Cushioning effect of a gas pocket on bubble jet mitigation near solid

Abstract

A cavitation bubble collapsing near a boundary causes a liquid jet because of the asymmetric pressure distribution near the bubble. The characteristics of a liquid jet induced by a collapsing bubble depends on the boundary near the bubble. Previously, a study confirmed that the liquid jet near the Gas Entrapping Microtextured Surface(GEMS) is directed away from a solid surface. In this study, we numerically investigate the mitigation of the pressure on a solid surface with a single circular-cylindrical-shape air pocket by varying the geometric parameters, such as a pocket radius and a depth. The simulation is conducted on the open source software OpenFOAM with PISO algorithm. The interaction of a bubble and an air pocket is analysed by dividing the process into the bubble expansion stage, bubble contraction stage, secondary bubble expansion stage. In most cases, the bubble jet is directed away from the air pocket. Moreover, the maximum pressure on the boundary decreases contrary to the solid surface without an air pocket. These results are explained successfully by the interaction of the cavitation bubble with the air pocket.