Graduate School of Environmental Studies, Tohoku University, Miyagi 980-8579, Japan.
Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan.
Ultrason Sonochem. 2019 Nov;58:104684. doi: 10.1016/j.ultsonch.2019.104684. Epub 2019 Jul 19.
In the present study, dynamic behavior and fragmentation mechanism of acoustic cavitation bubbles are investigated under relatively small pressure amplitudes of ultrasonic wave through a three-dimensional compressive multiphase flow simulation and experimental observations. It is found that the oscillating bubble takes a non-spherical shape soon after occurring the Rayleigh collapse following the sound pressure distribution around the bubble. Then, the amplitude of non-spherical deformation is enhanced during small high-frequent oscillations after the Rayleigh collapse due to the fluid inertial effect. Finally, the oscillating bubble is fragmented into two smaller ones with the Laplace pressure gradient becoming the final trigger of bubble fragmentation. Besides, the results reveal that the temperature of bubble surface is varied when the non-spherical bubble deformation is large, while during spherical bubble oscillations the surface temperature remains almost unchanged.
在本研究中，通过三维压缩多相流模拟和实验观察，研究了在相对较小的超声波压力幅度下，空化气泡的动力学行为和破碎机制。结果发现，在声压分布周围的瑞利崩溃之后，振动气泡很快呈现出非球形形状。然后，由于流体惯性效应，在瑞利崩溃之后的小高频振动期间，非球形变形的幅度增强。最后，由于拉普拉斯压力梯度的作用，振动气泡破碎成两个较小的气泡。此外，研究结果表明，当非球形气泡变形较大时，气泡表面的温度会发生变化，而在球形气泡振动期间，表面温度几乎保持不变。
