Bubble translation driven by pulsation in a double-bubble system

The pulsation and translation of two cavitation bubbles are studied numerically in sound field. The results show that bubbles' pulsation driven by the sound makes them translate. Different pulsations lead to different translations. Two bubbles will be mutually attractive to each other if they pulsate in phase, while they will be repulsive if out of phase. Furthermore,the secondary Bjerknes force for small phase difference is attractive, and it becomes repulsive for other phase differences up to π phase difference due to the nonlinear effect, although the attractive strength between two bubbles is much larger than the repulsive strength. Finally, one bubble pulsation and the other bubble stationary make the bubbles repel each other.     

Uniform Acoustic Cavitation of Liquid in a Disk

A dynamical propagation model coupled to the oscillation of cavitation bubbles is applied to describe the imploding acoustic field in a cavitating liquid where the acoustic waves transmit from the outside to the inside of a circle disk. Numerical simulation shows that the imploding ability of a ring source can elevate the sound pressure or partly eliminate the decay due to both the bulk attenuation and the attenuation caused by cavitation. However,the imploding ability is limited and there exists a critical radius. When the radius of the disk is larger than the critical one, the imploding ability is not enough to eliminate the attenuation. Fortunately, the cavitation region can be effectively expanded if a hot plate is attached under the center of the disk because the cavitation threshold is related to the temperature of the liquid, which means that a region with good uniformity of cavitation can be enhanced by adjusting the temperature difference between the central and side liquid.