Numerical study on the high-speed water entry of projectiles at extremely small angles

This paper investigates the stability mechanisms and influencing factors of high-speed projectile water entry at extremely small angles through numerical simulations. The finite volume method, volume of fluid multiphase flow model, and overset grid technique are employed to simulate the water entry process. An underwater stable projectile is designed, and the ballistic characteristics of projectiles entering water at angles of 1° and 2° are analyzed. The critical entry angle and the primary causes of ricochet are identified. At an angle of 1°, the projectile experiences a whip phenomenon during water entry, causing the cavitator to rotate out of the water surface and revealing an extensive wetted area on the lower surface, ultimately leading to ricochet. According to the primary causes of ricochet, the effects of entry velocity and projectile mass on the critical range of entry angles are explored. The results indicate that at higher entry velocities (200-1200 m/s), changes in entry velocity do not affect the critical entry angle. However, at lower velocities (100 m/s), the unbalanced pressure contributes to improved entry stability, thereby reducing the critical entry angle. Furthermore, increasing the projectile mass can effectively reduce the critical entry angle and improve the ballistic characteristics.