Numerical Study of Droplet Generation by Breaking Wind Waves

Breaking waves have been extensively studied numerically, but still, there remains a notable gap in understanding turbulent wind’s impact on wave breaking and sea spray generation. Understanding wind’s role in sea-spray droplet generation is vital for the modeling of heat, mass, and momentum exchange between oceans and marine atmospheric boundary layer. In this study, we employ direct numerical simulation of two-fluid flows to explore the dynamic interplay between wind and breaking waves. To start the simulation, we use a fully developed turbulent wind flow over strongly forced steep waves with the initial wave elevation following a third-order Stokes wave of finite amplitude. The formation of droplets and bubbles from air-sea interactions is accurately captured using the coupled level-set and volume-of-fluid method. By analyzing the instantaneous distribution of spray droplets, we obtain the time history of droplet number and the droplet size spectrum. For a detailed analysis of spray droplets, we implement the optimal network (ON) algorithm for Lagrangian tracking of the droplets efficiently. The ON algorithm provides insights into droplet trajectories and residence times and enables the detection of droplet creation, extinction, fragmentation, and coalescence events.