Kinetic energy recovery and interface hysteresis of bouncing droplets after inelastic head-on collision

Binary collision of unequal-size droplets was investigated numerically by using the front tracking method, with particular emphasis in studying the kinetic energy recovery and the interface hysteresis of bouncing droplets. The numerical results were sufficiently validated against the high-quality experimental data in the literature to verify the quantitative predictivity of the numerical methodology in simulating droplet bouncing. Distinct stages of droplet deformation and viscous dissipation during droplet collision were revealed and explained for their dependence on the Weber number and the size ratio. A linear fitting formula that well correlates the kinetic energy recovery factor of bouncing droplets with various collision parameters was proposed and would be practically useful in modeling inelastic droplet bouncing in Lagrangian spray simulation. As an interesting post-collision characteristic of bouncing droplets, the interface hysteresis was found to favor smaller droplet deformation by decreasing the size ratio or decreasing the Weber number or increasing the Ohnesorge number.