Abstract
We have found that cavitation bubbles are generated when a sphere, which is freely falling from a height of several cm above the bottom, is impacting onto a bottom wall. The cavitation bubbles can be categorized into the following three types: 1) a single disk-like bubble generated at the impacting point, 2) multiple spherical bubbles generated away from the impacting point, and 3) multiple bubbles generated at the surface of the sphere and bottom wall. To clarify the generation mechanism of the cavitation bubbles, the following three kinds of experiments are conducted: (1) the experiment of the single free falling sphere impacting onto the flat buttom plate, (2) the experiment of the single sphere pulling up from the flat bottom plate, and (3) the experiment of impact force acting onto a half sphere fixed to a flat bottom plate. The motion of the sphere has been analyzed by using image processing techniques. The result of the experiments shows that the generation mechanisms of the cavitation bubbles are related to the acceleration of the impacting sphere and the shock pressure generated by the impact of the sphere.
