Numerical investigation on the trajectory stability by asymmetric shape effects for water-entry projectiles

The trajectory stability of projectile entering water has obvious influence on its safe entry into water. To make the projectile maintain the initial attitude angle, the influence of different asymmetric shapes on the motion of the projectile is explored. The asymmetric shape refers to the degree of downward deflection of the projectile head tip. A three-dimensional model, combined with the unsteady Reynolds-averaged Navier–Stokes equation and the shear stress transport k-ω turbulence model, is applied to numerically simulate the water-entry motion. The trajectories, the wake vortices, the backside vortices, and the pressure distributions of the nose shape are plotted. The results show that the projectile has a stable trajectory after water entry when the asymmetric ratio is 25%. Compared with the symmetric shape, the attitude angle deflection of the asymmetric ratio 25% is reduced by 89.97%. The cavity volume of the asymmetric ratio 25% is significantly smaller than the others, which results in a smaller swing of the projectile in the cavity and therefore easier to maintain the trajectory. It is worth noting that during stable projectile motion, the hairpin vortex is not prominently observed. However, when the attitude angle varies, the projectile tail induces a vertical force on the wake vortex, causing the emergence of a hairpin vortex.