CAVITATION BUBBLE COLLAPSE AND IMPACT IN THE WAKE OF A CIRCULAR CYLINDER

The study for the mechanism of cavitation impulse and erosion has been performed from various kinds of viewpoints. In the present study, a wake-flow field behind a circular cylinder was examined as a representative example of bluff bodies which have a fundamental pattern of separated vortex flow. Cavitation impulses were measured by an accelerometer installed on the outside wall of the test section as well as by the impulsive-force sensor flush-mounted on the inside wall. At the same time, some erosion tests were performed using aluminum plates. Appearances of cavitation bubbles were observed by a stillcamera or a high-speed video camera. According to the result, Karman-vortex-like cavities shed downstream are divided into some parts. Then the cavity positioning near the wall collapses rapidly with a colliding motion towards the channel wall. The frequency of cavitation impulses and the distribution of cavitation-damage pits are investigated together with the appearance of bubble collapse. It is found that the number of damage pits is much smaller than the frequency of passing cavities, even on soft aluminum plate.