Experimental Investigation On The Fluid Dynamic Processes Of Water Exit And Water Entry Of A Fast Slender Body

Supercavitation drag reduction technology has had a great impact on the development of naval weapons. Currently, Europe, America, Japan and other developed countries are carrying out basic and applied research on supercavitation drag reduction technology. Particularly, with a focus on the study of the high-speed objects'problems of water exit and water entry, however, as the problems involve two nonlinear free boundaries of the free surface and the cavity surface, featuring strong nonlinear and transient state, both experimental investigation and theoretical numerical simulation need to be further deepened.In this paper, based on our experimental research, changes in natural cavitition of a high-speed slender body from water to the free surface and from the air to the water were observed. This thesis is supported by the Natural Science Foundation of Zhejiang Province under a Priority Project (No. Z1110123). The main work and research results are as follows, (1) According to the experimental needs, water exit and entry test facility of high-speed body that can facilitate the observation was developed independently, (2) The formula as a theoretical basis for calculating the underwater body's velocity in this study was derived by using the measurement data for reducing error. (3) The statistical analysis of experimental data proved that natural vaporization supercavity will appear and the speed of 40m/s is the critical speed of the transition from cavitation into supercavitation when the cavitation number is less than 0.1. (4) The instantaneous velocity of the nail tip just exiting water free surface is the lowest. There is an apparent accelerating trend, but the general trend is still slowing down. (5) With different high-speed photographic equipments, we can observed, if the slender body in the water movement is not vertically upward direction, when the body is moving away from the water, and then get rid of the shackles of gas-liquid, vertical upward movement began. (6) Through observation and analysis of experimental data, the body in the water proved the relationship between time and speed to follow this law, (?), where v0 is the initial velocity. (7) By analyzing the different incident angles of the slender body in the water entry test, a slender high-speed into the water, and after the supercavitation completely formed, the speed of its movement into the water is increased comparing with its beginning moment, reflecting that a supercavity having "drag reduction effect."...