Effect of preferential concentration on turbulent collision rates

The effect of particle inertia on the interparticle collision rates of a tu rbulent aerosol was investigated recently by Sundaram and Collins (1997) us ing 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 enh anced by between one and two orders of magnitude. This enhancement was attr ibuted in part to the local enrichment of the particle concentration in low -vorticity regions of the flow due to the centrifuge effect commonly referr ed to as preferential concentration (Eaton and Fessler 1994). Sundaram and Collins (1997) showed that the correction factor for the collision kernel i n a preferentially concentrated system is g(sigma), where g(r) is the parti cle radial distribution function and sigma is the collision diameter. This paper uses DNS, in combination with statistical analysis, to study the depe ndence of the radial distribution function on the turbulence and particle p arameters. A curve fit of the results over a broad range of the relevant di mensionless parameters enables easy estimation of g(sigma). The effect of s ystem Reynolds number over the limited range accessible by DNS is also pres ented. In general, the degree of preferential concentration increases with increasing Reynolds number. (C) 2000 American Institute of Physics. [S1070- 6631(00)51010-1].