Characteristics of a laser-induced bubble near the wedge between the gas–liquid interface and solid wall

The dynamics of cavitation bubbles near the wedge region between the free surface and solid wall were experimentally studied using a high-speed camera. In the experiments, the wedge region had different angles θ depending on the solid surface's hydrophobicity. Additionally, the standoff distances of the bubble-solid wall (λw) and bubble-free surface (λs) were varied. Several intriguing results were obtained. First, a competitive mechanism between the free surface and the solid wall during the collapse was observed: the influence of the free surface on the bubble occurred earlier than that of the solid wall. As the collapse progressed, the influence of the solid wall increased. The ratio of the free surface-induced pressure gradient (FPG) to the solid wall-induced pressure gradient (SPG) at the end of the collapse determined the jet direction. Second, altering θ appeared to have minimal influence on the relative ratio (s) between FPG and SPG during bubble collapse. In contrast, variations in λw and λs significantly affected the changing of s, leading to distinct bubble collapse dynamics at varying standoff distances. Finally, the synergistic effects of θ and standoff distances on the jet direction were quantitatively and systematically studied. The distribution of different scale jets was divided based on the value of ζ (Kelvin impulse), and an overall distribution map was provided. This fundamental understanding of the interaction between bubble dynamics and complex boundaries may offer strategies for improving ultrasonic cleaning and reducing cavitation erosion.