This paper aims to reveal the influence of a rigid wall with a gas entrapping hole on the characteristics of the dynamic behavior of a laser-induced bubble collapse. A high-speed camera system was used to record the oscillation process of the laser-induced bubble on a rigid wall with a gas entrapping hole. When a bubble is generated by a laser above the wall with a gas entrapping hole, the entire bubble collapse stays away from the wall or splits into two bubbles because of a radial jet induced by bubble contraction. These two distinctive collapse modes are dependent on the distance between the wall and the bubble. The focus of this study is the quantitative analysis of the jet formation, bubble migration, and oscillation period, and compared with the behavior of the bubble near a rigid wall. The results show that unlike the generation of the bubble near a rigid wall, a rigid wall with a gas entrapping hole affects the morphology of the jet and changes the direction of migration of the bubble, and decreases the oscillation period. Thus, the rigid wall with a gas entrapping hole could be effective for reducing cavitation erosion on the wall surface, which is supported by our experiment results.

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The objective of this paper is to reveal the influence of different surface geometric conditions on the dynamic behavior characteristics of a laser-induced bubble collapse. A high-speed camera system was used to record the oscillation process of the laser-induced bubble on plane solid walls with different roughness and a wall containing reentrant cavities full of water or gas. The focus is on the quantitative analysis of the morphological characteristics of the cavitation bubble near the solid wall under different surface forms during the first two oscillation period. The results show that the dimensionless ratio γ, defined as the distance from the center of the bubble to the wall divided by the maximum radius of the bubble, has a great influence on the change of the cavitation shape in the direction of the vertical wall. Different surface geometries without gas in our cases have no significant effect on the collapse time of cavitation bubbles. While for the surface containing gas, the direction of movement of the bubble accompanying the micro-jet will greatly change during the collapse of the cavitation bubble, and the collapse time seems to be independent of the dimensionless ratio γ. These achievements shed the light for the engineering to avoid the damage of the micro-jet caused by design suitable surface geometry.

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