Large eddy simulation of turbulent flow downstream of a backward-facing step

large eddy simulation is used to predict turbulent flow in the separated and reattached flow regions downstream of a backward-facing step.Simulations were carried out at a Reynolds number of 28 000 (based on the step height and the upstream centreline velocity) with a channel expansion ratio of 1.25. Two subgrid-scale models were tested, namely the dynamic eddy-viscosity, and the dynamic Vreman model. Both models showed good overall agreement with available experimental data. It is conjectured that the peak in these fluctuations is caused by an impingement mechanism, in which large eddies, originating in the shear layer, impact the wall just upstream of the mean reattachment location.