CAVITY SEPARATIONS AND ASSOCIATED IMPULSIVE PRESSURES AROUND A CAVITATING CIRCULAR CYLINDER (1ST REPORT, VORTEX CAVITATION IN THE WAKE AND ATTACHED CAVITATION)

The flow pattern and the fluctuating pressures around a cavitating circular cylinder are systematically studied, especially about the wake and the attached cavity separation in the supercritical region of 4x105 < Re < 7x105 in a closed type cavitation tunnel, by means of highspeed photography and time series analyses. The impulsive pressure of about -70kPa in amplitude and of 4ms in half width duration originate within the core of the vortex cavitation, which occurs frequently in the turbulent wake. The attached cavitation is intermittently resulted by the alternate fluctuating pressures from the Karman vortices and its inception point locates within the turbulent transition region where the fluctuating pressures of a bout 7kHz are predominant. In the attached cavitation, the Brennan waves expectedly appear at the boundary between the clear and the cloud cavity, from which a lump of bubbles separate, leaving the clear cavity.