Deflection law in trajectory of large caliber conical-nosed projectile at high-speed oblique water entry

Integrated with high-speed oblique water entry tests of a large caliber conical-nosed projectile and numerical simulations based on the arbitrary Lagrange–Euler fluid–structure interaction method, the deflection behavior of projectile during the high-speed oblique water entry in various conditions is investigated systematically in the present paper. First, the rationality and practicality of related finite element method simulation are verified by the ballistic data in the oblique water entry tests. Then, the force mode and load variation characteristics in the projectile as well as the mechanism for the deflection of trajectory are discussed in detail regarding to the oblique water entry at a high-speed of 500 m/s. Furthermore, the influence of various factors, including impact velocity, oblique angle, and attack angle, on the deflection behavior of projectile is analyzed systematically. It is demonstrated that the instability of projectile motion is mainly due to the pitching moment, which is significantly affected by the actual water entry condition. The impact velocity mainly contributes to the projectile deflection rate, and a higher impact velocity generally results in a more rapid trajectory deflection. The water oblique angle affects both the rate and degree of projectile deflection, and the deflection degree displays different trends in different water oblique angle ranges: when the oblique angle is less than 15°, the projectile usually jumps out of the water, i.e., a yaw phenomenon occurs; when the oblique angle locates in the range of 30°–60°, the deflection trend is almost the same, and the projectile gradually deflects from the initial oblique state to a horizontal state, then to a vertical state, and eventually moves downwards in a “launch” posture with its nose opposite to the entry direction; and when the angle increases to 75°, the projectile can no longer rotate to a vertical state after it rotates to a horizontal state, instead it moves downwards in an oblique state with its nose facing upwards. Comparatively, the attack angle affects the deflection direction, and a positive attack angle usually leads to the increase in deflection degree, while a negative attack angle will change the deflection direction. Related research is of significance in predicting the ballistic evolution characteristics of projectile at high-speed oblique water-entry and optimizing the projectile configuration as well as the impact conditions.