Abstract: In order to study the evolutions and motion characteristics of cavitations in the process of water entry in tandem, the high-speed camera and time release system are used in testing the low-speed tandem water entry of rotary bodies at different initial spacing. The motion characteristics of rotary bodies are identified and extracted using image processing technology, and the influence of the initial spacing of water entry on cavitation evolution, longitudinal displacement and deflection angle of rotary body was obtained through test. The test results show that the cavitation structures and sizes of two rotary bodies are affected during the water entry in tandem at the small initial spacing. With the increase in the initial spacing of water entry, four motion modes, including colliding disturbance, closed cavity disturbance, transition disturbance and weak disturbance, arise in the process of tandem water entry of rotary bodies. In different motion modes, the vacuolizations and motion characteristics of two rotary bodies are quite different. The colliding disturbance mode has the greatest influence on the motion characteristics of rotary body. Key

Key words: twomotionbodies, low-speedwaterentry, cavitationevolution, motionfeature