Research On Trajectory And Stability Of Projectile Water Entry At Small Angle And High Speed

Due to the advantages of low navigation resistance and fast speed,the supercavitation projectile can hit the underwater target quickly,so great application value had been excavated.The poor stability and anti-interfere ability of the supercavitating projectiles were arisen due to the supercavitation wrapped around the projectile and the movement state of projectiles cannot be adjusted by the thrust and tail fins during its movement.A large initial disturbance will be produced during the impact process of the projectiles water entry with small angles and high speed,then the instability phenomenon such as ricocheting will easily appeared.In order to analyse the cause of the instability of projectile motion in the process of entering the water with small angle,the ballistic characteristics,load characteristics,and cavitation flow fields of the projectiles water-entry with small angles and underwater movement were investigated systematically in this paper by using numerical simulation and theoretical analysis.The main research contents are as follows:Based on the computational fluid dynamics software FLUENT,the numerical simulation method for vehicle water entry with small angles was established by using VOF multiphase flow model,6-DOF model and dynamic calculation domain technology.Then,focusing on the selected calculation conditions in this paper,the influence of fluid compressibility,mesh density,and other factors on the calculation results were compared and analyzed.So,the effectiveness of the numerical simulation method was verified.The process of the projectiles water entry with small angles and high speed was studied based on the established numerical simulation method.The formation reasons of the initial angular velocity at the instant of the projectiles water entry were analyzed and the trajectory,load,and flow fields characteristics of the projectiles water entry under different water entry angles and head diameters were compared.The results indicate that there are two different motion states in the period of tail slapping due to the difference of wetted area,and the wetness position at the front of the mass center of the projectiles will cause the motion instability after the tail slapping motion.Considering the cavitation memory effect and setting the initial condition based on the numerical simulation results,the process of underwater projectiles motion of the tail slapping were investigated by using theoretical method,and the motion law of supercavitating projectiles tail slapping under initial angular velocity and head diameter were analyzed.The results show that the differences of motion characteristics of the projectiles will be decreased gradually under different initial angular velocities along with the time,however,the differences will be magnified under different head diameters of projectiles.