Collapse Pressure of Wall-attached Bubble in a Bubble Cloud

Cavitation erosion is a serious problem in turbomachinery and hydraulic equipment. It is well known that cavitation bubble cloud collapse is the most destructive for material erosion. However, it is not clear which is dominant, the microjets formed by the collapse of bubbles or the focusing of shock waves traveling through the bubble cloud. The interaction of the microjet and the shock wave is also not clarified. In the present study, direct numerical simulations of the collapse of a bubble cloud were performed using a mixture model with the VOF method. Especially, during the final stage of the collapse of the bubble cloud, the collapse of the bubble attached to the wall at a contact angle corresponding to the wettability of the wall surface was focused on. The results show that the macroscopic behavior, such as the time evolution of the total gas volume in the bubble cloud, is independent of the contact state of the wall-attached bubble, but the peak wall pressure due to the bubble collapse depends on the initial bubble shape corresponding to the wall contact angle.