Collapse of a Cavitation Bubble Near an Air Pocket

The dynamics of the cavitation bubble differ depending on the type of boundary near the bubble because the boundary affects the pressure distribution in the vicinity of the bubble. The asymmetric contraction speed of an interface of a collapsing cavitation bubble due to the asymmetric pressure distribution induces a high-speed bubble jet. The cavitation bubble near a rigid solid causes a bubble jet towards the solid surface during the bubble collapse, leading to cavitation erosion on the solid. Recently, a few studies have investigated a gas-entrapping microtextured surface to alleviate cavitation erosion. They confirmed that a bubble jet induced by a collapsing cavitation bubble near air in a pocket directs away from the surface, entrapping the air. In this study, we numerically investigate the hydrodynamic loading on a wall with an air pocket and the alleviation of cavitation erosion by the entrapped air on the solid surface. The presence of an air pocket mitigates the pressure on the wall during the bubble expansion and contraction. However, high pressure is still observed for a small distance between the air pocket and the bubble. The direction of the bubble jet also agrees well with the previous studies, and the tendency of the bubble jet direction is explained by the interaction of the cavitation bubble and the entrapped air in the pocket.