Water Entry Flow-Field Visualization of the ObliquePenetration of a High-Speed Projectile

To study the air/water interface deformation and breakup, the water bubble and the blast waves in water, we launched a high-speed projectile using a vertical second-stage gas gun, and visualized the flow-filed close to the air/water interface using the laser shadow and schlieren photography.The images show that the high pressure air downstream the projectile overtakes the projectile at the speed of about 350 m/s and generates blast waves in the air.In the meantime, the blast waves and cavitation bubbles are also generated in the water.The air blast wave reflects on the air/water interface but cannot deform it due to water's large inertia at such a short time.The projectile traveling is not disturbed although the reflected blast wave interacts with it.The droplets cloud from the broken interface is produced after the projectile water entry.It is hard to distinguish the border between the bubbles and the droplets clouds.For projectiles with different head shapes, the bubbles are obtained in different shapes and sizes but the projectile trajectory is seldom disturbed.Similar flow-field characteristics can be identified for a projectile at the speed of 1.8 km/s but with different size and shape of clouds and bubbles.The results demonstrate that such a vertical two-stage gas gun can provide a way for experiments of projectile water entry.