Reynolds number scaling of particle clustering in turbulent aerosols

Particles with finite inertia in turbulent flow cluster in low-vorticity regions of the fluid due to the inertial imbalance between the denser particles and the lighter surrounding fluid. This effect, sometimes referred to as preferential concentration, has been investigated in several recent numerical studies. Sundaram and Collins (1997 J. Fluid Mech. 335 75) considered the effect of particle clustering on the interparticle collision rate and showed that the radial distribution function, evaluated at contact, precisely corrects the collision kernel for this effect. An open question is how preferential concentration scales with Reynolds number. We investigate this question using direct numerical simulations (DNS). Over the limited range accessible by DNS, it appears that the radial distribution function approaches a plateau with increasing Reynolds number. This contradicts earlier studies that predicted linear growth with Reynolds number. The implications of these findings for very high Reynolds number applications such as cloud formation in the upper atmosphere is briefly discussed.