Numerical Study of High-Speed Vertical Water Entry of Hollow Projectiles with Different Aperture Sizes and Velocities

The hollow projectile is a new type of projectile that has complex water entry hydrodynamics characteristics and has attracted significant attention in recent years. As such, it is important to investigate the effects of different entry velocities and aperture diameters on the cavity morphology, cavitation, dynamics, and motion characteristics of hollow projectiles when entering water at high speeds. In this study, four stages of an open cavity, cavity stretching, cavity closure, and cavity contraction in the water entry processes of a hollow projectile at 50–200 m/s and four aperture diameter projectiles at 100 m/s were studied using the volume of fluid (VOF), realizable k-ε turbulence, and Schnerr-Sauer cavitation model. With an increase in the speed, the depth of the cavity closure increases, thereby advancing the closure time. The timing of the surface closure at 50 m/s is clearly different from that at 100–200 m/s. Cavitation is not obvious and is near the cavity wall at 50 m/s, although the entire cavity is almost filled with vapor at 100–200 m/s. The friction resistance has two step points when impacting the water surface and entering the water completely. As the velocity increases or the aperture ratio reduces, the splash is higher, the cavity volume is larger, the cavitation phenomenon is more obvious, the cavity closure time is delayed, and the frictional resistance of the projectile is greater. The results of this study can guide the production and application of hollow projectiles in the future.