Numerical investigation of splash modes and mechanisms for tiny droplet oblique impact on a dry smooth surface

The deposition and splashing behavior of 50 μm droplets impacting a dry smooth surface at angles ranging from 10° to 90° was investigated through numerical simulations with the volume of fluid method. A contact angle of 90° (indicating neutral wettability) was maintained for all simulation cases. Splash characteristics were systematically examined as functions of impact angle and velocity. At low impact velocities, droplets were observed to deposit on the surface, either without breakup or with partial breakup. In contrast, higher impact velocities produced splashing regimes characterized by two distinct modes: rim-breakup splashing and bulge-rebound splashing. In the rim-breakup mode, the inertia of the rapidly spreading lamella causes the rim to split and break apart, generating many small, dispersed secondary droplets within a limited azimuthal range. Conversely, in the bulge-rebound mode, the bulge formed at the lamella's leading edge rebounds outward, releasing a large secondary droplet. Furthermore, the boundary between deposition and splash was determined. It was found that rim-breakup splashing is strongly correlated with the droplet's initial normal velocity component, whereas the critical velocity for bulge-rebound splashing decreases as the impact angle decreases. Finally, the mechanisms of these two splashing modes were analyzed.