Stochastic backscatter in a subgrid-scale model: Plane shear mixing layer

Abstract

The traditional Smagorinsky subgrid‐scale viscosity (C Sλ)2 S has been supplemented by the addition of stochastic backscatter. The random acceleration is derived from a vector potential C b ‖S δt‖3 / 2(λ/δt)2 g. Here S is the local strain rate, λ is the grid resolution length scale, δt is the time step, and g is a unit random Gaussian. It is found that values C S=0.2 for the Smagorinsky constant and C b =0.4 for the backscatter constant give a robust calculation of the two‐dimensional shear mixing layer with the observed growth rate and with realistic emergence of random coherent eddy structures.