Jetting of a near-wall cavitation bubble induced by another tandem bubble

Double bubbles near a rigid wall surface collapse to produce a significant jet impact, with potential applications in surface cleaning and ultrasonic lithotripsy. However, the dynamic behaviors of near-wall bubbles remain unexplored. In this study, we investigate the jetting of a near-wall bubble induced by another tandem bubble. We define two dimensionless standoff distances, γ₁, γ₂, to represent the distances from the center of the near-wall bubble to the rigid wall and the center of controlling bubble to the center of the near-wall bubble, respectively. Our observations reveal three distinct jetting regimes for the near-wall bubble: transferred jetting, double jetting, and directed jetting. To further investigate the jetting mechanism, numerical simulations are conducted using the compressibleInterFoam solver in the open-source framework of OpenFOAM. A detailed analysis shows that the transferred jet flow is caused by the pinch-off resulting from the axial contraction velocity at the lower end of the near-wall bubble being greater than the vertical contraction velocity, leading to a maximum jet velocity of 682.58 m/s. In the case of double jetting, intense stretching between the controlling bubble and the wall leads to a pinch-off and a double jetting with a maximum velocity of 1 096.29 m/s. The directed jet flow is caused by the downward movement of the high-pressure region generated by the premature collapse of the controlling bubble, with the maximum jet velocity reaching 444.62 m/s.