Ball motion and bubble ripples in the interaction of cavitation bubble-elastic ball-curved wall

Abstract

Elastic ball motion and cavitation bubble ripples in cavitation bubble-elastic ball-curved wall interaction was investigated experimentally using single-electrode periodic discharge bubble generation technology and high-speed photography. It was found that the hard ball undergoes a process of “push-pull-push-pull” as the dimensionless bubble-ball distance increases, while the elastic ball undergoes a process of “push-pull” in the same scenario. This is mainly due to the combined effects of the expansion ejection effect, the reverse thrust of liquid jet and the secondary Bjerknes force of cavitation bubble and its rebound bubble, which are strengthened or weakened. The radial vibration of the elastic ball causes a continuous secondary Bjerknes force attraction effect between the ball and the wall, similar to that between an acoustic bubble and a wall. In the interaction of “cavitation bubble-elastic ball-curved wall,” there is a state of equilibrium stability where the centerline of the “bubble-ball” coincides with the centerline of the “bubble-wall.” Both the ball and the bubble will move towards this equilibrium position. This is a result of the three forces with different starting and ending points—the “bubble-wall” secondary Bjerknes force, the “ball-wall” secondary Bjerknes force, and the “bubble-ball” interaction force—reaching a condition of equilibrium. The evolution of the cavitation bubble is usually dominated by toroidal jets, sometimes forming multi-layered nested toroidal jets (annular cylindrical jet). The surface tension waves of the bubble, the elastic modulus waves and the curvature waves of the elastic ball work together to form cavitation bubble ripples. Under the primary intensification of the bubble’s rapid collapse and the secondary intensification of the wall effect, the bubble ripples are reinforced, leading to the formation of multi-layered nested toroidal jets.