Study on the coupling characteristics of different numbers of cavitation bubbles and particle groups in the free domain

In a free field multiphase environment, the coupling between cavitation bubble dynamics and particle groups can markedly reshape local flow structures and thereby influence particle impact risks. Within a unified dimensionless framework, this study investigates three representative systems-single cavitation bubble, double cavitation bubble, and three cavitation bubble-by combining experimental observations, theoretical analysis, and three-dimensional numerical simulations to systematically characterize the evolution of particle-group velocity magnitudes and directions. The results show that, for a single cavitation bubble, the maximum particle velocity decays significantly with increasing dimensionless distance, and the velocity direction points outward from the bubble center during expansion but reverses toward the center during collapse. For a double cavitation bubble, the particle response in the superposition region differs distinctly from that in the outer-side regions: when particles are located near the centerline connecting the bubble centers, the collapse-induced microjet can trigger peak acceleration events, with representative particle velocities reaching the order of 60-70 m/s, far exceeding those dominated by radiation pressure; meanwhile, the particle velocity direction in the superposition region can become approximately perpendicular to the centerline. For a three cavitation bubble, particle-group responses are highly sensitive to the configuration and the relative inter-bubble spacing parameters: symmetric configurations tend to exhibit more collective responses, whereas asymmetric or non-collinear configurations enhance the spatial expansion and dispersed contributions of the superposition region. Group-level statistics further indicate that multi-bubble systems can substantially strengthen y-direction momentum exchange, and a set of group metrics reveals systematic changes in contribution patterns and the dominant affected range. These findings clarify the region-dependent dominance of radiation pressure and microjet impact in cavitation bubble-particle groups coupling, providing reproducible quantitative evidence for particle impact assessment in multiphase systems.