STUDY ON THE BALLISTIC STABILITY OF HOLOW PROJECTIAL DURING HIGH-SPEED OBLIQUE WATER ENTRY

The hollow projectile is a new type of projectile that features a through-hole structure. It offers advantages such as reduced drag compared to the solid projectiles of the same outer diameter, while still achieving high initial velocity when using the same charge. It exhibits complex hydrodynamic and trajectory characteristics when entering water. A numerical simulation study of the high-speed water entry of the hollow projectiles was carried out based on the Reynolds average Navier-Stokes (RANS) equation, the volume of fluid (VOF) multi-phase flow model, the shear stress transfer (SST)k-ωturbulence model, the Schnerr and Sauer cavity model, the six degrees of freedom (6-DOF) motion simulation method, and the overlapping grid technology. The effects of water entry velocity and angle on the water-entry cavity, cavitation, load and ballistic stability were investigated. Comparing the numerical calculation results with the experimental results, the cavity morphology and the center-of-mass trajectory curves were in good agreement with the experimental results, which verified the feasibility of the numerical simulation method. The results show that the water entry velocities have a greater influence on the size of the cavity and the degree of cavitation in the cavity. The higher the water entry velocity, the larger the cavity, the more obvious the cavitation, the faster the velocity decay of the projectile, the more unstable the trajectory, and the earlier the projectile destabilization. The lower the water entry velocity, the smaller the drag and lift coefficients of the hollow projectile are, and the more stable the motion of the projectile is. The water entry angle has a significant impact on the size of the cavity and the degree of deviation of the projectile. The larger the water entry angle is, the larger the cavity at the moment of the projectile deflection is, the more obvious the cavitation inside the cavity is, the smaller the high-pressure region of the head of the projectile is, the smaller the drag, lift, and moment coefficients are, the smaller the deflection angle of the projectile is at the same time, and the more stable the attitude of the projectile is. The smaller the angle of water entry, the faster the deflection angle of the projectile increases, and the more unstable the motion of the projectile will be.