On demand controlling of cavitation bubble collapse and jet formation through a free and rigid boundary arrangement

Cavitation bubbles during their collapse may form fast microscopic jet flows directed either towards a rigid boundary or away from a free surface. Here, we demonstrate experimentally that the jetting direction of a cavitation bubble near the opening of a partially liquid-filled capillary can be controlled by a non-dimensional stand-off distance, which is a function of the bubble position, capillary radius, and liquid filling. The bubble radial dynamics in the experiments are reproduced with a modified Rayleigh equation, and the full flow field is simulated with the compressible Volume-of-Fluid method. Particularly interesting cases are the neutral collapses that show either spherical symmetric flows where the partially liquid-filled capillary becomes hydrodynamically invisible to the cavitation bubble, or a torus bubble upon minimum volume, which demonstrates shock wave amplification and is similar to the one observed near a rigid boundary.