Large Eddy Simulation of Rearward-Facing Step Flow

Abstract

In conventional large eddy simulation (LES) models, the filtered Navier-Stokes equations (NSE) are supplemented by subgrid-scale (SGS) models that emulate the energy transfer from large scales toward the subgrid scales, where it will eventually be dissipated by molecular viscosity. An alternative approach involves solving the unfiltered NSE using high-resolution monotone algorithms for which implicit SGS models are provided by the intrinsic nonlinear high-frequency filters built into the convection discretization. This monotonically integrated LES (MILES) model is to be distinguished from underresolved direct numerical simulation models relying on other numerical methods (not necessarily monotonic) to represent the required damping, which will not necessarily ensure the correct distribution of energy among the large scales. Results from LES and MILES of turbulent rearward-facing step flows suggest that LES is independent of the details of the SGS model if it can adequately channel kinetic energy out of eddies close to the cutoff wave number to prevent aliasing, provided that the resolution is fine enough to ensure that the cutoff wave number is within the inertial subrange. Comparison with experimental data indicates good agreement for global quantities and first- and second-order statistical moments of velocity. Based on the simulations and the comparison with experimental data, the behavior of the flow in the free shear layer and in the reattachment region is presented together with a discussion of flow separation and reattachment.