The inverse diffusion time scale of velocity gradients in homogeneous isotropic turbulence

Abstract

The diffusion term in the velocity gradient tensor Aij evolution equation in homogeneous isotropic turbulence at moderate Reynolds number has been investigated using full direct numerical simulation (DNS) of the Navier-Stokes equations. This study also considered the diffusion terms associated with the strain rate tensor Sij and the vorticity vector ωi. The statistics of the "diffusion frequency" ω0 defined as ω0= -νΔ2Aij/Aij. which can be thought of as an inverse of a characteristic diffusion time scale t0, has been studied both for diagonal and off-diagonal elements of this tensor, for Sij and for ωi. The probability density functions (PDF's) of the diffusion frequency ω0 for all the varia..