On Conditional Statistics ofthe Diffusion Field of Matter by a Point Source Plume in Uniform Mean Shear Flow

抄録

Various conditional statistics have been examined for the turbulent diffusion of dye solution from a continuous point source in a uniform mean shear flow. The conditional sampling technique consists of two steps: the first step A, which determines the intermittency factor from the probability density function; and the second step B, at which the intermittency function by using a threshold level and a hold time are obtained. It is shown that the transverse profiles of the intermittency factor, the zone-averaged mean concentration and the zone-averaged concentration fluctuation r.m.s. value are all asymmetric about the center line of the plume. The new dimensionless diffusion time η is introduced in terms of the r.m.s. value and the integral length scale of longitudinal velocity fluctuation, and the relative decay rates along η of these conditional statistics on the center line of the plume are estimated and compared with the results in grid-generated turbulent flow.