Water drops and cavitation bubbles in microgravity

We realized an experimental setup to study the dynamics of cavitation bubbles inside spherical water drops produced in microgravity (8th Student Parabolic Flight Campaign, European Space Agency ESA). Water volumes of up to 8 ml (25 mm diameter) were expelled through a specially designed injector tube. The latter contained a porous hydrophilic foam and was particularly coated to ensure a stable and attached water drop. Single cavitation bubbles were then generated by an electrical discharge inside the drop. The growth and collapse of the bubble were recorded using a high-speed visualization system (24’000 frames/s). Thereby, we could study for the first time the cavitation phenomenon in microgravity and observe the interactions between cavity and spherical free surface. In particular, the microjet/counterjet formation was visualized and significant counterjet broadening was found when passing from planar to spherical free surfaces.