Simulation of scalar mixing by stationary isotropic turbulence

Abstract

A closure model at the two-point probability density function level is proposed, and numerically solved, for the case of passive scalar mixing in stationary isotropic turbulence. It is found that the ratio of the initial scalar microscale to the velocity microscale, λφ)0/λ, in the range 0.56–2.97, has little effect on the scalar decay rate when the initial scalar-to-velocity integral length scale ratio, Lφ)0/L, is roughly fixed at 2.0. On the other hand, when λφ)0/λ is fixed at 1.97 the ratio Lφ)0/L is found to have a significant effect on the scalar decay rate. These results mimic those from earlier direct numerical simulation (DNS) calculations, but at an accelerated time scale. The mechanical-to-scalar time scale ratio, which in stationary turbulence is inversely proportional to λ2φ, has the same asymptotic value as was reached in DNS and has the same dependence on initial conditions.