LAUSR

Abstract This paper describes numerical simulations of the series and parallel water entry of supersonic projectiles with different head shapes, entry velocities, interval times, and interval distances. We focus on the cavity geometry and the drag force characteristics of the projectiles. For projectiles entering the water in series, no cavity is formed by the second projectile. This second projectile impacts and penetrates the water jet, and moves inside the cavity formed by the first projectile. Moreover, the impact drag force coefficient of the second projectile is significantly smaller than that of a single projectile entering the water with the same entry conditions. The cavitation drag force coefficient of the second projectile fluctuates. In the case of projectiles entering the water in parallel, the impact drag force coefficient is slightly smaller than that of single-projectile water entry. After the projectiles impact the water, the drag force coefficient declines sharply, increases again to form a small peak, and then reduces to an approximately constant value that is slightly larger than that of a single projectile entering the water. Additionally, although the outside boundary of the parallel water entry cavity shows a similar shape to that of single-projectile water entry, the blockage effect causes the inside boundary to form an approximately straight line.