Title: A Coherent vorticity preserving eddy viscosity correction for Large-Eddy Simulation,
Abstract: This paper introduces a new approach to Large-Eddy Simulation (LES) where
subgrid-scale (SGS) dissipation is applied proportionally to the degree of
local spectral broadening, hence mitigated or deactivated in regions dominated
by large-scale and/or laminar vortical motion. The proposed Coherent vorticity
preserving (CvP) LES methodology is based on the evaluation of the ratio of the
test-filtered to resolved (or grid-filtered) enstrophy $\sigma$. Values of
$\sigma$ close to 1 indicate low sub-test-filter turbulent activity, justifying
local deactivation of the SGS dissipation. The intensity of the SGS dissipation
is progressively increased for $\sigma < 1$ which corresponds to a small-scale
spectral broadening. The SGS dissipation is then fully activated in developed
turbulence characterized by $\sigma \le \sigma_{eq}$, where the value
$\sigma_{eq}$ is derived assuming a Kolmogorov spectrum. The proposed approach
can be applied to any eddy-viscosity model, is algorithmically simple and
computationally inexpensive. LES of Taylor-Green vortex breakdown demonstrates
that the CvP methodology improves the performance of traditional, non-dynamic
dissipative SGS models, capturing the peak of total turbulent kinetic energy
dissipation during transition. Similar accuracy is obtained by adopting
Germano's dynamic procedure albeit at more than twice the computational
overhead. A CvP-LES of a pair of unstable periodic helical vortices is shown to
predict accurately the experimentally observed growth rate using coarse
resolutions. The ability of the CvP methodology to dynamically sort the
coherent, large-scale motion from the smaller, broadband scales during
transition is demonstrated via flow visualizations. LES of compressible channel
are carried out and show a good match with a reference DNS.