A lattice Boltzmann study on the bouncing behavior of equal-sized droplet collision

The bouncing behavior of equal-sized droplet collision is simulated by the recent multiphase lattice Boltzmann model with self-tuning equation of state. The nonmonotonic coalescence-bouncing-coalescence transition is successfully reproduced. The effects of Weber number, Ohnesorge number, liquid-to-gas density ratio, and impact factor are investigated. It is found that when the Reynolds number or Ohnesorge number is fixed, the nonmonotonic coalescence-bouncing-coalescence transition can be observed as gradually increasing the Weber number. The increase in the Ohnesorge number is beneficial to the occurrence of the bouncing behavior and leads to the increase in the largest Weber number for the bouncing behavior. The lowest Ohnesorge number for the bouncing behavior is approximately 0.2. Considering that the bouncing behavior is caused by the resistance effect of the gas film between droplets, the decrease in the liquid-to-gas density ratio can promote the bouncing behavior and thus expand the range of the corresponding Weber number. For the off-center collision, the increase in the impact factor can trigger the coalescence-bouncing transition under both relatively small and large Weber numbers. For the coalescence-bouncing transition with a relatively large Weber number, the phase diagram of the collision outcome is in qualitative agreement with the prediction by the previous theoretical model.