A new flow simulation methodology applied to the turbulent backward-facing step

For the flow simulation methodology (FSM) of Speziale and Fasel, turbulent stresses and heat fluxes are computed using a state-of-the-art RANS turbulence model, but where the model contribution is scaled according to a contribution function which depends on the physical resolution of the computation. In flow regions (and instants of time) with high physical resolution only the smallest (unresolved) scales of motion are modelled while the larger structures are computed directly (similar to LES), whereas in regions of very coarse resolution an unsteady RANS simulation is recovered. The methodology thus may be classified as a RANS-LES hybrid or better, a unified approach to RANS and LES. In order to evaluate the potential of this methodology, it is applied to the unsteady flow over a backward-facing step at Re_H = 3000 and Ma = 0.25, with laminar separation and turbulent reattachment. The results are compared to DNS, LES, and unsteady RANS.