Millimeter-scale splash-droplet generation and transport in plunging breaking waves

Plunging wave breaking ejects millimeter-scale liquid fragments through jet impact, splash-sheet rupture, ligament pinch-off, and secondary splashing. The short-time evolution of this resolved splash component remains difficult to quantify because generation, deformation, transport, and reentry occur concurrently. In this study, high-fidelity three-dimensional interface-resolving simulations with adaptive mesh refinement are used to examine the generation and short-time transport of millimeter-scale splash droplets during plunging breaking. Droplet production develops over three event-defined stages: overturning and impact onset, active splash fragmentation, and wake-dominated decay. The primary jet impact produces liquid sheets, ligaments, and relatively large droplets under strong inertial loading. After the coherent splash collapses, additional resolved droplets arise from the continued breakup of residual sheets, ligaments, surface-connected liquid structures, and secondary re-impact. The resolved size distributions exhibit clear stage dependence, but no universal power law or distinct fragmentation-regime transition is inferred because the accessible scale range is limited and its lower end is resolution sensitive. The representative trajectories indicate stronger inertial memory for larger droplets and greater short-time wake modulation for smaller resolved droplets. Larger droplets follow predominantly arch-like paths and return rapidly toward the free surface, whereas smaller resolved droplets show stronger short-time modulation by the unsteady wake without behaving as passive tracers. The conclusions are restricted to the quantitatively retained millimeter-scale splash-droplet population. Micron- and submicrometer-scale film and jet droplets produced by bubble bursting, together with evaporation and long-range atmospheric transport, are not resolved.