Ventilated cloud cavitating flow around a blunt body close to the free surface

Ventilated cavitation occurs as a complicated problem if the free surface is close to the cavity boundary around a high-speed underwater vehicle. The present study investigate the cavitating flow around a blunt axisymmetric body very near the free surface. A typical experiment is conducted by using a launching system with a split Hopkinson pressure bar device, and a numerical scheme is established based on large eddy simulation and volume-of-fluid methods. Unsteady behavior, including air entrainment and shedding of the cloud cavity, is observed, and high consistency is achieved between numerical and experimental results. Distinctions of evolution features between the cavities on the upper and lower sides are presented and analyzed. First, strong entrainment of noncondensable air occurs and changes the fluid property inside the cavity, which makes the cavity larger. Moreover, given the small distance between the vehicle and the free surface, the re-entrant jet generated in the upper part is thin and cannot completely cut off the main cavity, which causes the upper part of the cavity to remain approximately unchanged after the growth stage without the occurrence of the shedding phenomenon. Finally, the evolution of vortex structures is also discussed by comparisons with the motions of the air entrainment, re-entrant jet, and shedding cavity.