Study on vortex structure and hydrodynamic characteristics of water-exit projectile with shoulder ventilation

During the vertical motion of a water-exit projectile, the gas stored inside is expelled from the shoulder under the effect of pressure differential, forming a ventilated cavity covering the surface of the projectile. This paper explores the vortex structure characteristics of the surface ventilated cavity through numerical simulation and summarizes its impact on the hydrodynamic characteristics of the water-exit projectile. It was found that the end of the shoulder ventilated cavity presents a periodic vortex shedding form. And the existence of the shoulder ventilated cavity can reduce the vertical resistance of the projectile, improve the vertical movement speed, and play a role in load reduction and drag reduction. Additionally, the lateral displacement of the projectile at the moment of water exit decreases by approximately 45.2%, and the deviation angle reduces by about 55.6%, significantly improving the stabilization of its water exit posture. This indicates that the presence of the shoulder ventilated cavity can effectively enhance the hydrodynamic performance of the projectile.