Experimental and theoretical study on the high-speed horizontal water entry behaviors of cylindrical projectiles

In this article, the horizontal water-entry of flat-nose projectiles of two different lengths at impact velocities of 400 m/s-600 m/s is studied experimentally and theoretically. Based on the solution of the Rayleigh-Besant problem, a set of projectile dynamic equations are derived and a cavity model is built to describe the projectile's water entry dynamics. A parameter in the cavity model is determined by employing the principle of energy conservation. The results indicate that the flat-nose projectiles enjoy a good stability of trajectory, the drag coefficient and the velocity decay coefficient are dependent on the cavitation number, and increase along the penetration distance but with a relatively small variation. The maximum cavity radius decreases monotonically with the penetration distance. Projectiles with the same nose shapes at different initial velocities have a basically consistent cavity dimension before the deep pinching off phenomenon occurs. Good agreements are observed between results obtained by the analytical model and the experimental results.