On the Collapsing Behavior of Cavitation Bubble Clusters

The appearance of cavitation bubbles near the bubble collapsing stage was investigated on the foil section with a high-speed video camera that was triggered by the signal of impulsive force sensor. The impulsive force always occurred with the collapse of cloud cavity, and in most cases the impulsive force peak was observed several frames (95 μsec. in average) before the cloud cavity appeared to be minimum in its volume. To explain this phenomenon, the shock wave propagation in the bubble cluster into its center was discussed. The authors also simulated the behavior of bubbles numerically. Spherical bubble motion and mutual interference with other bubbles were considered. The results showed that the central bubble near the wall collapsed later than the surrounding bubbles and produced the highest pressure. At that moment the surrounding bubbles had been rebounding and were in growing stage. The results correspond qualitatively to the experimental results.