Statistical properties of the diffusion of matter by a non-buoyant plume in grid-generated turbulence.

The statistical properties of the concentration field have been investigated by using the conditional sampling technique in a turbulent diffusion of dye solution by a non-buoyant plume in grid-generated water turbulence. The radial profiles of the zone-averaged mean concentration and concentration fluctuation r.m.s. value appear to be nearly similar, and the values of these properties and the intermittency factor on the center line of a plume decay as hyperbola in the downstream direction. Stochastic properties of the detecting process of concentration have been examined. the detecting process is found to be approximated well to the Poisson process only in the outer edge region of a plume. In order to specify the spatial situation of the diffusion field, the radial and axial variations of probability density functions for the thickness of diffusing layers and the distance between the adjoining two layers are also investigated.