Experimental analysis of particle dynamics influenced by cavitation bubbles near a rigid wall

This study utilized experimental methods involving high-speed cameras to observe the interaction between cavitation bubbles, generated by a low-voltage electric spark device, and particles near a rigid wall. The dynamic characteristics of the particles were analyzed under varying conditions, including different cavitation bubble sizes, particle sizes, and distances between the cavitation bubble and the wall. Two characteristic parameters were introduced: χ for the particle and cavitation bubble sizes, and λ for the cavitation bubble wall distance. Qualitative distinctions were made among types of particle–bubble interactions, and force analysis was conducted under conditions where χ exceeded the threshold χt. The findings reveal that when χ < χt, particle motion is primarily influenced by the jet effects produced by the cavitation bubble. Conversely, when χ > χt, particle motion is dominated by the radiation forces exerted by the cavitation bubble. Under jet-dominated conditions, particle trajectories were observed to be erratic and unpredictable. For cases where λ < 0, the high-speed jet directly impacts the particle. Conversely, for λ > 0, the jet's velocity decays rapidly upon reaching the particle. In scenarios dominated by radiation forces, the cavitation bubble drew particles away from the wall, followed by their free fall back toward it. The influence of gravity, buoyancy, bubble radiation force, fluid resistance, and virtual mass force on particles was studied when radiation forces prevailed. The acceleration formula for particles was derived through the application of the bubble dynamics equation and was refined based on experimental observations.