Bubbles oscillating in the presence of ultrasound is commonly employed in biomedical applications for drug delivery, ultrasound enhanced thrombolysis, and the transport and manipulation of cells. This is possible because bubbles tend to interact with the ultrasound to undergo periodic shape changes known as shape-mode oscillation, concomitant with the generation of liquid agitation or streaming. This phenomenon is examined both experimentally and theoretically on a single bubble at a frequency of (45 1) kHz. Effects of ultrasonic frequency and power on the flowfield were explored. Experiments revealed different trends in the development of liquid streaming velocities at different acoustic forcing conditions (5.53, 6.80 and 7.02 Vpp), with lowest (0.5 mm/s) and highest (1.1 mm/s) values of time-averaged mean streaming velocity occurring at 6.80 Vpp and 7.02 Vpp, respectively. Simulations captured the simultaneous evolution of bubble-shapes that helped create flow vortices in the liquid surrounding the bubble. These vortices collectively responsible in generating signature patterns in the liquid for a dominant shape-mode of the bubble, and could also generate localised shear stresses for practical application. The velocity and pressure profiles in the liquid around the bubble confirmed the connection of the applied and reflected soundwaves in driving this phenomenon.

中文翻译：

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用于生物应用的低频超声气泡振荡

在超声波存在下振荡的气泡通常用于生物医学应用中，用于药物输送、超声波增强溶栓以及细胞的运输和操作。这是可能的，因为气泡往往与超声波相互作用，经历周期性的形状变化，称为形状模式振荡，同时产生液体搅拌或流动。这种现象在频率为 (45 1) kHz 的单个气泡上进行了实验和理论上的检验。探讨了超声频率和功率对流场的影响。实验揭示了不同声学强迫条件（5.53、6.80和7.02 Vpp）下液体流动速度发展的不同趋势，时间平均平均流动速度出现最低（0.5 mm/s）和最高（1.1 mm/s）值分别为 6.80 Vpp 和 7.02 Vpp。模拟捕获了气泡形状的同时演变，这有助于在气泡周围的液体中产生流动涡流。这些涡流共同负责在液体中生成气泡的主要形状模式的特征图案，并且还可以生成实际应用中的局部剪切应力。气泡周围液体的速度和压力分布证实了所施加的声波和反射的声波在驱动这种现象中的联系。