MECHANISM AND CONTROL OF CLOUD CAVITATION

Generation mechanism of cloud cavitation on a hydrofoil section was in vestigated in a sequence of experiments through observation of cloud c avitation by high-speed video and high-speed photo as well as pressure measurements by pressure pick-ups and a hydrophone. The mechanism was also investigated by controlling cloud cavitation with an obstacle fi tted on the foil surface. From the results of these experiments, it wa s found that the collapse of a sheet cavity is triggered by a re-entra nt jet rushing from the trailing edge to the leading edge of the sheet cavity, and consequently, the sheet cavity is shed in the vicinity of its leading edge and thrown downstream as a cluster of bubbles called cloud cavity. In other words, the re-entrant jet gives rise to cloud cavitation. Moreover, cloud cavitation could be controlled effectively by a small obstacle placed on the foil. It resulted in reduction of f oil drag and cavitation noise.