Research On Multiphase Flow And Trajectory Characteristics Of Unsteady Movement Of High Speed Projectile

The supercavitation drag reduction technology is a concerned way of greatly reducing the skin friction drag of the underwater weapon.The supercavitating projectile using the supercavitation drag reduction technology is mainly applied to the anti-torpedo and anti-mine warfare systems.The complex flow phenomena such as passing through free surface,cavitation,turbulence,and tail-slapping will occur when the supercavitating projectiles move underwater or enter water.The characteristics of the complex multiphase flow field which includes air,water vapor and liquid water are key scientific issues in the development of the supercavitating projectiles.Therefore,it is of great theoretical and practical value to investigate the characteristics of multiphase flow field and ballistics of high-speed projectile.In this paper,the multiphase flow field and trajectory characteristics of a high-speed projectile are studied by combining theoretical analysis,numerical simulation and experimental investigation.The main contents and results are as follows:Based on the theory of homogeneous equilibrium flow model,the basic numerical method for calculating the horizontal movement of a high-speed projectile is established.Based on the SST turbulence model and the cavitation mass transport equation,the numerical method for calculating the horizontal movement of a high-speed projectile is established by solving the RANS equation of the mixture of water vapor and liquid water,in addition,the validity of the numerical method is verified by the experimental results.The numerical research of the horizontal movement of a high-speed projectile under different angles of attack and with or without empennages is carried out using the established numerical method.The influences of the angles of attack and with or without empennages on the cavity shapes and the hydrodynamic characteristics of the projectile are obtained.Combined with the mesh deformation method based on the displacement diffusion model and the second development of the CFX software using the CEL language,the rigid body motion equation of the projectile is implanted to the CFX solver code and the numerical method which can calculate the horizontal movement and the tail-slapping movement of the projectile is established.The numerical simulation of the horizontal movement and the tail-slapping movement of the high-speed projectile under different center-of-mass positions and initial perturbed angular velocities is carried out using the established numerical method.The effects of the center-of-mass position and the initial perturbation angular velocity on the unsteady multiphase flow field and tail-slapping movement are obtained.The free flight experiment of high-speed projectile horizontal movement is carried out by using the setup of light-gas gun.The image data of the horizontal movement and tail-slapping movement of the high-speed projectile are obtained by high-speed camera measurement,and the velocity,trajectory and attitude of the projectile are obtained by processing the image data.The evolution of the cavity and the characteristics of the closure and shedding of the cavity are analyzed.In addition,based on the experimental results,the empirical coefficients in the independent expansion principle are modified and the cavity profiles under different depths are studied by using the modified independent expansion principle.The experimental study on the free flight of high-speed projectile entering water obliquely is carried out by using an oblique placed light-gas gun.The characteristics of the multiphase flow field,such as the evolution of the cavitation shapes and the shedding of the vortex during the different period including initial impact,cavitation inception,and cavity closure of the high-speed projectile are analyzed.In addition,the variation laws of trajectory under different headforms and initial water entry velocities are obtained,and the interaction mechanism between projectile trajectory characteristics and multiphase flow field is revealed.