Experimental Study on Wall Pressure Loading from Interacting Cavitation Bubbles: Effects of Size, Distance, and Collapse Phase

We begin by characterizing the wall pressure loading from a single cavitation bubble collapsing near a rigid wall. The bubble is generated via laser-induced optical breakdown, and high-speed imaging combined with Schlieren visualization provides baseline data on microjet formation and pressure wave dynamics. Building on this, we investigate the collapse behavior of two simultaneously generated cavitation bubbles, with independently controlled size ratios, inter-bubble distances, and relative collapse phases. These parameters are systematically varied to explore their influence on the pressure exerted on the wall. The interactions between the bubbles introduce complex dynamics not present in the single-bubble case. For equal-sized, in-phase bubbles at moderate inter-bubble distance, we observe synchronized collapses suppresses wall pressure due to bubble interactions. In contrast, asymmetric size ratios lead to uneven collapse sequences, resulting in redirected jets and altered pressure signatures. For close inter-bubble distances, coalescence events are observed, producing strong secondary collapse peaks and higher wall pressures compared to isolated bubbles closer to the wall. Time-resolved Schlieren imaging captures both jet and pressure wave evolution, while wall-mounted sensors and distant hydrophones quantify pressure loadings. These findings shed light on the coupled dynamics of cavitation interactions near boundaries and provide new experimental benchmarks for validating multi-bubble collapse models in biomedical and engineering applications.