Unstable Cavitation Behavior in a Circular-Cylindrical Orifice Flow

The cavitation characteristics were experimentally investigated about long circular-cylindrical orifices of various throat lengths including the orifice with a trip wire. Especially, the shedding process of separated vortex cavity was examined in detail with the observation using high-speed photography. The cavitation impact was measured with an accelerometer. As a result, it is found that the periodic shedding of the cloud-like cavity can be observed characteristically in the transition cavitation stage and is dependent on the formation and coalescence of micro-vortex cavities on the separated shear layer as well as the reentrant motion after the shedding and collapse. It is also pointed out that it forms a feedback loop in the self-exciting mechanism. The estimation determined from two velocity ratios is shown on the Strouhal number of cloud-like cavity. The clear shedding of cloud-like cavity appears near the cavitation impact-peak region and remains almost constant, irrespective of the difference in orifice length. The transition from the throat cavitation to the jet cavitation downstream of the orifice throat can also produce the other impact-peak stage.