Design Of A Launch System Of High-speed Underwater Vehicles And Research On The Characteristics Of Supercavitation Flows

The whole process about water exit and water entry of a high-speed solid body is consideredas a classical fluid dynamics problem. This phenomenon is very common in our daily life. Therelevant research results have obtained widespread applications in industry, natural science, anddefense technology. However, since the problem with supersonic bubble involves two nonlinearfree boundaries of the free surface and the cavity surface, which features strong nonlinear andtransient state. Neither experimental investigation nor numerical simulation could exactlydescribes these physical process.This Master thesis has studied the problem on water exit and water entry of high-speedvehicles and the resulting supercavitation through experiments. The Master thesis mainlyincludes seven parts as follow:(1) A convenient and repeatable experimental system for studyingon the whole process about water exit and water entry of high-speed vehicles has beenestablished. Visualization study has been conducted to explore the impact effect betweenvehicle and water surface after water entry and water exit of a high-speed vehicle with ahigh-speed camera;(2) It is found that the phenomenon of tail-slap in water entry displaysimpact oscillation between tail end of the vehicle and the wall of cavity. The direct effect of thiskind of oscillation is the occurrence and development of the "three-dimensional oscillating wakespiral track" which is generated at the rear end of the moving body;（3）The flow field of thetrailing zone of the supercaviataion bubble displays extensive turbulent behaviour. The trailingvortices consisting of air bubbles may shed periodically, and a series of vortices alternativelyshed from the both side of the object. The asymmetry of bubbles on the moving body inducesdisturbance in the flow. Thus, it leads to pulsation of pressure and results in divation of themoving direction;(4) The water entry of high-speed moving body may break off the stability ofthe free water surface. The most direct effect is the formation, development and falldown of thesplash. The geometry, lauch speed, and initial attck angle of the moving body are the importantfactors to influrence the stability of water surface;(5) The velocity of the underwater moving bodies dispalys strong decaying behaviour. The moving of the body under the state ofsupercavitation leads to the reduction of the drag force. Therefore, the decaying of the velocitymay reduced, and the role of drag reduction is confirmed;(6) In the water exit, the collaps ofbubble occurs from the upper to down of the underwater moving body. The extent of bubblecollaps may generate big influence on the motion stability;(7) A short period of acceleration maybe produced on the moment of water exit, and the final tendency is still deceleration. When thewater exit is finished, a mixing flow with air-water is formed in the nearby of the free watersurface, which has a moving tendency from down to upper.This Master thesis has done in-depth studies of dynamical characteristic of the problems onwater exit water entry of high-speed vehicles and the resulting supercavitation, and the work willbe a very solid foundation for further research study.