Research Of Cavity Shape And Hydrodynamic Characteristics Of Underwater Kinetic Energy Projectile

Supercavitation technology is a fresh theory and approach for the drag reduction of underwater bodies. Supercavitation flow is one of the most complicated multiphase hydrodynamics, which involves unsteady flow, compressibility, phase transformation, turbulence and other complicated hydrodynamics phenomena, and all of those behavior and properties involve great difficulties for the understanding of the cavity flow. In the content of this dissertation, numerical simulation methodology for vapor-filled and gas-filled cavity shape and drag behavior of kinetic energy projectiles is developed, and a matched laboratory experiments supercavitation kinetic energy projectiles were conducted. The major contributions of the present study are summarized below:The numerical simulation methodology of cavity shape and hydrodynamics characteristics of underwater kinetic energy projectile is conducted. The turbulence models used in supercavitation numerical simulation are analyzed. The numerical results are compared with the experimental results, and the suitable turbulence model is chosen for the future research.Numerical simulation studies on the hydrodynamics characteristics of the natural cavity flow over circular cylinder are conducted. The computation works include the analysis the influence of the aspect ratio on the cavity shape and drag characteristics, the cavitation number on the dimensionless length and diameter of the cavity, the cones, chamfer and flute on the circular cylinder on the cavitaion and drag characteristics. Direct comparisons experiments of circular cylinder kinetic energy projectile are conducted.The cavity shape and hydrodynamics of natural supercavitaion kinetic energy projectile are investigated. The influence of the location of the cavity closure on the pressure drag coefficient, friction drag coefficient and the total drag coefficien are analyzed. Numerical computation study on underwater projectile's outline parameter, including diameter and length of cavitator, the aspect ratio of projectile, tails contour, and surface condition, And get the behavior and properties of cavitaion and drag reduction. The computation works are conducted on the influences of angle of attack of cavitator and angle of attack of projectile on the outline of cavity, drag, and lift behavior, the results show that the angle of attack of bodies induce displacement away from the axis of initial cavity, the angle of attack of cavitator make the lift coefficient increase greatly. The influences of projectile mass, drag coefficients, initial speed, and launch depth are investigated.When the partial natural cavitaion is ventilated, the ventilated supercavitation is obtained. The ventilated supercavitation projectiles are obtained at middle velocity, and the ventilated supercavitation shapes are investigated. The drag coefficients after the forming of supercavitation and the ventilation volume rate that can form supercavitation at different cavitation numbers are obtained. The velocity, velocity attenuation and displacement of projectile at different time obtained. Compaired with the unventilated projectile, the ventilated projectile has slow velocity attenuation, long displacement and small drag coefficient. The drag reduction characteristics of supercavitation are validated.The correlation motion hydrodynamic characteristics of underwater projectile are investigated. Using the numerical simulation the drag behavior of two circular cylinders in tandem arrangement is obtained, and compared with that of one circular cylinder. The force of two circular cylinders is analyzed, and the effect of model parameters on the drag is obtained. The results shows that the drag decreases a lot as two circular cylinders are arranged in tandem. The drag behavior of three circular cylinders in tandem arrangement is investigated, and the supercavitation drag reduction is obtained as multi circular cylinder is arranged in tandem. The bubble motion at tail of underwater projectile is studied, and the effect of bubble motion on launch frequency as multi circular cylinder is arranged in tandem. The hydrodynamic of two circular cylinders parallel arrangement is investigated, and the effect of distance on the drag coefficient of underwater projectile is studied. The side force appears when the distance is small.