Anisotropic Subgrid-Scale Stress Improves Wall-Modeled Large-Eddy Simulation of Turbulent Flow Separation
Researchers found that incorporating anisotropic subgrid-scale (SGS) stress into wall-modeled large-eddy simulations (WMLES) produces more consistent predictions of turbulent flow separation over a Gaussian-shaped bump than standard eddy-viscosity-based models. The study identifies the windward side of the bump, where a strong favorable pressure gradient exists, as the critical region where SGS anisotropy most influences downstream flow separation. These findings suggest that commonly used eddy-viscosity SGS models may be fundamentally insufficient for accurately simulating wall-bounded turbulent flows with pressure-gradient-driven separation.
A study posted to arXiv examines how anisotropic subgrid-scale (SGS) stress affects wall-modeled large-eddy simulation (WMLES) of turbulent flow over a spanwise-uniform Gaussian bump, focusing on the prediction of smooth-body flow separation. Standard eddy-viscosity-based SGS models were found to produce non-monotonic predictions of mean separation bubble size on the leeward side of the bump as the computational grid is refined, a sign of inconsistent numerical behavior. In contrast, models that incorporate anisotropic SGS stress yield more grid-consistent results. By selectively introducing anisotropic SGS stress in different regions of the domain, the authors pinpoint the windward side — where a strong favorable pressure gradient (FPG) acts — as the location most critical to accurate downstream separation prediction. Analysis of the Reynolds stress transport equation reveals that fluctuations in anisotropic SGS stress alter SGS dissipation and diffusion in the FPG region, which in turn modifies Reynolds stresses and the onset of separation. The improvement is attributed primarily to the inclusion of normal stress components in the SGS tensor, and an a priori study using filtered direct numerical simulation of turbulent Couette-Poiseuille flow under FPG conditions corroborates that anisotropic models provide a more physically realistic SGS stress representation.
What's missing
The study is a preprint and has not yet undergone formal peer review. The findings are demonstrated for a specific canonical geometry (a Gaussian bump) and a single auxiliary flow (Couette-Poiseuille); generalizability to more complex three-dimensional geometries or higher Reynolds-number industrial flows remains untested. Computational cost comparisons between anisotropic and eddy-viscosity-based SGS models are not discussed, which is a practical consideration for adoption in engineering applications.
What different sources said
- arXiv physicsCenter
Effect of subgrid-scale anisotropy on wall-modeled large-eddy simulation of turbulent flow with smooth-body separation
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