Alternative LES and Hybrid RANS/LES for Turbulent Flows

Abstract

After more than 30 years of intense research on large-eddy simulations (LES) of turbulent flows based on eddy-viscosity subfilter models, 1, there is now consensus that such an approach is subject to fundamental limitations. It has been demonstrated for a number of different flows that the shear stress and strain tensors involved in subfilter eddy-viscosity models have different topological features rendering scalar eddy-viscosity models inaccurate. There have been other proposals that do not employ the assumption of colinearity of strain and stress embedded in the eddy-viscosity models, e.g., the scale-similarity model of Bardina 2. However, such models are numerically unstable, and more recent efforts have focused on developing mixed models, combining in essence the dissipative eddy-viscosity models with the more accurate but unstable scale-similarity models. The results from such mixed models have been mostly satisfactory but the implementation and computational complexity of the combined approach have limited its popularity.