Stochastic Characteristics of a Point-Source Plume Diffusion Field around a Sphere

Abstract

This paper is the second in a series, which clarifies the effects of flow distortion by a sphere upon the statistical properties of a point-source diffusing plume evolved in grid-generated turbulence. In the preceding paper, only the results along the forward stagnation streamline were given. Here, various data of the entire concentration field around the sphere are investigated. It is found that the conditioned mean concentration is generally constant everywhere but in the recirculated wake region, but the conditioned concentration fluctuation rms values show a slight drop near the surface of the sphere in the nonrecirculating flow region. Moreover, except for the recirculated wake region, the conditioned probability density for near-zero concentration shows a slight drop, while that for the higher concentration increases slightly as the sphere is approached. Furthermore, from analysis of the spectra, the intermittency factor and the probability density distribution, it is concluded that only in the region next to the surface of the sphere have the molecular diffusion fully advanced and the concentration fluctuation dropped to nearly zero.