Cavitation bubble dynamics near free surface with a half-submerged particle

In this study, a theoretical model is developed and validated experimentally to describe cavitation bubble collapse and jet formation near a half-submerged spherical particle at a free surface. By introducing an anisotropy parameter, the collapse-induced jet, centroid migration, and collapse period of the bubble are quantitatively evaluated as functions of the particle radius and the bubble–particle distance. The main conclusions are summarized as follows: (1) A theoretical criterion for collapse jet modes is established based on the zero-anisotropy parameter, enabling effective identification of jets directed toward the free surface, jets directed away from the free surface, and neutral collapse modes. (2) A scaling law for the bubble centroid migration velocity is further derived, revealing the influence mechanisms of the particle, the free surface, and their coupled effects. (3) A functional relationship among the bubble collapse period, the particle radius, and the bubble–particle distance is established. The prediction function provides a theoretical foundation for controlling cavitation durations by adjusting local boundary geometries.