Manipulation of the collapse direction of the cavitation bubbles near the boundary with attached gas plastron

This paper studies the collapse of spark-charged bubbles on hydrophobic surfaces to which a gas plastron (gas layer) adheres. Through high-speed imaging, bubbles appear as jets toward the wall, neutral jets, and jets away from the wall, respectively, with the increase in the equivalent thickness of the gas layer. Via numerical analysis, it is found that the air bubble array (with different bubble radii) on the wall, which is equivalent to a gas plastron at a hydrophobic wall surface, produces the same phenomenon as the experiment, and the dynamic behavior characteristics of the experiment and simulation are very consistent. It is further found that the drag reduction effect of the gas plastron on the wall and the bubbles' fluctuation together determine the jet's direction. This work gives the primary factors influencing the jetting directions of the bubbles above a gas-entrapped hydrophobic surface and provides a new perspective for the design of the gas-entrapping hydrophobic surface to prevent cavitation erosion.