Experiment on tail-slapping motion characteristics for oblique water-entry of a projectile

Based on high-speed photography technology, the oblique water-entry experiments of high-speed projectile under multiple conditions are carried out. During the experiment, five experiments were conducted for each condition, and the same phenomenon appeared in the experiment. A self-programing is utilized to capture the image’s pixels and extract the experimental data for the experimental photographs. By analyzing the formation, development, and collapse processes of the oblique water-entry cavity of high-speed projectile, the evolution characteristics of projectile cavitation during tail-slapping are concluded. In addition, by comparing and analyzing the variations of the cavity size, and the velocity and acceleration of projectiles with different initial velocities of the water-entry of the projectile, the influence of the initial velocities of the water-entry of the projectile on cavitation evolution characteristics and water-entry motion traits is summarized. The results show that after the tail-slapping of the projectile, part of the projectile tail penetrates through the original cavity and gets wet, and a new tail-slapping cavity is generated backward from the projectile tail. The tail-slapping cavity fits closely with the original cavity. At the end of the tail-slapping, the location of the tail-slapping cavity under the water is basically unchanged. The tail-slapping cavity is pulled away from the surface of the original cavity of the projectile and collapses, while the original cavity at the same depth accelerates and collapses under the influence of the jet generated by the tail-slapping. With the increase of the initial velocities of the water-entry of the projectile, the size of the tail-slapping cavity and the length of the original gradually increase, and so does the maximum wet area of the tail. With the increase of the number of tail-slapping, the velocity attenuation amplitude and the energy loss of the projectile in each tail-slapping increase, and the capacity of the speed storage of the projectile decreases.