Experimental Research on the Influences of Head Shape and Surface Properties on the Water Entry Cavity

Addressing the problem of the influence of surface properties on the cavity in the process of a moving body entering water, especially the problems of water entry speed and the cavitation evolution of the round-head, air-delivered projectile that has many practical applications, a self-designed launch platform and high-speed camera were used, and the MK46 was used as a prototype to conduct scaled model experiments with different head form types and different surface properties. This paper describes the general process of the moving body entering the water and the generation of the cavity. The relationship between the re-injection flow, the local cavity number and the cavity stability is discussed. At the same time, the effects of head shape, launch velocity and surface wettability on the cavity evolution and motion characteristics were analyzed, including 0 degrees, 57 degrees, 70 degrees, 90 degrees and 180 degrees hemispherical angle-head projectiles with speeds of 2.2 m/s and 3.95 m/s, so as to observe the cavity development and ballistics. The results show that hydrophobic surfaces are more prone to cavities when entering water vertically at low speeds. The influencing factors of water entry ballistics are often the combined effects of head shape, water entry speed and water entry angle. The speed of the hydrophilic surface models with head hemisphere angles of 57 degrees and 70 degrees entering the water is the fastest. This provides a reference for us to design the shape of the projectile. The internal relationship between the cavity shape and the ballistic characteristics is based on the premise that the cavity will complicate the force on the model. The cavity affects the ballistic characteristics of the model by affecting the forces on the model.