Numerical Study of Collapsing Torus Bubble Cloud near a Wall

In the collapse of a single bubble near a wall, the wall surface is eroded by the secondary collapse of the torus bubble cloud. In the present study, direct numerical simulations of the collapse of a torus bubble cloud near a wall surface were performed using a mixture model with the VOF method to investigate the interaction of microjets and shock waves and the effect of shock wave focusing on the bubble collapse pressure. In particular, the effect of the bubble distribution in the torus bubble cloud on the shock wave focusing was examined. Simulations of the collapse of a torus bubble cloud with a non-uniform bubble distribution, in which bubbles are slightly concentrated in one or two locations based on a uniform bubble distribution, show that the bubbles collapse from lower to higher bubble number density regions. The maximum bubble collapse pressure in the case of non-uniform bubble distribution is more than two times higher than in the case of uniform bubble distribution with the same total number of bubbles in the torus bubble cloud due to the focusing of the shock wave.