Water Entry Multiphase Flow Around Double Revolution Body In Parallel

The water entry in parallel refers to a process in which multiple revolution body are arranged in parallel in space and in a certain order from the air through the free liquid surface into the water in a very short time,and which not only has the normal phenomenon such as the water entry cavity,splash on surface of water and re-entrant jet,but also refers to the multiple revolution body affect mutually and the interrelationship between the motion and flow field,that means it is a typical dynamic fluid body interaction problem.The problem of water entry in parallel has a strong engineering application background,for example,the spreading of mines and the water entry of airborne mine clearance supercavitating projectiles,and the water entry process of aerial torpedo and antisubmarine missile.In this paper,the theoretical analysis,experiments and numerical simulation methods are used to study the development of water entry cavity,the evolution of multiphase flow field structure,the motion characteristic and the mechanisation of ballistic instability during the process of double revolution body water entry in parallel under the low Froude number,analyzed the influence factors of the water entry cavity evolution and the ballistic instability,and obtained the critical space-time conditions of ballistic instability.The specific research content and achievements are as follows:Push-pull electromagnets and track brackets are used to design a experimental system that can realize the revolution body water entry at different speeds and different times.The experimental image data is collected by a high-speed camera method,and through the self-programming procedure,the displacement of the centroid and attitude angle of the revolution body batch automatic extraction is achieved.Based on the RANS equation,a numerical simulation method is established,the VOF method and six-degree-of-freedom model are introduced,and then the overlapping grid method was used.Then we verified the validity of the calculation results.Based on the experimental method,the evolution characteristic of cavity and motion during the process of double revolution body water entry in parallel is studied,and the flow characteristics and the evolution of the cavitation during the process of water entry in separate and in parallel were compared and analyzed.The effects of water entry velocity and distance between revolution body axies on the evolution of cavity shape and the closed form were analyzed.Based on the theory of potential flow,and based on the two-dimensional theory of cavity dynamics,the two-dimensional perturbation velocity potentials from the other cavity are analyzed through asymptotic theory,and a three-dimensional nonlinear influence function is introduced,and a three-dimensional cavity dynamic model is established.Based on this model,the three-dimensional evolution of water entry cavity was studied.Base on the numerical method,the characteristic of multiphase flow and body motion are researched.Some Complex flow phenomenon such as the instability of convection film,stagnant strip,open cavity boundary are studied.The ballistic instability mechanism of the revolution body is given,and the influence of the position of the centriod and the relative density on the movement characteristics is discussed.Using a combination of experimental and numerical method,the characteristics of water entry cavity evolution,multi-phase flow field characteristics,and rotational body motion characteristics between the process of water entry in parallel with different water impact time were studied.According to the size of the time difference of water entry and the disturbance intensity,the disturbance is divided into three types of disturbances: strong disturbance,critical disturbance and weak disturbance.Finally,through the statistics of all the experimental and numerical calculation results,the critical space-time conditions of the ballistic instability are studied.