Analysis of flow structure and air entrainment around a shallowly submerged hydrofoil based on third-generation vortex identification

A shallowly submerged hydrofoil often induces disturbances on the free water surface by generating numerous vortex structures, leading to phenomena such as wave breaking and droplet splashing. These phenomena involve various physical mechanisms. In this study, the third-generation vortex identification technique, Liutex, is employed to perform a detailed analysis of the vortex structures generated by the hydrofoil near the free surface. It is observed that these coherent vortex structures strongly entrain surrounding fluid, resulting in air entrainment and bubble sweep-down phenomena. We analyze the bubble dynamics in terms of bubble number density, volume distribution, and number distribution, revealing the dynamic characteristics of bubbles under the influence of vortex structures. Additionally, by tracking the vortex structures, two distinct forms of air entrainment are identified. The analysis of bubble motion using Liutex demonstrates the evolution and distribution patterns of bubble sizes in the turbulent flow field. The results indicate that the third-generation vortex identification technique, Liutex, effectively explains the mechanisms behind free surface breaking induced by the shallowly submerged hydrofoil.