Experimental Investigation on Shallow-angle Oblique Water-entry of a High-speed Supercavitating Projectile

The shallow-angle oblique water-entry of a high-speed supercavitating projectile is studied by using the high-speed photography technology. The characteristics of the ballistic trajectory, splash formation and underwater pressure wave propagation during the initial water-entry impact at different sideslip angles are observed and analyzed from the underwater pressure signal monitored along the left side of the trajectory. The results show that the small sideslip angle of the projectile has few effect on the smooth cavity formation and the enter trajectory stability during the high-speed oblique water-entry at small entry angle. The larger sideslip angle is able to lead to the severe water atomization in the cavity, the ballistic deflection and the projectile damage. The increase in the sideslip angle can exacerbate this instability. The impacts of the cavitator and the warhead conical section on the free surface at a small entry angle make the splash be an approximate symmetrical "butterfly shape" in birds-eye view. The sideslip angle has inverse influence on the symmetry of the front half of splash comparing with the rear half of splash. Large changes are presented in the splash range with the increase in sideslip angle. The symmetry axis of the front half of splash is deflected with the increase in sideslip angle. The changing process of underwater pressure wave induced by the water-entry impact is divided into two stages: the initial pressure fluctuation stage induced by the initial impact of the projectile on the water and the fluctuation stage of high frequency induced by the superposition of the pressure waves from various directions. The two pressure fluctuation stages show different variation characteristics with the corresponding water entry state due to the increased sideslip angle. © 2020, Editorial Board of Acta Armamentarii. All right reserved.