A Nested-LES Approach for Computation of High-Reynolds Number, Equilibrium and Non-Equilibrium Turbulent Wall-Bounded Flows.

Abstract

Computation of high Reynolds number, complex, non-equilibrium wall-bounded turbulent flows presents a major challenge for large-eddy simulation (LES), due to the stringent resolution requirements in the near-wall region in conventional LES, and the inability of existing wall models to accurately capture the near-wall dynamics in flows involving complex physics in the near-wall region. In this study, a novel nested-LES approach for computation of high Reynolds number, equilibrium and non-equilibrium, wall-bounded turbulent flows is proposed. The method couples well-resolved LES in a minimal flow unit with coarse-resolution LES in the full domain to provide high-fidelity simulations of the flow physics in both the inner and outer layers. The coupling between the two domains of nested-LES is achieved by dynamically renormalizing the velocity fields in each domain at each time-step during the course of the simulation to match the wall-normal profiles of the single-time ensemble-averaged kinetic energies of the components of mean and fluctuating velocities in both domains to those of the minimal flow unit in the inner layer, and to those of the full domain in the outer layer. The proposed nested-LES approach can be applied to any flows with at least one direction of local or global homogeneity, while reducing the required number of grid points from O(Re_t^2) of conventional LES to O(log{Re_t}) and O(Re_t^1) in flows with two or one directions of homogeneity, respectively.

The proposed nested-LES approach has been applied to LES of equilibrium turbulent channel flow at Re_t ~= 1000 - 10000, and non-equilibrium, strained turbulent channel flow at Re_t ~=2000. In application to equilibrium turbulent channel flow, the nested-LES approach predicts the skin-friction coefficient, first-order turbulence statistics, higher-order moments, two-point correlations, correlation maps, and structural features of the flow in agreement with available direct numerical simulation (DNS) and experimental data. In application to non-equilibrium, strained turbulent channel flow, nested-LES predicts the evolution of skin-friction coefficients and one-point turbulence statistics in good agreement with experimental data in shear-driven, three-dimensional turbulent boundary-layer (TBL).