Interaction of Cavitation Bubbles on Surfaces

Patterned structures on solid surfaces can be used as controlled nucleation sites for cavitation. Etched micro-pits on hydrophobic solid surfaces trap small amounts of gas during immersion in water, which--when lowering the pressure--serve as bubble nucleus. Using specifically patterned surfaces, the dynamics of a few bubbles with controlled distances is investigated. The temporal evolution of the cavitating bubbles is visualized stroboscopically and with high speed imaging. When the inter-bubble distance is sufficiently small, the bubbles merge through a series of fascinating intermediate 3d shapes. Morover, bubbles on the edge of the pattern `shield' the bubbles inside, thus delaying the collapse of the interior bubbles. The results are reproduced with the help of axis-symmetric boundary integral simulations.