Formation mechanism and evolution properties of double jets induced by cavitation bubble pair

Interactions between bubbles are prevalent in cavitation flow within fluid mechanics. This study develops a Kelvin impulse model suitable for a bubble pair and conducts extensive high-speed photographic experiments to investigate the dynamic properties of the double jets induced by the bubble pair in a free-flow field. The effects of key parameters, such as the phase difference and radius ratio of the bubble pair, on the variations in jet intensity and direction are quantitatively evaluated, and the parameter ranges corresponding to typical jet cases are classified. In addition, the influence mechanisms of bubble radial oscillation and the bubble boundary effect on the Kelvin impulse and Bjerknes force of another bubble are explored. The results indicated the following: (1) Three typical double-jet scenarios are discovered, including the newly observed co-flowing jets as well as colliding jets and diverging jets; (2) the Kelvin impulse model accurately forecasts changes in jet intensity and direction—with an increase in phase difference, the jet intensities of both bubbles gradually decrease, then increase inversely, and finally tend to zero; (3) compared to the bubble boundary effect, the bubble oscillation effect is consistently the core factor determining the intensity and direction of the Bjerknes force and the Kelvin impulse for another bubble.