Direct Numerical Simulation of Homogeneous Anisotropic Decaying Turbulence with Heat Transport.

Abstract

Budgets of turbulent heat flux and temperature variance were calculated by means of direct numerical simulations of the return-to-isotropy process of decaying homogeneous turbulence on 963grid points. The process was simulated for different sets of anisotropic initial conditions. In each case, a constant mean temperature gradient was imposed in one direction. The mechanism of isotropization and its effects on the turbulent statistics were investigated. It was found that the rate of isotropization should be affected by the sign of the third invariant of the stress anisotropy tensor, and is faster when the third invariant is negative. The isotropization of vorticity and dissipation tensors proceeds more rapidly than that of the Reynolds stress tensor. When the turbulence Reynolds number is relatively small, as in the present study, the anisotropy of Reynolds stress has a vigorous effect on the directional dissipation components of temperature fluctuation and turbulent heat flux ; the temperature gradient becomes larger in the direction in which the velocity fluctuation is smaller than in the other directions. The ratio between the pressure scalar gradient correlation and the dissipation of turbulent heat flux also should be affected.