The interreaction mechanism between the supercavitation and the free interface of the submarine-launched missiles or projectiles with supercavities has not been clearly understood. And the description about the supercavity shape in an unsteady flow with gravity also needs to be further investigated. An experimental study on underwater high-speed projectiles was carried out in a self-designed experimental facility. The water-exit process of projectiles and the shape change of supercavities were recorded by a high-speed camera. The size
contour
formation and collapse of the supercavities were measured and analyzed. The experiment data were compared with the theoretical formula and semi-empirical formula. The results show that under the studied conditions
the semi-empirical formula of Savchenko can be extended to the cavitation number less than 0.12. In addition
the experimental data are higher than the theoretical value given by Vasin considering the effect of gravity. A coefficient is added to modify the given formula. Furthermore
the experimental study shows that the shape of projectile head has great effect on the size of the formed supercavities. When the supercavities come into contact with the free surface
the supercavity diameter will be increased to a certain extent.
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