Dynamics of High-Speed Raindrop-Surface Interactions in Oceanic Precipitation

Rainfall over the ocean plays a significant role in the global fresh water cycle, heat exchange between the ocean and atmosphere, modulation of ocean waves, and the generation of sprays and aerosols. The interaction between raindrops and the ocean surface is highly transient and complex, making the hydrodynamics of such events difficult to resolve, especially when the terminal velocity of the raindrops is high. This study numerically investigates the impact of two raindrops on a liquid pool, focusing on how their interaction influences interfacial dynamics and secondary droplet formation. We perform direct numerical simulations using the volume-of-fluid method with adaptive mesh refinement to accurately capture fluid interfaces while maintaining computational efficiency. In our simulations, the raindrops are initialized above the free surface with velocities representative of raindrop impacts. The numerical framework is first validated against established experimental and numerical results for single-raindrop impacts. From the simulations of two-raindrop cases, we identify a critical influence of the distance between the raindrops on the flow physics, including cavity evolution and central film disintegration. These interactions are found to profoundly affect the generation of secondary droplets.