Droplet impact on waves: jetting dynamics

When a droplet impacts a liquid surface, its kinetic energy is transferred into surface deformation, producing a cavity that subsequently collapses and may generate a vertical jet. This jetting process, which can lead to the formation of secondary droplets, has been extensively studied in the literature for droplet impact on quiescent liquid surfaces. However, the influence of dynamic and moving liquid surfaces, such as waves, remains poorly understood. Yet, the impact of raindrops on ocean waves and the resulting jetting can significantly influence air-sea exchange and the generation of sea spray. To address this knowledge gap, we perform controlled laboratory experiments using a bench-top wave tank and high-speed imaging to investigate droplet and wave interactions. Droplets are released with controlled height and size to impact the wave surface at different phases, with impact dynamics characterized by the Weber number. We quantify the cavity evolution, jetting process, and breakup behavior across a range of impact conditions. Our findings reveal that the phase of the underlying wave at the moment of impact strongly modulates the cavity geometry, which in turn governs jet formation and fragmentation. We further identify scaling relations, providing new insights into the physics of droplet impact on unsteady liquid surfaces.