Investigation of Internal Flow Velocity Distribution and Gas Loss of High-Speed Supercavitating Flows

Abstract

Internal velocity distribution is an important content of flow structure and reveals the gas loss mechanism for supercavitating flows. Considering the three-phase momentum interactions and the water-vapor mass transport, the water-gas-vapor multi-fluid model is established to simulate ventilated supercavitating flows at high speed in the frame of the nonhomogeneous multiphase flows theory. Based on the model, the gas velocity field inside supercavity is studied. In the case of supercavitating flows around disk cavitator, two vortex cores are formed in the longitudinal plane under the actions of the adverse pressure gradient in the tail and the viscous friction on cavity surface, and are symmetrically distributed about the longitudinal axis. Most inner regions in the cavity cross section are occupied by circulation flows, where the velocity is in the opposite direction of incoming flows and decreases in the radial direction. When passing the vortex center, the velocity changes direction and increases in the radial direction. Part of gas departs to wake flows from the outermost regions close to the section boundary. The results confirm Spurk’s assumption for gas entrainment in detail. It is also found that the gas velocity distribution in the cross section through vortex cores does not depend on cavitation number. Supercavitating vehicle has the similar internal velocity distribution and gas loss mechanism. Due to the added viscous effect of the enveloped body, there are multiple axisymmetrical distributed vortices inside the cavity. The relative distance between the vortex core and the cavity wall increases downstream. Computations of ventilated supercavitating flows at different Reynolds numbers show that the gas leakage is decreasing with increasing Reynolds number for a given cavitation number. This study deepens the understanding of gas loss for ventilated supercavity at high speed, and lays a foundation for further refinement of the dynamic model of the maneuvering ventilated supercavity and the control of ventilated supercavitating flows.

Re-entrant Gas Flows of High-speed Ventilated Supercavity

“…Since ventilated supercavitation was discovered, researchers have made endeavours in this area and some achievements in the formation, hydrodynamics and stability of supercavity [1][2][3][4][5] , but inner flow structures remain little focused. Unlike natural case, where vapor-water mixture interacts [6] , there are gas vortex ring structures inside ventilated supercavity [7,8] . It is inextricably linked with gas loss [9,10] , which not only determines supercavity tail closure [11] , but also is crucial to the flow stability and control [12,13] .…”

“…However, some unsteady factors or processes can induce natural cavitation in high-speed states. Further considering the vapor-water mass transport, the gas-vapor-water multi-fluid model was developed in our recent work [8] and is applied here. In the model, governing equations consist of the continuity and momentum equations of each phase and the volume conservation and pressure constraint equations.…”