“Soft” and “Hard” merging of head-on colliding droplets

Numerical simulation of sprays and spray combustion requires quantitatively predictive subgrid models for droplet collision and its outcomes. The dynamics of head-on merging between two equal-size droplets was numerically investigated, with emphasis on studying the collision dynamics before the occurrence of droplet merging. Front tracking method was adopted to simulate the “soft” and “hard” merging dynamics of previous experiment with transition collision Weber number, while Volume of Fluid simulation was also employed for comparison. Numerical results were sufficiently validated against the experimental shadowgraphs. Four distinct stages of vortex evolution were observed and explained according to the numerical results. Viscous dissipation was found to substantially influence the vortex dynamics, increasing of Oh promotes viscous dissipation hence results in the decreasing of the vorticity.