Numerical Investigation on the Regime of Cavitation Shedding and Collapse During the Water-Exit of Submerged Projectile

Cavitation may develop on upward-launched submerged objects approaching sea surface with high speed. In this work, the cavitation shedding and collapse during the water-exit of an axisymmetric projectile is investigated using large eddy simulation (LES). High resolution is guaranteed by carefully fulfilling the requisites of y+<1, Δx+<100, and Δz+<40 to resolve at least 80% of the turbulent kinetic energy. The result indicates that the cavity in growth is always undeveloped as the ambient hydrostatic pressure keeps decreasing. The cavity is pushed by the water surface to shed downward and keep shrinking until its final collapse. The vapor inside cavity during the water-exit process is separated by a layer of water so as not to mix with the air. The front of the re-entrant jet barely catches up with the moving wall, and the cavity is pinched off by the joint effect of the jet front and water surface. It is also found that the angle of attack (AOA) generates inversely inclined liquid-vapor contact lines of the cavity leading edge and cavity closure. The advancing contact lines finally intersect on the pressure side to make the cavity break off, which can cause noticeable pressure impulse on the break-off spot. The pressure feature of the water-exit cavitation evolution is studied with intensively arranged monitor points on the wall, which can sense pressure peaks when the liquid-vapor contact lines sweep over them. The instantaneous high pressure induced by cavitation collapse is resolved.