Fragmentation of cavitation bubble in ultrasound field under small pressure amplitude.

• Cavitation bubble fragmentation was investigated through a three-dimensional simulation and experiment. • The bubble takes a non-spherical shape resulting from the pressure distribution around the bubble. • The non-spherical oscillations of bubble are amplified during its high-frequency oscillations after Rayleigh collapse. • The amplified oscillations cause the bubble fragmentation. 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. [ABSTRACT FROM AUTHOR]