Comparison of upper boundary conditions for RANS used in wall-modeled large eddy simulation

Abstract

The hybrid RANS/LES using zonal approach with wall shear stress model is one of the wall-modeled large eddy simulation (WMLES) techniques developed to reduce computation cost in high Reynolds number flow simulations. In this approach, how to exchange flow field information between solutions from a wall model and LES through the boundary conditions is one of the important issues. In general, the wall boundary condition of LES is given as the instantaneous wall shear stress obtained in the wall model RANS, whereas the upper boundary condition for RANS is provided as the instantaneous velocity component acquired from the solution of LES. However, it does not guarantee an accurate estimation of wall shear stress due to a resolved portion of turbulent shear stresses in RANS. In this study, a new WMLES is suggested which is directly imposing the instantaneous total shear stress obtained in LES as the upper boundary condition for RANS, rather than velocity component and assessed in turbulent channel and boundary layer flows. It is shown that the present WMLES based on the total shear stress boundary condition predicted the logarithmic velocity profile and the low-order turbulence statistics at high Reynolds numbers even with very coarse grid resolution.