2 Experimental study on the cavity dynamics in high-speed oblique water-entry

An experimental study of high-speed oblique water-entry of projectiles is conducted using photography technology. A light gas gun is used to accelerate different projectiles into water at different entry velocities and entry angles. Initially, the formation, growth and pinch-off of the cavity are presented. The tail-slap motion, shedding of vortices, splash, up-jet, trajectory deflection and surface closure are also investigated. It is found that the time of surface closure is proportional to the cavitation number and the entry angle. The drag coefficients of the projectile wrapped by cavity are investigated. The results indicate that the drag coefficient is primarily controlled by the nose shape but is independent of the length to diameter ratio of the projectile. The predicting formulas for the cavity profile and the maximum cavity size underwater are established. The prediction shows good agreement with the experimental results.