A Stochastic Backscatter Model for Grey-Area Mitigation in Detached Eddy Simulations

A new stochastic backscatter model is proposed for detached eddy simulations that accelerates the development of resolved turbulence in free shear layers. As a result, the model significantly reduces so-called grey areas in which resolved turbulence is lacking after the computation has switched from a Reynolds-averaged Navier-Stokes simulation to a large eddy simulation. The new stochastic model adds stochastic forcing to the momentum equations with a rate of backscatter from the subgrid to the resolved scales that is consistent with theory. The effectiveness of the stochastic model is enhanced by including spatial and temporal correlations of the stochastic forcing for scales smaller than the cut-off scale. The grey-area mitigation is demonstrated for two canonical test cases: the plane free shear layer and the round jet.