Flow characteristics and bubble statistics during the fragmentation process of the ingested main cavity in plunging breaking waves

Plunging breaking waves play an important role in the exchange of heat, momentum, and mass between the atmosphere and ocean. In this paper, a series of direct numerical simulations is conducted to investigate the fragmentation process of the ingested main cavity in plunging breaking waves. The two-phase Navier-Stokes equations are solved using the finite-volume method based on adaptive refinement meshes. The free surface is captured using a geometrical volume of fluid method. Both 2-D, 3-D simulations are conducted. Instantaneous flow fields at different stages of wave breaking are presented and quantitative analysis for bubbles is performed. The 2-D instantaneous vorticity field and local velocity field are visualized to discuss the general flow characteristics during the fragmentation process. Then a 2-D parametric study is conducted to investigate the differences in the flow characteristics during the fragmentation process under different wave parameters including initial wave steepness (ε), Bond number (Bo), and Reynolds number (Re). 3-D vortex structures are shown to further investigate the mechanisms behind the differences in the flow characteristics. The bubble size distributions under two different initial wave steepness are also discussed with their relationship to the fragmentation process of the ingested main cavity. This research offers a significant understanding of the distinct procedures and fundamental dynamics involved in wave breaking, enhancing our comprehension of this intricate event.