The disturbance effect of a circular cylinder on the diffusion of matter by a plume from a point source in grid-generated turbulenec. (3rd report. Characteristics of the conditional statistics).

Abstract

The effect of the disturbance of a circular cylinder on the diffusion process of matter from a continuous point source in grid-generated water turbulence has been investigated experimentally. In this paper, the characteristics of the conditional statistics are mainly examined and compared with the results concerning the mean and fluctuating concentration field reported in the previous papers. The data downstream of the cylinder show that the vertical profiles of the conditionally-averaged mean concentration in plume show near constancy in the extensive region containing the plume axis, and those of the conditionally-averaged concentration fluctuation rms value have double peaks .The auto-correlation coefficients of the intermittency function behind the cylinder have apparent periodicity, and this suggests that meandering of the plume is caused by the Karman vortex. On the plume centerline, it is found that the conditional relative intensity decreases downstream by the disturbance effect of the cylinder, whereas that without the cylinder does not change downstream.