Influence Rule of Projectile Density on the Characteristics of High-Speed Water-Entry Cavity

There has been much recent research on high-speed projectiles entering water, but research on the selection of the material for supercavitating projectiles is limited. Some important properties of such projectiles—mass and moment of inertia, for example—are related to the material density, so the projectile’s density has an important effect on the performance of the supercavitating projectile. This study, using Ansys fluent 19.0 simulation software, studied the details of water entry of four high-speed projectiles of the same shape but made of different materials: aluminum (2.7 g/cm3), steel (7.85 g/cm3), brass (8.5 g/cm3), and tungsten alloy (17.5 g/cm3). The cavity shape, ballistic and hydrodynamic characteristics, and cavity flow field characteristics of projectiles with different densities were analyzed for a water-entry velocity of 600 m/s. The results show that within 3 ms, the velocity of a projectile with a density of 2.7 g/cm3 drops to 171.8 m/s, and the velocity of a projectile with a density of 17.5 g/cm3 drops to 433.1 m/s. Increasing the density of the projectile evidently reduces the deceleration of the projectile. The drag coefficient depends, primarily on the size and shape of the projectile, only slightly on its density. Just after water-entry time, the higher the density of the projectile, the faster the expansion of its cavity wall. As time after water entry increases, the expansion velocity of the cavity wall gradually decreases. The simulation results show that the projectile head experiences the greatest pressure, producing a sharp peak, at the moment when it touches the water surface. During the flow stabilization phase, the lower the density of the projectile, the lower the pressure on the head of the projectile. The results of this study will help to guide the selection of material for supercavitating projectiles.