Wall vortex induced by the collapse of a near-wall cavitation bubble: Influence of the water surface

Abstract

Wall vortex occurs when a cavitation bubble oscillates far from a single rigid wall (at a dimensionless standoff distance \ensuremath{\gamma}${}_{r}$>1.3). This study finds that a wall vortex in an expanded new regime forms instead of a free vortex at a smaller \ensuremath{\gamma}${}_{r}$ value, when introducing a water surface. Criteria for vortex flow patterns are proposed based on the direction of the bubble centroid migration at the beginning of the second cycle ${t}_{c}$ though a theoretical model developed with a Lagrangian formulation. Numerical analysis reveals that the wall vortex flow with the influence of the water surface contributes to a greater wall shear stress and larger area, thus increasing the surface cleaning potential.