Numerical study on the water-entry of asynchronous parallel projectiles at a high vertical entry speed

Abstract

This study investigates the water-entry characteristics of asynchronous parallel projectiles with vertical entry speeds of 400 m/s for four different water-entry intervals numerically. Experimental studies on the cylinder and the projectile at a high oblique entry speed are carried out to validate the numerical method. The influences of the asynchronous parallel water-entry on flow filed characteristic, trajectory stability and drag reduction performance are conducted in detail. It can be found that the cavity of the first launch projectile is squeezed and the cavity of the following launch projectile expands. Finally, the cavities of two asynchronous parallel projectiles fuse and gradually elongate. For the minimum interval, a tail-slap happens on the first launch projectile, and the following launch projectile loses its trajectory stability totally. For the maximum interval, the following launch projectile is greatly affected by the strong interference of the cavity of the first launch projectile and shows a poor capability of stable. Besides, the water-entry of the first launch projectile decreases the maximum value of the impact load on the following launch projectile obviously. Due to the deformation of the cavity induced by the asynchronous parallel water-entry, the wetting phenomenon occurs on both projectiles, which results in the enlargement of the drag force coefficient and the instability of trajectory.