Experimental And Numerical Study On Hydrodynamic Characteristics In Water Exit Of Slender Body

The supercavitation drag reduction technology has a bright future in military and civilian,in recent years,our country has carried out a large number of researches in supercavitation dragreduction technology, also has made a lot of achievements, but compared with foreign countriesespecially America and Britain, in the cavitation and supercavitation research methods andprogress China has not reached the international advanced level. In the aspect of high speedvehicle exit water dynamics and principle research basically is at the primary stage, theachievement is relatively small, so either numerical or experimental research remains to befurther.The aim of this paper is using the method of experiment and numerical calculation of thehigh speed vehicle exit water, the natural cavitation growth and collapse principle and high speedvehicle to the disturbance of free water surface. The main work includes as follows:（1）.According to the requirement of the researches, we independently design and build safe andreliable high speed vehicle emersed experimental system which use high-speed photographysystem to shoot and observate cavitation phenomenon and different model in different angle ofattack exit water cavitation and flow filed form around slender body. we choose differentmodel and different angle of attack exit water. At the same time, we use software to arrange andanalyze valuable experimental data.（2）. Using commercial software FLUENT to simulated theslender body at different angles and velocity conditions exit water, we compare the resultswith the experimental data. Then get some innovative results as follows:(1) Due to the viscidityof the fluid and the slender wall hit bubble collision, cause the ex-water velocity of slender bodyoscillated to lower.(2)When the slender body breaks the surface of water by the timeconstantly,the viscous resistance between the liquid and the wall surface decreased, the vacuolescome from the surface began to break near the free surface, which makes the added mass and thebuoyancy of slender body to down rapidly. It leads to the ex-water velocity increase rapidly thenkeep on shocking to lower when completely exit of the water.(3) The slender body face emergesto the supercavity by the accretion of the slender body speed gradually,the thin wall cavityproduced supercavitation especially the head and the tail is very easy to cause the partial cavity,also the head of the supercavity closure and collapse is consistent with the empirical model’s cavity closure.(4) In the whole experiment we found that: the sharp head has a less effect on itsown level peak, however, the relatively flat blunt tail’s influence on the free surface peak is big,and always the surface uplift occurred earlier.(5)With the increasing of the vehicle’s speed andits own size,the extrusion and impact to the free surface is very strong, the "splash" phenomenonis more obviously, and the influence on the flow field and range expand at the same time.(6)With the nail outlet the angle of attacking increases, the windward and leeward face of the nail’seffect to free surface is asymmetric, and the windward nail’s liquid peak uplift is steep and theinfluence is smaller, on the contrary,the leeward side’s liquid uplift is gentle and the influence isbigger.(7) By means of the numerical simulation of the navigation body’s length diameter ratio,the water velocity, and the angle of attack on the free water surface, the result is consistentwith the experimental results of large disturbance.