Numerical Study On The Cavitating Multiphase Flows And Motion Characteristics Of A High-speed Water-entry Body

For the high-speed vehicles moving from air to water,they involve multiphase flow of solid,gas and liquid in a very short time.During their process of water-entry,a cavity that can completely envelop the moving body could be formed.Since only the head of the moving body get in contact with water,and the impact generated by the fluid is extremely strong,many moving features such as trajectory and movement posture of the moving body as well as the structure itself are easily affected.Related issues are widely occurred in underwater weapons,seaplanes,ships,ocean platforms,biology and so on,therefore it is necessary to well understand the process of water-entry.In this thesis,numerical simulations are performed for understanding the vertical and oblique water entry process.In the numerical simulation,Reynolds Averaged Navier Stokes(RANS)equations is solved to consider the influence of turbulence.Eulerian multiphase flow with cavitation is included for the moving body implemented by dynamical mesh.The numerical results are validated by the existing experimental results.The vertical water-entry is performed by axisymmetric two-dimensioned simulation while the oblique water-entry is carried out in three dimensions.The influence of the geometry of cavitator,the water-entry speed,and the water-entry angle of moving body on the cavity configuration and flow field.In addition,the instantaneous velocity of the moving body during the vertical water entry process,as well as the variation of the drag coefficient,pressure,overload,and the angle of attack of the moving body are carefully reviewed by the influence of the geometry of the cavitator,the initial velocity and water entry angle of the moving body.Considering the strong overload impact caused by high-speed water entry,the flow control by adding porous media in the front of the moving body are also numerically studied.The influence of porous media porosity and thickness parameters on the water entry ballistic characteristics are obtained based on the numerical results.The conclusion obtained in this thesis can improve the understanding of the motion characteristics of the moving body and the development of cavity for high-speed water-entry.The present work could be served as a reference for studying the ballistic characteristics of the moving body.