Effect of preferential concentration on turbulent collision rates

The effect of particle inertia on the interparticle collision rates of a turbulent aerosol was investigated recently by Sundaram and Collins (1997) using direct numerical simulation (DNS). They observed that for values of the particle Stokes number (here defined as the ratio of the particle response time to Kolmogorov time scale) near unity, the collision frequency was enhanced by between one and two orders of magnitude. This enhancement was attributed in part to the local enrichment of the particle concentration in low-vorticity regions of the flow due to the centrifuge effect commonly referred to as preferential concentration (Eaton and Fessler 1994). Sundaram and Collins (1997) showed that the correction factor for the collision kernel in a preferentially concentrated system is g(sigma), where g(r) is the particle radial distribution function and sigma is the collision diameter. This paper uses DNS, in combination with statistical analysis, to study the dependence of the radial distribution function on the turbulence and particle parameters. A curve fit of the results over a broad range of the relevant dimensionless parameters enables easy estimation of g(sigma). The effect of system Reynolds number over the limited range accessible by DNS is also presented. In general, the degree of preferential concentration increases with increasing Reynolds number. (C) 2000 American Institute of Physics. [S1070-6631(00)51010-1].