Study On The Characteristics Of Flow Field And Impact Load At The Initial Stage Of Projectile Entering Water

The process of transmediate projectile entering water from air across the water air interface is called water entry process,which involves the coupling action and unsteady motion process among air,water and projectile.When the projectile hits the water surface,it will produce a huge impact load.The peak load first increases,and then gradually decreases and tends to be stable with the increase of the projectile’s depth into the water.At the same time,the cavitation shape evolves unsteady during the projectile’s entry into the water.In this paper,the numerical method is used to simulate the projectile entering the water,and the initial characteristics of the projectile entering the water are deeply analyzed.Firstly,the numerical simulation method of projectile entering water is established by using overlapping grid technology and Navier Stokes equation based on Reynolds average.Select realizable K-ε For turbulence model and multiphase flow model,VOF model is selected.Considering the cavitation phenomenon in the process of projectile entering water,schnerr and Sauer cavitation model is introduced.The simulation results are compared with the experimental data in the literature to verify the availability of the numerical model in this paper.Based on the simulation calculation at the initial stage of hemispherical warhead entering the water,the independence between the grid density and the size of the calculation domain is verified.Secondly,the initial water entry process of different warheads under different initial water entry velocity is studied.The flow field parameters,velocity variation,water entry cavitation and impact load characteristics of the projectile are analyzed.The research shows that when the projectile reaches the same water entry depth at the same initial velocity,the cavitation size of the flat head projectile is the largest,the round head projectile is the second,and the sharp cone projectile is the smallest.When the projectile enters the water at different initial velocities,the peak value of impact load increases with the increase of water entry velocity,and the drag coefficient of the projectile has nothing to do with the initial water entry velocity of the projectile.Finally,the influence of different parameters of the rectifier cone in front of the missile on the initial characteristics of water entry is studied,and the evolution law of cavitation formation and collapse is obtained.With the increase of the length diameter ratio of the front rectifier cone,the larger the size of the small cavitation generated by the front rectifier cone entering the water,the more prone the morphological evolution of the large cavitation of the main projectile entering the water to deformation.The single impact load peak can be divided into secondary impact load peak by the pre rectifier cone of the projectile.The rectifier cone with different length diameter ratio can effectively reduce the impact load peak by increasing the impact time of the projectile.Under given conditions,the load reduction rate can reach at least 30%compared with the single half ball head projectile...