The Structure of Turbulent Diffusion : 3rd Report, Study on Two-particle Diffusion and Relative Diffusion

Abstract

To obtain a general understanding for the diffusion of a smoke from a finite-width source in a homogeneous turbulent flow field, the behaviours of the two-particle diffusion and the relative diffusion, as well as the relation between them, were investigated theoretically using a two-particle correlation function. The method proposed in the 1st report was improved to calculate the two-particle diffusion more accurately. Applying the calculated results, it became possible to predict the relative diffusion from a source with an arbitrary concentration distribution. The influence of the width of a uniform source on the coefficient of the relative diffusion was again confirmed to be definite even for an infinite diffusion time, while for the two-particle diffusion the influence of the initial separation was found to vanish in a diffusion time longer than about ten times the integral scale of the turbulence.