Collapse of cavitation bubbles near air bubbles

The cavitation erosion is one of the common damage modes in water engineering. The study of the interaction among cavitation bubbles, air bubbles and the wall is of great significance for understanding the mechanism of the air entrainment to alleviate the cavitation and to enhance the cavitation erosion mitigation effect of aeration. By using the high-speed camera, the regular patterns of the collapse of cavitation bubbles in the vicinity of the wall and the air bubbles are studied in this paper. It is shown that in the vicinity of air bubbles, the cavitation bubbles may only collapse towards or from air bubbles, while under the dual impacts of air bubbles and the wall, the direction of collapse of the cavitation bubbles depends on the combined vector of the impact forces of the air bubbles and the wall. When the air bubbles are very close to the cavitation bubbles, the air bubbles will be penetrated and stretched by the cavitation bubbles, when the distance between them is short enough, the cavitation bubbles and the air bubbles will connect to form gas-type cavitation bubbles, and the collapse strength will be significantly decreased, when there are two air bubbles near the cavitation bubbles, they may even be penetrated successively by the cavitation bubbles. Thus it can be concluded that during the air entrainment to alleviate the cavitation, the number of air bubbles is more important than the total air concentration.