Interaction of cavitation bubbles with a free surface

The motion of single- and two-cavitation bubbles generated by laser beams d irectly beneath a free surface is studied experimentally, using high-speed photography, and theoretically using the highly accurate boundary integral method. Favorable comparisons of bubble shape history and centroid motion a re observed while the numerical calculations provide information on the pre ssure field surrounding the bubbles. A range of responses, including the nu ll impulse state, is obtained for the two bubbles depending on the bubble s ize ratio and the interbubble and bubble-free surface distances, although i n all cases reported in this article, the bubble nearest the free surface y ields a high-speed liquid jet directed away from the free surface. It is al so found that when the free-surface-bubble interaction is strong, a fast fr ee-surface spike is formed for both the single- and two-bubble cases. (C) 2 001 American Institute of Physics.