Stochastic Backscatter for Grey-Area Mitigation in Hybrid RANS-LES Simulations

A scale-resolving simulation methodology that includes stochastic energy backscatter is incorporated into a proprietary block-structured compressible flow solver. Particular attention is devoted to the discretisation of the convective terms in the averaged/filtered governing equations. The objective is to achieve satisfactory dissipation and dispersion properties, while minimising the number of modifications to be made to the existing RANS solver, which employs, by default, a second-order accurate central scheme with Jameson-Schmidt-Turkel scalar artificial dissipation. A novel blending strategy, combining non-dissipative and strongly dissipative numerical discretisations, is proposed to enhance the overall numerical stability. First of all, the model is calibrated using the classic decay of isotropic homogeneous turbulence. Then, its effectiveness in mitigating the grey area is shown through the simulation of the mixing co-flow between the wake originating downstream of an airfoil at zero angle of attack and the zero-pressure-gradient turbulent boundary layer developing over a flat plate.