EFFECT OF MOLECULAR DIFFUSIVITY ON TURBULENT-DIFFUSION IN ISOTROPIC TURBULENCE

Dispersion of heat or mass from a point source in homogeneous isotropic turbulence is considered. Molecular diffusion can cause thermal or molecular markers to escape from fluid particles. As a consequence, the contribution of turbulence to the dispersion decreases with increasing molecular diffusivity. This effect is explored by calculating the property autocorrelation for turbulent fields having defined Eulerian space-time correlations. The analysis uses the Corrsin independence approximation and the assumption that the distribution of the particle displacements at some time after release is defined by a Gaussian function.