Research On Water Entry Trajectory And Hydrodynamic Characteristics Of High-Speed Projectiles

The water entry process of high-speed projectile includes many complicated flow phenomena such as phase transition,strong turbulence,multiphase,passing through the free liquid surface.It has the characteristics of nonlinear,unsteady situation,high load and so on.In the water entry process,the cavity shape,trajectory characteristics and hydrodynamic characteristics are affected by many factors.In this thesis,the water entry process of a high-speed projectiles is taken as the research background,and a high-speed projectile with a 5.8mm caliber is taken as the research object,and the computational fluid dynamics software FLUENT 19.0 and MATLAB are used as the tools.The change rules of cavitation shape,trajectory characteristics and hydrodynamic characteristics of high-speed projectile during water entry process is studied by means of theoretical analysis,numerical simulation and experimental research.The main research contents of this thesis are as follows:(1)By analyzing the phenomenon of high-speed projectiles entering water,based on the 5.8mm caliber projectile model,different coordinate systems and motion parameters are defined to describe the projectile motion and force.In the process of high-speed projectile into the water,the force condition of projectiles is analyzed,which lays the foundation for the later analysis of projectile motion and force.(2)Based on Reynolds time averaged Navier-Stokes equations,SST k-ω Turbulence model,VOF multiphase flow model and cavitation model are applied.Combined with 6DOF dynamic grid technology and embedded user-defined programming,the numerical simulation method of two-dimensional model and three-dimensional model of projectile is improved.Comparing the results of numerical simulation with the results of theoretical calculation and experimental,it is found that the trend of the curve is consistent and the error is small,which verifies the accuracy and effectiveness of the numerical calculation method in this thesis.(3)Combined with the dynamic computing domain technology,the numerical simulation of high-speed projectiles vertical water entry process is carried out.The cavitation shape,trajectory characteristics,drag force characteristics,pressure field and velocity field are studied.The influence of the velocity and projectile density on the cavitation flow field in the process of water entry is analyzed by changing the value of other parameters.(4)The three-dimensional numerical simulation of high-speed projectiles in water is carried out by using overlapping grid and 6DOF technology.The influence of different water entry angles on the development of water entry cavity shape,projectile trajectory,velocity,pitch angle,yaw angle,roll angle,drag force,lift force,side force,rolling moment,yawing moment and pitching moment is analyzed.The results show that the shape of projectiles has a great influence on the trajectory stability of projectiles.The conical-flat head projectile is the most stable,followed by the oval-flat head projectile,and the conical-cone head projectile is the worst.The research results in this thesis can provide a theoretical basis for the shape design and engineering application of supercavitation projectile and other weapons,so it has a certain application value for the study of trajectory and hydrodynamic characteristics of high-speed projectile in the process of water entry.