Experimental Study on Interaction of Two Collapsed Cavitation Bubbles
In this study, two cavitation bubbles were generated by rotating a U-tube filled with water. Cavitation bubbles are generated separately in two different L-tubes. One of the cavitation bubbles was then moved to a specific stand-off distance from the other bubble through a connection tube. Adjusting these two bubbles to the desired stand-off distance, a pressure pulse was then triggered to induce the bubble collapse flow. After the bubble collapsed, a liquid zone with low velocity and high pressure was produced. A high speed camera, recording 8000 to 10000 frames per second, was adopted to take the sequential images of the bubble collapse flows in this study. The characteristics of the interaction of the bubble collapse flows were analyzed based on the recorded sequential images. The detailed velocity fields of the interactions of the collapsed bubble flows were measured by particle image velocity (PIV) method. According to PIV measurements, results revealed that the formed liquid zone propagated radially. The movement of the liquid zone not only influences the motion of the flow field, but also produces disturbed flow between the bubbles. After the pressure imposed on the bubbles, the effect of the interaction of the pressure waves between two bubbles led to the disturbed flow field, resulted in the Kelvin-Helmholtz , Richtmyer-Meshkov and Rayleigh-Taylor instabilities. Experimental results showed that the effect of changes in the pressure field on the bubble appearance, thrust and interactions increased as the distance parameter γ value decreased. While the distance parameter γ value was much larger than the radius of the bubble, the bubble collapsing phenomenon would not be affected by the drag of each bubble. The phenomenon was equivalent to the motion process of a single bubble. In addition, the complex phenomena of the collapsing flows of two cavitation bubbles were presented and analyzed clearly.