An improved diffusion model for second-moment closures derived from zero-mean-shear turbulence
Abstract (summary)
An examination of diffusion modelling in second-moment turbulence closures is presented. The main objectives of the present work are to gain a better understanding of the processes that are grouped into the net diffusive transport of Reynolds stresses, $D\sb{ij}$, and to develop an improved model for $D\sb{ij}$. The benchmark case of zero-mean-shear turbulence is used as a guide in this study. The analysis of zero-mean-shear turbulence shows that the pressure-velocity processes in $D\sb{ij}$ play a central role in establishing the anisotropy level in diffusive turbulence. Existing models for $D\sb{ij}$ based solely on the triple velocity correlation are shown to be inadequate in the diffusive limit. The improved $D\sb{ij}$ model is formulated to account for the pressure-velocity processes, and to be exact in the diffusive limit. The present validation verifies the integrity of the improved model, and shows that including he influence of the pressure-velocity processes in a $D\sb{ij}$ model extends the model's range of applicability from the diffusive limit to situations where diffusion is much less important.