On the magnitude of the subgrid scale eddy coefficient

Abstract

Three-dimensional numerical integrations capable of resolving the energy containing motions at large Reynolds number have tested the nonlinear eddy-viscosity formulation in the two cases when the turbulence is generated by mean shear or by thermal instability. The proportionality constant suggested by Lilly is found to be applicable in the latter case, but a smaller value is found necessary in the presence of mean shear. Spectra of calculated velocity components are shown to deviate from a k 5/3 law, as k approaches the grid cutoff wavenumber, in a manner consistent with the application of Reynolds-averaging over grid volumes.