The dynamics of acoustic cavitation bubbles hold significant importance in ultrasonic cleaning, biomedicine, and chemistry. Utilizing an in-situ normal pressure bubble generation and observation system that was developed, this study examined the translational behavior of micrometer-scale normal pressure bubble pairs with initial radius ratio of 1:1 and 2:1 under ultrasonic field excitation. A velocity-distance curve was proposed to quantify the secondary Bjerknes forces during various interaction stages of the bubbles. The findings revealed that equal-sized bubbles underwent an acceleration phase, a deceleration phase, and a velocity jump phase during attraction in both strong and weak acoustic fields. In contrast, bubbles of unequal sizes, due to different oscillation frequencies, experienced multiple acceleration and deceleration phases, presenting asynchronous behaviors. The study further explored the effects of the initial bubble radius, shape oscillation, and volume oscillations on the attraction speed. Results showed that the velocity of the bubble’s centroid decreased with an increase in the initial radius, while intensified volume oscillations increased the secondary Bjerknes force, thereby increasing the centroid’s velocity. Moreover, strong acoustic fields were more likely to induce severe volume and shape oscillations in bubbles than weak fields. The irregular shape oscillations in twin bubbles resulted in shortened durations of acceleration and deceleration phases, reduced peak velocities of acceleration phase, and diminished acceleration during the velocity jump phase. The research provided some mechanical explanations for acoustic cavitation dynamics and its applications.

中文翻译：

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原位气泡对在超声场中平移行为的实验研究


声空化气泡的动力学在超声清洗、生物医学和化学中具有重要意义。利用开发的原位常压气泡产生和观察系统，本研究检查了初始半径比为 1：1 和 2：1 的微米级常压气泡对在超声场激发下的平移行为。提出了一条速度-距离曲线来量化气泡各个相互作用阶段的次级 Bjerknes 力。研究结果表明，等大小的气泡在强声场和弱声场的吸引过程中都经历了加速阶段、减速阶段和速度跳跃阶段。相比之下，由于振荡频率不同，大小不等的气泡经历了多个加速和减速阶段，呈现异步行为。该研究进一步探讨了初始气泡半径、形状振荡和体积振荡对吸引速度的影响。结果表明，气泡质心的速度随着初始半径的增加而降低，而增强的体积振荡增加了次级 Bjerknes 力，从而增加了质心的速度。此外，与弱场相比，强声场更有可能在气泡中引起严重的体积和形状振荡。双气泡中的不规则形状振荡导致加速和减速阶段的持续时间缩短，加速阶段的峰值速度降低，速度跳跃阶段的加速度降低。该研究为声空化动力学及其应用提供了一些力学解释。