Modeling Binary Droplet Collision at High We

In high-speed sprays, atomization depends strongly on how droplets break up and collide. The outcome of a collision controls droplet size distribution, velocity fields, and how liquid mass spreads in different directions. These factors are important for spray modeling, but predicting secondary droplet formation under high Weber number (We) conditions is still difficult. In this study, we use Smoothed Particle Hydrodynamics (SPH) to simulate binary droplet collisions up to We =1500 and varying impact parameters. The simulations capture the onset and growth of shattering while breakup diameters, satellite formation, and overall shapes show good agreement with experiments. A new regime map is constructed using the simulation results. Traditional regimes such as bouncing, coalescence, reflexive separation, and stretching separation are reproduced for We below 100. At high We, three additional regimes are identified: fingering separation, shattering separation, and a combined stretching–shattering separation. Sauter mean diameter (SMD) and droplet mass distribution are studied to assess the impact of collisions on the resulting spray field. Separate SMD values are computed for droplets moving in different directions, along with the fraction of mass carried in those directions. This directional analysis provides insight into how binary collisions redistribute liquid mass and momentum under varying impact conditions. Overall, this work shows that SPH can capture both the general features and quantitative trends of droplet collisions at high We. The outcomes are relevant to high-speed sprays, combustion processes, and multiphase flows where droplet collisions at high We play a dominant role.