Experimental investigations on behaviors of projectile high-speed water entry

Water-entry experiments were conducted in the velocity range 35~160 m/s for the projectiles of the three different geometries including flat nose, truncated-ogival nose and ogival nose. A digital high-speed camera was used to record the detailed processes of water entry and cavity expansion and obtain the hydro-ballistic trajectories and cavity shapes in the early stages of water entry for the projectiles of the three different geometries. And the effects of the nose shapes on the hydro-ballistic stabilities were compared among the projectiles of the three different geometries. Comparisons indicate that the flat nose projectile has good hydro-ballistic stability in the water, the truncated-ogival nose projectile will deflect in the late stage of water entry which is resulted from the deflecting force on the projectile nose, by contrary, the ogival nose projectile will deflect in the early stage of water entry which has the worst stability. By considering the cavitation number was a velocity-dependent factor, a modified mathematical model was proposed to predict the velocity attenuation of cylindrical projectiles and a cavity dimension model was presented based on the energy conservation. The calculations are in good agreement with the experimental results.