Experimental study of bubble cavity effect on ballistic characteristics of vehicle entering water

Abstract

The water-entry process of a vehicle is a typical fluid–structure interaction problem. When the vehicle enters the water at a certain angle, asymmetric loads caused by the asymmetric wetted part can significantly affect its ballistic characteristics and increase the risk of instability. A bubble cavity near free surface can reconstruct the wave surface condition, which makes the vehicle enter the water at a larger angle. This paper experimentally investigates the bubble-cavity effect on the stability of the vehicle during its water-entry process. The results show that the existence of the cavity can effectively improve the stability of underwater motion trajectory of the vehicle, with the angular deviation decreased by 85.7% compared with that in the calm water. In addition, it is found that the existence of the bubble cavity significantly increases the closure speed of the cavitation bubble at the tail of the vehicle after water entry.