Investigation Of Multiphase Flow Characteristics Induced By Water Entry Of High-speed Projectiles

The cavity flow during the water entry of high-speed projectile is extremely complicated, which involves turbulence and phase transformation phenomena, characterized by strong instantaneous, nonlinear behavior and high-load situation. The environmental factors of the flow area and structural parameters of the projectile also have major influence on the cavitation development and fluid dynamics. This thesis discusses the trajectory characteristics, cavitation development and fluid dynamics during the vertical water entry of cone-cylinder projectiles, by using theretical, experimental and numerical methods jointly. The main topics of this thesis are as follows:Experimental study on low-speed water entry of spheres is invedtigated to find out the process of the induced cavity and the phenomenon of cavity flow, each stages of the water entry process are classified and difined, which can be regarded as the foundation for later studies on high-speed water entry problems.Theretical method based on Energy Conservation Law and numerical simulation based on RANS(Reynolds-averaged Navier-Stokes equations) equations are used separately to investigate into the cavitating flow induced by the high-speed water entry of the projectiles for a specific problem. The cavity development and trajectory process are studied by using both the methods, good agreement are obtained by using the two methods, the surface closure and deep closure of the avity as well as the cavitating effects are also investigated during the high-speed water entry. Besides, the pressure and velocity distribution of the multiphase flow and the pressure loads acted on the head of the projectile are obtained by numerical simulation.The effects of the flow area factors which act on the cavity development and multiphase flow characters induced by high-speed water entry of the projectiles, such as the operating pressure and density of the gas, are investigated by numerical simulation. The cavity size and development as well as the process of trajectory affected by those factors are discussed, the variation of the cavitating phenomenan inside the cavity is also studied. Finally, the pressure and velocity distribution of the multiphase flow, especially inside the cavity and on the cavity wall, are discussed.The radius of the water entry cavity at the level of the free surface is very important since it will affect the surface closure considerably. Theoretical method is used to decide the change of the radius of the cavity, results based on variable cone-heads and densities of the projectile obtained by numerical simulation show good agreement with the theoretical results. The influences of structural paraments including heads, density, lenth of afterbody and diameters of the projectiles are simulated, the variation of the cavity developments as well as the fluid dynamics are given. Besides, the pressure load that acts on the heads of the projectiles is also discussed for variable structural parameters.