Interfacial oscillations and internal flow dynamics of a freely closed ventilated supercavity

An experimental investigation was conducted to examine the interfacial oscillations and internal flow dynamics of freely closed ventilated supercavities. Within the present parameter range, five closure modes were observed: Foam cavity, hybrid foam cavity and transparent cavity, re-entrant jet (RJ), hybrid twin vortex and re-entrant jet, and twin vortex. The cavity closure mode exhibits path dependence, and a stable RJ mode cannot be obtained at fixed ventilation rates and incoming flow velocities. The interfacial oscillations of the cavity propagate downstream with time, and their propagation velocity is primarily governed by the incoming flow. The low-frequency pressure fluctuations inside the cavity (0–50 Hz) are influenced by the incoming flow, whereas the intermediate-frequency fluctuations (50–300 Hz) are self-excited by the cavity. In the high-frequency range (300–3000 Hz), equally spaced energy peaks induced by standing-wave effects are observed. For all test conditions, local energy peaks occur at f = 125 Hz in both the pressure spectra and the cavity interface oscillation spectra. The internal flow can be divided into a ventilation affected region, a shear layer region, and a recirculation region. The axial velocity inside the cavity increases with increasing ventilation rate but decreases with increasing Froude number. Limited and gas exchange between the shear layer and recirculation regions is observed within the measurement range, without abrupt or order-of-magnitude variations.