A Numerical Study of Collision Efficiencies and Coalescence Parameters for Droplet Pairs with Radii up to 300 Microns

Abstract

Numerical computations of collision efficiencies and certain coalescence parameters are presented for droplet pairs with Reynolds numbers up to 104. This corresponds to radii (for 900 mb, 0C) of up to 300 ?. The superposition principle was used, and the flow fields were computed from the complete nonlinear, time-dependent Navier-Stokes equations, using a modified Rimon's method. The collision efficiencies are mostly geometrical for intermediate ratios of the drops radii, 0.3 < p < 0.7, and exceed the geometric line considerably for high p values. The discussion centers on the validity of the results, as well as their meaning in terms of cloud physics.