Study On The Initial Characteristics Of High-speed Water Entry Of Rotary Body

High speed water entry of torpedo or projectile is a multiphase flow(including solid,liquid and gas)problem involving free liquid boundary.During the total process of water entry,the body first slams the water surface,produces a shock wave in water,the load changes dramatically.Then,the body move along with cavity that is generated around the body.The degree of understanding of water entry process is related to the development of maritime weapons such as torpedoes.In this paper,the research object is revolution body ignoring the tail wing,the water entry phenomena are studied from the aspects of body impacting and cavitation formation and evolution utilizing the theoretical and numerical simulation methods.The main topics of this paper are as follow:The drag estimate of revolution body entering water vertically with uniform velocity is carried out by the concept of Fictitious Body Continuation combined with the Modified Logvinovich Model.Compared with the results of experiment at low speed,the drag growth region and peak value are more consistent.While,there is an error between the simulation results and the estimate value at high speed.The compressibility of water is some of the factors causing errors.Numerical simulation method based on Reynolds-averaged Navier-Stokes(RANS)equations is used to study the vertical water entry phenomena of a blunt body with half circle head at high speed.The compressibility of water is considered in simulation.The feasibility and effectiveness of the method are proved comparing with the relevant experimental results.The characteristics of shock wave are studied during the process of water entry,including the interaction between air shock wave and free liquid boundary,formation and propagation of water shock wave.Besides,the pressure coefficient acting on cavitator of body,drag coefficient and velocity of body are obtained to understand further.The effect of vertical water entry with high speed is studied from three aspects of the head type,initial velocity and shape of the projectile bodies.The shape of cavities and dynamics of bodies are main investigated.The shapes of cavity at the same water depth are discussed under different water entry conditions.The drag coefficient and velocity changingas water depth are also showed during the process of high speed water entry.The pressure coefficient changing as dimensionless distance that acts on cavitator is discussed.Based on the numerical simulation of the oblique water entry phenomena of a blunt body with flat head,the cavity formation and evolution,the development of fluid characteristics such as pressure and density,and changing of body dynamics are analyzed emphatically.The influences of entry angle and attack angle on the water entry phenomena is investigated separately.The shapes of cavity,body dynamics and pressure load acting on cavitator at the same water depth are discussed.By calculating and analyzing the high-speed water entry of the projectile,some conclusions about the water entry cavitation and the dynamics of the projectile are obtained,which can provide some references for the structure and shape of the torpedo or projectile.