Dynamic Estimation Tests of Decaying Isotropic Turbulence

Abstract

A large-eddy simulation based upon adding estimated, dynamically based backscatter terms to the Smagorinsky subgrid model is shown to be feasible. The model is based upon estimating the subgrid velocity from the high wavenumber aliasing residue of the resolved scale nonlinear terms and the interaction of this estimated velocity with the resolved scales. The objective is to model an intense event in a 256³ direct numerical simulation of decaying flow in a periodic box with random initial conditions before turbulence has developed. Rather than the second order dissipation or enstrophy, higher order norms of the velocity derivative field, the skewness, flatness and peak vorticity, are used to identify the intermittent event. Comparisons with a 256³ DNS truncated to 32³ show that the Smagorinsky model does not capture this event, while the estimation model combined with the Smagorinsky model does. Enstrophy and dissipation around the intense event are also more realistic.