Gas entrainment behaviors in the formation and collapse of a ventilated supercavity

• Ventilated supercavitation studies in steady and unsteady flows are conducted.
• Ventilation hysteresis has been examined with respect to formation and collapse.
• Supercavity formation process is governed by the coalescence of individual bubbles.
• Supercavity collapse is determined by the pressure difference inside and outside of cavity.
• Both formation and collapse of supercavity are dependent on the flow unsteadiness.

The present work reports some interesting gas entrainment behaviors in the formation and collapse of a ventilated supercavity under steady and unsteady flow conditions. Our experiments show that the gas entrainment required to establish a supercavity are much greater than the minimum gas entrainment required to sustain it, and these gas entrainment values depend on Froude (Fr) number, cavitator size and the flow unsteadiness. Specifically, the measurements of the formation gas entrainment coefficients under different Fr numbers indicate that it does not monotonically increase with Fr but displays increasing and decreasing trends in different regimes of Fr. On the other hand, the collapse air entrainment coefficient initially decreases with Fr and then approaches to a constant. Similar trends of formation and collapse gas entrainment coefficient are observed for different cavitator sizes. Moreover, the introduction of unsteady gusts causes a slight monotonic increase in the formation and collapse gas entrainment requirements. Our study points out the crucial factors to be considered in the estimation of gas storage requirements for a ventilated supercavitating vehicle.