An experimental and computational study of bouncing and deformation in droplet collision

An experimental and computational investigation of the collision of equal-sized liquid droplets was conducted. The Navier-Stokes equations for the fluid motion both inside and outside the droplets were solved using the numerical method of "front tracking". The calculated history of the droplet collision process was found to agree well with the experimental results. The configuration of the gas gap between the droplet surfaces was analyzed in order to understand the mechanism which controls droplet bouncing. The minimum gap thickness was found to exhibit a non-monotonic dependence on the droplet kinetic energy, thereby explaining the non-monotonic transition between the collision regimes of coalescence and bouncing. Both computational and experimental results further showed that the droplet collision time is close to its natural oscillation period. Recognizing the large deformation of the droplet surface during collision, large amplitude droplet oscillation with viscous dissipation was also numerically studied.