Dynamics of cavitation bubbles near two perpendicular walls

What is it about?

The behaviour of a laser-induced cavitation bubble near two perpendicular rigid walls and its dependence on the distance between bubble and walls is investigated experimentally. It was shown by means of high-speed photography with 100000 frames/s that an inclined jet is formed during bubble collapse and the bubble migrates in the direction of the jet. At a given position of the bubble with respect to the horizontal wall, the inclination of the jet increases with decreasing distance between the bubble and the second, vertical wall. A bubble generated at equal distances from the walls develops a jet that is directed in their bisection. The penetration of the jet into the opposite bubble surface leads to the formation of an asymmetric toroidal bubble that is perpendicular to the jet direction. At a large distance from the rigid walls, the toroidal bubble collapses in the radial direction, eventually disintegrating into tiny microbubbles. When the bubble is in contact with the horizontal wall at its maximum expansion, the toroidal ring collapses in both radial and toroidal directions, starting from the bubble part opposite to the vertical wall, and the bubble achieves a crescent shape at the moment of second collapse. The bubble oscillation is accompanied by a strong migration along the horizontal wall./

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Why is it important?

Our study is a step towards understanding the interaction of cavitation bubbles with rigid walls in 3D configurations. The present experimental observations reveal fundamental aspects of the behaviour of cavitation bubbles near two perpendicular rigid walls, which can be used as a basis for future experimental, theoretical and numerical investigations on the dynamics of cavitation bubbles, associated flow field and mechanisms of cavitation erosion in similar configurations. In particular, numerical simulations that are able to cover a large part of the rebound phase of the bubble become essential for a better understanding of the complicated dynamics of the toroidal bubble. Beyond its fundamental significance, this study may have important implications for cavitation-mediated cleaning of rigid surfaces and can potentially introduce a new method for controlling the direction of the liquid jet and the subsequent behaviour of the vortex ring developed during bubble collapse.