Effect of grid sensitivity on the performance of wall adapting SGS models for LES of swirling and separating reattaching flows

TL;DR

This study evaluates how grid resolution affects the performance of wall-adapting SGS models in LES of swirling and separating flows, finding the Dynamic WALE model is most consistent across different grid sensitivities.

Contribution

It compares the grid sensitivity of three SGS models in LES of complex flows, highlighting the robustness of the Dynamic WALE model across different grid resolutions.

Findings

Dynamic WALE model is almost insensitive to grid resolution changes.

Fine grid (y+ = 20) improves near-wall eddy viscosity predictions.

Dynamic WALE model predictions are closest to experimental data.

Abstract

The present study assesses the performance of the Wall Adapting SGS models along with the Dynamic Smagorinsky model for flows involving separation, reattachment and swirl. Due to the simple geometry and wide application in a variety of engineering systems, the Backward-Facing Step (BFS) geometry and Confined Swirling Flow (CSF) geometry are invoked in the present case. The calculation of the SGS stresses employs three models, namely, the Dynamic Smagorinsky model, the Wall Adapting Local Eddy viscosity (WALE) model and the Dynamic WALE model. For studying the effect of the grid sensitivity, the simulations are performed over two sets of grids with different resolutions based on the non-dimensional wall distance parameter ( y+ ). Grids corresponding to y+ = 70 and y+ = 20 are employed for the subsonic flow over the BFS while grids corresponding to y+ = 40 and y+ = 20 are employed for supersonic flow over the BFS and for confined swirling flow geometry. The validation against the experimental results includes the mean flow fields and the turbulent stresses obtained for each case. The results reveal that for the fine grid (y+ = 20), the near wall eddy viscosity profile for the WALE model is better than both the Dynamic WALE and the Dynamic Smagorinsky model. The difference between the predictions of the coarse and fine grids for Dynamic Smagorinsky and the WALE model is high whereas, the Dynamic WALE model is almost insensitive to the grid resolutions considered for the present case. The mean velocity and pressure values as well as the turbulent quantities predicted by the Dynamic WALE model are closest to the experimental values for all the cases.