Trajectory Characteristics Research And Fluid Dynamic Design On Supercavitating Projectiles

The supercavitation drag reduction technology can change the fluid near the surface of the vehicle from water to gas,thus greatly reducing the navigation resistance.After the application of supercavitation drag reduction technology in the field of artillery,the supercavitation projectile launched by artillery can have the ability of underwater combat,and can hardly damage underwater targets such as mines,torpedoes,UUV and frogman,etc.It will play a revolutionary role in the development of underwater short-range defense combat mode and equipment in the future.Supercavitating projectiles have broad military application because of their excellent cross-medium and underwater combat capabilities.However,there are still technical bottlenecks in the development of supercavitating projectile weapon engineering,such as hydrodynamic configuration design,stable water entry,water trajectory optimization and so on.It is urgent to carry out basic theoretical research in related fields.In this paper,numerical simulation,theoretical analysis and experimental study are combined to study the supercavitation flow around projectiles in transonic navigation,hydrodynamic and ballistic characteristics of supercavitating projectiles in transonic water entry and underwater navigation,and hydrodynamic configuration design method of supercavitation projectiles.The main research work and innovations are as follows:(1)A computational method for compressible natural supercavitation flow field of high-speed projectiles is established.Considering the compressibility of water,the computational efficiency and accuracy of different multiphase flow models,turbulence models and cavitation models in the simulation of transonic natural supercavitation flow field are studied thoroughly and systematically.The cavity profile of the projectile entering water and under water transonic navigation as well as the profile of underwater shock wave obtained by numerical simulation are in good agreement with the experimental results in literature,which verifies the validity of the calculation method.(2)The flow characteristics of supercavitating projectiles in transonic water ertry and underwater transonic navigation are studied.The results show that in the process of high-speed water entry,the velocity and angle of water entry mainly affect the opening size and symmetry of the water-entry cavity,but have little effect on the cavity profile which are120 times the diameter of the cavitator from the head,and the angle of attack mainly affects the symmetry of the water-entry cavity.When navigating at transonic speed in water,the development of supercavitation is affected by compressibility.The density and pressure around the projectile head increase,and the compressional wave in front of the projectile head accumulates to form a bow-shaped detached shock wave.The cavitation number mainly affects the overall length of the cavity,the compressibility mainly affects the size of the cavity around the projectile and the angle of attack mainly affects the positional relationship between projectile and supercavity.These conclusions are new features and laws of supercavitation flow characteristics when considering compressibility.(3)The steady and unsteady hydrodynamic characteristics of entering water and underwater transonic navigation under different conditions are studied,and the effects of different parameters on hydrodynamic characteristics are obtained.The results show that there are critical initial velocity and critical angle of attack in the process of projectile entering water,and there are different critical angle of attack with different velocity of entering water.When the initial velocity and angle of attack are less than the critical value,the peak value of hydrodynamic coefficient reaches the maximum when the steady tail-slap is formed,which is beneficial to reducing drag navigation.When the angle of attack is greater than the critical value,the peak value of hydrodynamic coefficient reaches the maximum at the first wave peak of water entry,and gradually decreases to the peak value of hydrodynamic coefficient at steady tail slap,which is harmful to drag reduction.The above conclusion has not been reported publicly.(4)The trajectory characteristics of supercavitating projectile from air navigation to entering water and underwater navigation are studied and tested.Based on the space motion equations of supercavitating projectiles,the influence of initial parameters such as launch angle,attack angle and pitch angle on air trajectory are studied,and the requirement of obtaining better initial parameters of water entry is put forward.The simulation study of projectile’s entering water and underwater trajectory characteristics are carried out by using 6DOF method.The effects of entering water parameters such as angle,velocity,attack angle and angular velocity on the trajectory characteristics of water entry and underwater navigation are achieved.The simulation results of supercavity profile and velocity curve are validated by using the horizontal water entry trajectory test data.The results show that the calculation method is correct and reasonable,and the calculation accuracy is good.(5)The configuration design method of supercavitating projectile is put forward.Based on spercavitation theory and aerodynamics theory,the design method of supercavitation projectile’s head,main section,tail shape and layout are presented combined with the research results of the previous chapters.By using this method,the configuration of a supercavitating projectile are improved and optimized.Compare the simulation and experimental evaluation of the aerodynamic characteristics,cavity profile,hydrodynamic and ballistic characteristics of the supercavitating projectile before and after the improvement,it is considered that the improved supercavitating projectile has both good air stability and water stability,and the water ballistic performance has been greatly improved,which prove the correctness and reliability of the design method of supercavitating projectile configuration.Research results of this paper provide theoretical basis for trajectory prediction,hydrodynamic layout design and engineering application of transonic supercavitating projectile.