Probe Into Internal Flow Structures of a Ventilated Supercavity
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This study presents the first systematic experimental investigation of the internal flow structures of a ventilated supercavity using flow visualization and particle image velocimetry (PIV). Experiments are conducted in the high-speed water tunnel at Saint Anthony Falls Laboratory. A backward-facing cavitator mounted on a hydrofoil is used to generate the cavity. Fog particles are introduced into the cavity through the ventilation line, and then illuminated by a laser sheet to visualize the internal flow. A high-speed camera is applied to record internal flow images both for visualization and PIV purposes. The visualization images capture the shape of the supercavity and reveal the patterns of particle movements inside the cavity. The PIV images are processed to obtain the instantaneous and averaged 2D velocity fields. The measurements are performed for the supercavities of two closure modes, i.e. the re-entrant jet (RJ) and the twin-vortex (TV). The flow visualization shows some common features of internal flow across RJ and TV supercavities, including the recirculating flow region near the cavitator, the internal boundary layer extended from the interface as well as the reverse flow in the center portion of the cavity. Furthermore, time-averaged internal velocity field from PIV provides a quantification of streamwise extent of the recirculating flow region, the variation of the thickness of the internal boundary layer along the interface and the magnitude of reverse flow. The analysis of the PIV flow field indicates the TV supercavity yields a longer streamwise extent of the recirculation region, a thinner internal boundary layer and a stronger reverse flow.