Interaction of a cavitation bubble with a spherical free surface

The dynamic of a cavitation bubble inside a water drop is investigated in microgravity in order to analyze the interaction between the collapsing bubble and a quasispherical free surface. Tests are carried in the frame of the 42nd parabolic flight campaign organized by the European Space Agency (ESA). High-speed visualization revealed a significant influence of isolated, finite liquid volumes and spherical free surfaces on the bubble growth and collapse In particular; collapsing bubbles eject two liquid jets escaping from the drop in antipodal directions. The bubble lifetime is significantly shortened in good accordance with a herein derived analog of the Rayleigh- Plesset equation for bubbles in water drops. The spherical free surface leads to a broader counter jet than previously studied for flat free surfaces. The shock waves generated at the bubble collapse are spatially confined, which leads to the formation of a large number of transient micro bubbles. This phenomenon is hardly visible in the ground based experiments when bubbles are collapsing near a flat free surface within a large liquid volume.