Cavity, ballistic, and deformation characteristics of high-speed projectile during oblique water-entry at sideslip angles

Initial perturbations substantially undermine the ballistic stability and structural integrity of projectiles during high-speed water entry. In this study, a bidirectional fluid-structure interaction numerical approach was developed, incorporating structural elastoplasticity and fluid multiphase flow models. This approach is simultaneously accounting for stress transmission across different material structure interface boundaries within the projectile solid domain. The validities of the numerical method were established through the high-speed water-entry experiments involving yaw motion and the water-entry experiments with elastic response measurement. Several numerical simulations were conducted to investigate cavity evolution, surface wetting, hydrodynamics, trajectory, and structural deformation characteristics of projectiles at a velocity of 700 m/s, a water-entry angle of 3°, and various sideslip angles of 0°–5°. The results indicated that 4.7°is the critical angle at which the projectile undergoes plastic deformation. This result enables the classification of projectile water-entry behaviour into two categories. For Type I, the sideslip angle induces trajectory deflection; however, the trajectory remains straight or slightly curved, and the cavity shape remains regular. For Type II, the projectile exhibits bending and deformation in terms of cavity formation, trajectory, and structural integrity. From the Type II, the study further indicates that with an increase in the sideslip angle, the wetting on the projectile surface in the positive direction of yaw motion will cause the trajectory bending in both yaw and pitch planes, leading a trend that projectile to ascend above the water surface. Additionally, based on the analysis of the different segmental structural response, which also revealed the ballistic bending and the wetting of the head and tail of the projectile induce plastic bending deformation in the projectile. Ultimately it is discovered that during plastic bending deformation, projectile wetting, forces, motion, and plastic structural strain engage in complex coupled interactions.