Cavitation characteristics near the wall in the presence of an attached preset air bubble

This study experimentally investigates the dynamic behavior of a cavitation bubble near a solid wall in the presence of an attached preset air bubble, and the effect of boundary interactions on jet formation and collapse dynamics is emphasized. Since the dynamic characteristics of the cavitation bubble would be affected by both the solid wall and the free surface of the preset bubble, the effects of the dimensionless radius ratio (γr) and distance (γs) are systematically studied. It is found that the dynamic process of the cavitation bubble and the preset bubble is interacting, and the presence of the preset bubble can effectively weaken the influence of the solid wall on the collapse process. In addition, the local jets in the opposite direction may be induced within the two bubbles due to the strong interaction between them, and the strong and weak interaction criteria are given based on the existence of the local jet. Additionally, the rebound direction of the cavitation bubble is changed with different γs and γr; therefore, a synthetic direction factor (ζ) is introduced to illustrate the combined effect of both the preset bubble and the solid wall. Then, the distribution of different modes of the first rebound of the cavitation bubble is divided based on the value of ζ, and an overall phase diagram is provided. These basic understands of the relationship between bubble dynamic mode and different boundaries might offer potential strategies for reducing cavitation-induced damage and optimizing industrial applications.