Study On The Mechanism Of Near-free Surface Supercavitation

The reason why the supercavitating flow has an important application in the design of weapons such as high speed torpedo,antisubmarine rocket,submarine-launched missiles/projectile in water is that the drag reduction effect can reach 90% when the object moves under water at high speed.However,the collapse of the vacuole can cause damage to the machine,such as the cavitation of water pumps and turbines.Therefore,it is of important practical significance to study the flow mechanism of supercavity in detail.The development of modern ultracavitation weapons has considered the installation of guns at the lower part of the submarine and the carrier’s draft line,aiming to be at a sufficient distance from itself that the launched supercavitation projectile intercepts torpedoes or other weapon,it is necessary to consider the hydrodynamic properties of supercavitation flow in shallow water.In order to study the law of motion of objects near the free surface,this paper uses Fluent software to simulate the fast moving process of objects under different water depths and different velocities,and monitors the formation process of supercavity and the change process of free surface,and calculates wave height and wave location of free surface under different conditions.The study found that within a certain range of numerical simulations the supercavity pulls a tilted pilot wave above the surface of the water,with the leading edge of the wave exceeding the head position of the object or supercavity,because the fast moving object forming supercavitation on the surface squeeze the shallow water layer.In the deep water level,the free surface fluctuations are not too obvious,while in shallow water,the free surface fluctuations.With the increase of water depth,the wave height caused by the free surface fluctuation al-so decreases,while wave-making position of free-surface is farther away from the front of the object.In addition,as the object velocity increases,the wave height induced by the free-surface fluctuation also increases.In addition,the regularity of morphology and size change of supercavitation were also measured at different water depths and different velocities,which were compared with the semi-empirical formulas proposed by the predecessors.Due to the limitation of calculation conditions,this paper focuses on the numerical simulation of two-dimensional supercavitation flow at different water depths and velocities.For the three-dimensional numerical simulation,the results of two-dimensional numerical simulation are supplemented and verified.The simulation results are also compared with the semi-empirical formulas of predecessors.