Numerical study of air entrainment mechanisms and vortical structures in breaking waves

Wave breaking is a highly nonlinear, multi-scale gas–liquid phenomenon with critical implications for ship performance and the prediction of bubbly flows around vessels. This study employs a high-fidelity numerical approach based on adaptive mesh refinement, combining the CLSVOF interface-capturing method with the Liutex-Omega vortex identification technique, to systematically investigate three representative types of breaking waves: spilling, weak plunging, and strong plunging breakers. The research focuses on classifying and analyzing air entrainment mechanisms, characterizing the statistical properties of bubbles and droplets, which include volume, number, and size distribution, across different stages, and revealing the formation and evolution of complex vortex structures. The results show that plunging breakers exhibit multiple air entrainment types, including jet-impact entrainment, backward-splash entrainment, splash-impact entrainment, leading-edge entrainment, and turbulent entrainment, while spilling breakers involve only the latter two mechanisms. Droplet sizes follow a power-law distribution with an exponent of approximately −4.5, and bubble sizes conform to a −10/3 power law. Strong plunging breakers generate significantly more droplets and bubbles than the other types. Jet-impact entrainment induces spanwise vortex tubes and streamwise ring-like vortices through rotational deformation, while splash-impact and leading-edge entrainment generate hairpin vortices analogous to those observed in turbulent boundary layers. Vortices associated with turbulent entrainment exhibit wide spatial coverage and relatively weak intensities. This work not only provides a systematic characterization of entrainment and vortex dynamics but also delivers extensive quantitative datasets of bubbles and droplets, offering valuable references for developing physics-based bubble models for ship-induced bubbly flows.