Off-wall boundary conditions for large-eddy simulation based on near-wall turbulence prediction

Abstract

Wall-modeled large-eddy simulation (LES) is currently the only affordable technique toward the eddy-resolving simulation of high-Reynolds number wall turbulence. Treatment of near-wall region in LES has drawn much attention in recent studies of wall turbulence and computational fluid dynamics. Traditional wall models typically relate the wall stress to the velocity through prescribed algebraic relations or the thin boundary layer equation. In the present study, we developed a new method for the treatment of near-wall region in LES based on the off-wall boundary conditions. The method combines the minimum flow units [Yin et al., “Prediction of near-wall turbulence using minimal flow unit,” J. Fluid Mech. 841, 654–673 (2018)] and the predictive inner–outer (PIO) model for wall turbulence [Marusic et al., “Predictive model for wall-bounded turbulent flow,” Science 329, 193–196 (2010)]. Fluctuating near-wall velocity field is predicted in real time to supply boundary conditions on the off-wall boundary. This method does not assume any velocity profile of the flow, but rather exploits the well-established universality of near-wall turbulence, and incorporates turbulent structures in the boundary conditions. We derived the expressions of the velocity and the subgrid-scale (SGS) stress boundary conditions in combination with the PIO model, and proved that the modulation effect and the fluctuating part of the SGS stress are not necessary for the off-wall boundary conditions. Through comparisons with other wall models, the current method is found to induce a shorter transition zone in the wall-normal direction. The validity and robustness of the method are verified by the reasonable simulation results of channel flows under different computational parameters.