A dynamic hybrid RANS/LES approach based on the local flow structure

By extracting the structural function from Vreman eddy-viscosity subgrid-scale model, a new turbulent length scale, which could quantify the degree of the instability of the local flow, is proposed. A hybrid RANS/LES method that combines both this kind of length scale and wall distance is obtained. The new model is capable of automatically determining the “transition” from RANS region to LES region according to the local flow state, instead of just taking the grid spacing into consideration. To investigate the WMLES (Wall-modeled LES) capability of this model, it is applied to fully-developed plane channel flows with two coarse grids whose grid numbers in wall parallel directions are respectively 37 × 37 and 49 × 49. Reτ ranges from 590 to 12,500. Most of the turbulent structures are resolved and sufficient resolved stresses are provided even near the wall. The prediction of mean velocity profiles is adequately accurate, and the phenomenon of “log layer mismatch” is removed. Flows pass a circular cylinder at subcritical Reynolds number is selected as an additional test case to explore the new model's performance subjected to separated flows. The present model has the potential of obtaining encouraging results with economical computation cost.