Numerical Simulations of Three-Dimensional Drop Collisions

Three-dimensional simulations of the off-axis collisions of two drops are presented. The full Navier-Stokes equations are solved by a front-tracking finite difference method that allows a fully deformable fluid interface and the inclusion of surface tension. Depending on whether the interface between the drops is ruptured or not, the drops either bounce or coalesce. For drops that coalesce, the impact parameter, which measures how far the drops are off the symmetry line, determines the eventual outcome of the collision. For small impact parameters the drops coalesce permanently, but for larger impact parameters a grazing collision, where the drops coalesce and then stretch apart again, is observed. The numerically found boundary between coalescing and grazing collisions is compared with experimental observations.