Time-varying characteristics and influencing factors of the translational motion of bubbles in an ultrasonic field

Abstract The translational motion of bubbles is closely related to the formations of bubble clouds of varying structures and sizes, which is crucial for the distribution of cavitation energy in ultrasonic fields. This paper investigates the time-varying characteristics and influencing factors of the translational motion of bubbles with different initial radii. Our findings indicate that bubbles with identical initial radii exhibit mutual repulsion during their expansion phase and attraction during their contraction phase. For bubbles with different initial radii, they exhibit mutual repulsion during the expansion stage of the larger bubble and mutual attraction during its contraction stage. This behavior indicates that the translational motion of the bubbles ultimately aligns with the radial oscillation of the larger bubble. Furthermore, when one bubble’s initial radius equals the linear resonance radius and the other bubble’s initial radius is larger, the bubbles initially exhibit mutual attraction before transitioning into a uniform translational motion with a constant inter-bubble distance. The two bubbles transition from attraction to repulsion due to the 3rd harmonic resonance effect caused by the increased ultrasonic pressure amplitude. The translational motion of the bubbles can be reversed as the driven frequency approaches the main resonance, the 2nd order harmonic, and the 1/2 order subharmonic resonance frequencies.