Research Of Trajectory Characteristics Of Supersonic-supercavitating Projectiles

The supercavitation technology provides an alternative to reduce the frictional resistance of underwater vehicle and almost all the skull of the vehicles is enveloped in supercavities.Therefore,its sailing drag is largely reduced.Consequently,a high speed is achieved and may exceed the underwater sonic speed.The supercavitating projectiles are designed using this efficient drag reduction technology.The supercavitating projectile is typically launched by the airborne or ship borne cannon.This results in a quick attack to extricate the ship from the underwater threats including torpedoes,mines,frogmen and obstacles.This supercavitating projectile is regarded as an effective means for close-in defense.With the advantages of quick response,powerful lethality,high performance-price ratio and precision strike from air to underwater,supercavitating projectiles have a wide potential application.However,because of the problems of trans-medium and transonic speed underwater,the hydrodynamic,the stability mechanism and the motion characteristic of supercavitating projectiles are completely different from the motion stages of air,water-entry and underwater.This presents challenges to design this trans-medium and transonic supercavitating projectiles.The research of motion feature of supercavitating projectiles in the entire trajectory depends on the deep understanding of the problems in kinetics and kinematics,and is beneficial to improve the relevant theoretical system and to promote the engineering application of this weapon system.In this project,numerical simulation,theoretical analysis and trajectory simulation are employed to investigate the numerical methods,hydrodynamic characteristics,mathematic models and simulation technologies of supersonic supercavitating projectiles in different motion stages.The numerical methods are thoroughly validated by the experimental results from literatures,flow-motion coupled numerical simulation results and level-launched experimental results of full-scale model.The motion characteristic of the entire trajectory is studied by mathematical simulation.The key works are summarized as:(1)The numerical model to simulate underwater supersonic supercavitation flow is established using the moving reference frame method to realize the arbitrary motion and the Tait equation to model the compressibility of the liquid.The model is then validated by emprical and experimental results.The numerical model is further utilized to explore the influence of the fluid compressibility,Mach number,cavitation number on the supercavitation flow regime.The method to predict the shape of supercavitaty of the supercavitating projectiles during super-,trans-,and subsonic underwater sailing is obtained.(2)The method to calculate all the hydrodynamic parameters of supercavitating projectiles during underwater sailing is proposed.The operating conditions including different angle of attack,steady rotation and high frequency vibration are simulated by means of moving computational domain.The positional component,the damping component and the inertial component are all numerically computed.Consequently,the description of hydrodynamic force of supercavitating projectiles during underwater sailing is obtained,which is used for the trajectory simulation.(3)The inherent steady oscillation characteristic of the underwater trajectory is found.The mathematic model including “time-delay” effect of supercavity is established to describe the motion of supercavitating projectiles underwater.The results from this model are consistent with the simulation results of flow-motion coupled method.This demonstrates that the motion of supercavitating projectiles underwater has the characteristic of dynamic oscillation,and the amplitude and wavelength of the oscillating motion is fixed.(4)Apart from the hydrodynamic charaqcteristic during the underwater sailing,the hydrodynamic characteristic,the kinetic model and the motion feature of supercavitating projectiles flying in the air are also investigated.The simulation results show that the motion parameters of the projectile are gradually convergent.Taken the motion states at the end of air trajectory as the initial conditions of the water-entry trajectory,the hydrodynamic characteristic,the kinetic model and the motion feature of supercavitating projectiles during the water-entry process are investigated.The simulation results show that the angle of attack and pitching angular speed change largely during the water-entry process when the initial angle of attack is bigger than 2°.(5)The simulation method of the entire trajectory of supercavitating projectiles is achieved by combining the mathematic model of air trajectory,water-entry trajectory and underwater trajectory in time and space.Its suitability is verified with the result of level-launched experiment of a full-scale model and good agreement is achieved.The research provides the theoretical basis for predicting the trajectory,optimal design and engineering application of supersonic supercavitating projectiles.