so-called Babu\\vska-Brezzi condition. The same stabilization parameter ?( ?SUPG = ?PSPG) is used in the present method. The circle domain of support, linear basis, and fourth-order spline weight function are applied to compute the shape function, and Bubnov-Galerkin method is applied to discretize the PDEs. The lid-driven cavity flow, backward facing step flow and natural convection in the square cavity are applied to validate the accuracy and feasibility of the present method. The results show that the stability of the present method is very good and convergent solutions can be obtained at high Reynolds number. The results of the present method are in good agreement with the classical results. It also seems that the present method (which is a truly meshless) is very promising in dealing with the convection- dominated problems.
A unified approach for numerical simulation of viscous compressible and incompressible flows over adiabatic and isothermal walls
NASA Technical Reports Server (NTRS)
Hafez, M.; Soliman, M.; White, S.
A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.
Steady and unsteady laminar flows of Newtonian and generalized Newtonian fluids in a planar T-junction
A. I. P. Miranda; P. J. Oliveira; F. T. Pinho
SUMMARY An investigation of laminar steady and unsteady flows in a two-dimensional T-junction was carried out for Newtonian and a non-Newtonian fluid analogue to blood. The flow conditions considered are of relevance to hemodynamical applications and the localization of coronary diseases, and the main objective was to quantify the accuracy of the predictions and to provide benchmark data that are
Incompressible fluid binary systems with internal flows -- models of close binary neutron star systems with spin
Koji Uryu; Yoshiharu Eriguchi
In this paper we have examined numerically exact configurations of close binary systems composed of incompressible fluids with internal flows. Component stars of binary systems are assumed to be circularly orbiting each other but rotating nonsynchronously with the orbital motion, i.e. stars in binary systems have steady motions seen from a rotational frame of reference. We have computed several equilibrium sequences by taking fully into account the tidal effect of Newtonian gravity without approximation. We consider two binary systems consisting of either 1) a point mass and a fluid star or 2) a fluid star and a fluid star. Each of them corresponds to generalization of the Roche--Riemann or the Darwin--Riemann problem, respectively. Our code can be applied to various types of incompressible binary systems with various mass ratios and spin as long as the vorticity is constant. We compare these equilibrium sequences of binaries with approximate solutions which were studied extensively by Lai, Rasio and Shapiro (LRS) as models for neutron star--neutron star (NS--NS) binary systems or black hole--neutron star (BH--NS) binary systems. Our results coincide qualitatively with those of LRS but are different from theirs for configurations with small separations. For these binary systems, our sequences show that dynamical or secular instability sets in as the separation decreases. The quantitative errors of the ellipsoidal approximation amount to 2\\sim 10% for configurations near the instability point. Compared to the results of LRS, the separation of the stars at the point where the instability sets in is larger and correspondingly the orbital frequency at the critical state is smaller for our models.
Nusselt number correlations for simultaneously developing laminar duct flows of liquids with temperature dependent properties
NASA Astrophysics Data System (ADS)
Del Giudice, Stefano; Savino, Stefano; Nonino, Carlo
New correlations, suitable for engineering applications, for the mean Nusselt number in the entrance region of circular tubes and square ducts with uniform heat flux boundary conditions specified at the walls are proposed. These correlations are obtained on the basis of the results of a previous parametric investigation on the effects of temperature dependent viscosity and thermal conductivity in simultaneously developing laminar flows of liquids in straight ducts of constant cross-sections. In these studies, a finite element procedure has been employed for the numerical solution of the parabolized momentum and energy equations. Viscosity and thermal conductivity are assumed to vary with temperature according to an exponential and to a linear relation, respectively, while the other fluid properties are held constant. Axial distributions of the mean Nusselt number, obtained by numerical integration from those of the local Nusselt number, are used as input data in the derivation of the proposed correlations. A superposition method is proved to be applicable in order to estimate the Nusselt number by considering separately the effects of temperature dependent viscosity and thermal conductivity. Therefore, for each of the considered cross-sectional geometries, two distinct correlations are proposed for flows of liquids with temperature dependent viscosity and with temperature dependent thermal conductivity, in addition to that obtained for constant property flows.
A comparative study of sound generation by laminar, combusting and non-combusting jet flows
NASA Astrophysics Data System (ADS)
Talei, Mohsen; Brear, Michael J.; Hawkes, Evatt R.
Sound production by two-dimensional, laminar jet flows with and without combustion is studied numerically and theoretically. The compressible Navier-Stokes, energy and progress variable equations are solved by resolving both the near field and the acoustics. The combusting jet flows are compared to non-combusting jets of the same jet Mach number, with the non-combusting, non-isothermal jets having the same steady temperature difference as the combusting jets. This infers that the magnitude of entropic and density disturbances is similar in some of the combusting and non-combusting cases. The flows are perturbed by a sinusoidal inlet velocity fluctuation at different Strouhal numbers. The computational domain is resolved to the far field in all cases, allowing direct examination of the sound radiated and its sources. Lighthill's acoustic analogy is then solved numerically using Green's functions. The radiated sound calculated using Lighthill's equation is in good agreement with that from the simulations for all cases, validating the numerical solution of Lighthill's equation. The contribution of the source terms in Dowling's reformulation of Lighthill's equation is then investigated. It is shown that the source term relating to changes in the momentum of density inhomogeneities is the dominant source term for all non-reacting, non-isothermal cases. Further, this source term has similar magnitude in the combusting cases and is one of the several source terms that have similar magnitude to the source term involving fluctuations in the heat release rate.
Immunoassay on a power-free microchip with laminar flow-assisted dendritic amplification.
Hosokawa, Kazuo; Omata, Masaki; Maeda, Mizuo
We demonstrate a rapid (<30 min) and ultrasensitive (sub-picomolar) immunoassay on a microchip which needs no external power sources for fluid transport. We previously reported a rapid immunoassay of human C-reactive protein (CRP) on the power-free microchip with moderate sensitivity, i.e., a limit of detection (LOD) in sub-nanomolar range, due to the lack of signal amplification. In the current work, we have improved the LOD by 3 orders of magnitude by employing dendritic amplification (DA) methods. Specifically, a sandwich immunocomplex with a biotinylated secondary antibody was constructed on the inner surface of the microchannel as described in the previous report. Onto the immunocomplex, solutions of FITC-labeled streptavidin (F-SA) and biotinylated anti-streptavidin (B-anti-SA) were supplied to grow a dendritic structure. First, we alternately supplied the two solutions for layer-by-layer growth up to three layers. As a result, we obtained an LOD of 0.21 pM with a CRP sample volume of 1.0 microL and assay time of approximately 30 min under an ordinary fluorescence microscope. Second, to reduce the number of incubation steps, we have devised a new DA method: laminar flow-assisted dendritic amplification (LFDA). In this method, F-SA and B-anti-SA were simultaneously and continuously supplied from two laminar streams formed by a Y-shaped microchannel. The immunoassay with the LFDA for 10 min (total assay time of approximately 23 min) with a CRP sample volume of 0.5 microL yielded an LOD of 0.15 pM, which is equivalent to 75 zmol. The combination of the power-free microchip and the LFDA will provide a new opportunity for ultrasensitive point-of-care testing. PMID:17614367
A consistent projection-based SUPG/PSPG XFEM for incompressible two-phase flows
NASA Astrophysics Data System (ADS)
Liao, Jian-Hui; Zhuang, Zhuo
In this paper, a consistent projection-based streamline upwind/pressure stabilizing Petrov-Galerkin (SUPG/PSPG) extended finite element method (XFEM) is presented to model incompressible immiscible two-phase flows. As the application of linear elements in SUPG/PSPG schemes gives rise to inconsistency in stabilization terms due to the inability to regenerate the diffusive term from viscous stresses, the numerical accuracy would deteriorate dramatically. To address this issue, projections of convection and pressure gradient terms are constructed and incorporated into the stabilization formulation in our method. This would substantially recover the consistency and free the practitioner from burdensome computations of most items in the residual. Moreover, the XFEM is employed to consider in a convenient way the fluid properties that have interfacial jumps leading to discontinuities in the velocity and pressure fields as well as the projections. A number of numerical examples are analyzed to demonstrate the complete recovery of consistency, the reproduction of interfacial discontinuities and the ability of the proposed projection-based SUPG/PSPG XFEM to model two-phase flows with open and closed interfaces.
Multi-field finite element methods with discontinuous pressures for axisymmetric incompressible flow
NASA Astrophysics Data System (ADS)
Ruas, V.; Carneiro de Araujo, J. H.; Silva Ramos, M. A. M.
Two- and three-field methods are studied for solving the Stokes system in the axisymmetric case, as a linearized form of different types of fluid flow equations. Both are designed for the standard Galerkin formulation expressed in terms either of the velocity and the pressure, or of these two fields together with the extra-stress tensor, and use discontinuous pressure spaces. The first method is related to the rectangular based Q2-P1 element due to Fortin. The other one is linked to the Crouzeix-Raviart triangle. Both methods satisfy the uniform stability (inf-sup) condition relating the velocity and pressure representations, expressed in terms of the natural weighed Sobolev norms, for the system under consideration. This condition is fundamental to derive second-order convergence results for solution methods of viscous or viscoelastic incompressible flow problems based on the corresponding finite element spaces. In order to illustrate this, some numerical results using a method of this type studied by the authors are presented, in connection with the three-field formulation of the Stokes system related to viscoelastic fluids.
An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows
Snider, D.M. [SAIC, Albuquerque, NM (United States); O`Rourke, P.J. [Los Alamos National Lab., NM (United States); Andrews, M.J. [Texas A and M Univ., College Station, TX (United States). Dept. of Mechanical Engineering
A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.
Structural development of laminar flow control aircraft chordwise wing joint designs
NASA Technical Reports Server (NTRS)
Fischler, J. E.; Jerstad, N. M.; Gallimore, F. H., Jr.; Pollard, T. J.
For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for unavoidable eccentricity, which was reduced and reacted satisfactorily by the rib supports. It should also result in a relatively simple low-cost installation, and makes it easy to replace any panels damaged in the field.
Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow
This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60░C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration. PMID:21827644