Abstract
Experimental examination has been made of the disturbance effect of a circular cylinder on the diffusion process of a dye solution by a non-buoyant plume from a point source in grid-generated water turbulence. This paper is mainly associated with the characteristics of the fluctuating concentration field upstream of, around, and behind the cylinder. The results for the velocity and mean concentration fields have been already reported in ref. [1]. The interesting result upstream of the cylinder is that the concentration fiuctuation r. m. s. values on the plume axis (i. e. the stagnation line) show a rapid decrease near the stagnation point. This is because the turbulence distortion by the cylinder promotes the mixing of matter. The data behind the cylinder show that the vertical profiles of r. m. s. values have double-peaks and their center-line r. m. s. values obey the hyperbolic decay law in the downstream direction. Further, as in the mean concentration field, the vertical and horizontal profiles of r. m. s. values appear to be nearly similar behind about 20 diameters from the cylinder.
