Droplet size significantly affects impact dynamics yet generating and observing micrometer-sized droplets experimentally is challenging. This study employs a volume of fluid method to simulate droplet normal impact on dry smooth surfaces, investigating the effects of droplet size and surface wettability on impact outcomes and dynamics. By varying the impact velocity, simulations of different impact behaviors were achieved across a range of droplet diameters (50 μm–5 mm) and surface contact angles (50°–165°). The results indicate that on hydrophilic surfaces, increasing impact velocity leads to a transition from deposition to splash. For contact angles greater than 100°, the transition sequence with increasing velocity is from deposition to rebound, and then to splash. Based on numerical simulation, this study refines the existing splashing parameter (K = Re0.25We0.5) model and further establishes mode threshold models for splashing/rebound/deposition under different contact angles. Additionally, the dynamic characteristics of droplet rebound on superhydrophobic surfaces were investigated, including the temporal evolution of kinetic energy, surface energy, gravitational potential energy, and impact force during the impact process. Finally, the influence of contact angle on impact dynamics was examined at constant impact velocities.
Tian et al. (2026) studied this question.