| The transmedium aircraft has the characteristics of efficient penetration,excellent concealment and long range,and its related technologies have attracted the keen attention of researchers all over the world.Considering the complex and harsh aerodynamic environment of the vehicle in the process of combat,the high temperature occurs on the surface result into complex boiling heat exchange phenomenons during the process of deceleration of the vehicle into the water.This paper introduces the influence of heat into the study of the water entry multiphase flow characteristics of projectiles,and analyzes the influence of the coupling of liquid,gas,steam and heat on the multiphase flow characteristics of the high temperature projectiles under different boiling states.Comparison was made to find the changes of the water enrty multiphase flow characteristics without considering the influence of heat.The study provides basic research support for the study of the water entry process of trans-media vehicles,which has high value in engineering.In this paper,a combination of theoretical analysis,numerical simulation and experimental study is used to investigate the water enrty multiphase flow characteristics of high-temperature projectiles under different boiling states with the trans-media vehicle as the research background.According to the theoretical basis of the impact process during the water entry of projectiles,two-phase flow theory,boiling heat transfer and so on,this paper uses the VOF multiphase flow,the evaporation-condensation model and the laminar flow model in the Ansys Fluent as well as the mesh division method of dynamic computational domain to consider the change process of liquid,vapor,gas and thermal multi-field coupled multiphase flow during the water entry of high temperature projectiles and analyze the change of its related multiphase flow characteristics.The main research contents of this paper are as follows:(1)The experimental study of the water entry process of high-temperature spheres and round-headed projectiles was conducted based on the high-speed camera experimental method.A platform was built for the experiments,and experimental images of high temperature sphere and projectiles entering normal temperature and high temperature water were collected.The effects of the temperature difference between the model and the water,the initial entry velocity,and the model size on the multiphase flow characteristics of the water entry were studied and analyzed to provide data support for the validation of the numerical methods used in the subsequent simulations.(2)The numerical model is established by Ansys Fluent and the simulation calculation was carried out.The construction of the numerical calculation method for the water entry problem of high-temperature spheres is based on the control equations of multiphase flow,in which the VOF multiphase flow model,the evaporation-condensation model as well as the the dynamic computational domain for mesh division are introduced,and,the compressibility of the liquid phase and the complex phase transition are taken into account.Then,the validity of the numerical model is verified by comparing with the experimental research results.(3)The numerical model was used to simulate the process of high-temperature spheres entering the water under multiple conditions.The effects of the temperature difference between the model and the water and the initial entry velocity on the evolution characteristics of the cavity and the hydrodynamic characteristics were studied and analyzed by simulating multiple conditions.Then,the boiling phenomenon is analyzed in conjunction with the boiling heat transfer curve to show the characteristics of drag reduction.(4)Based on the numerical calculation method of water entry for high-temperature spheres,the numerical model for high-temperature round-headed projectiles is established,and its validity is verified.The numerical model is used to carry out the simulation of water entry of high-temperature projectiles to study the effects of the boiling heat transfer state of the projectiles at different temperatures on the evolution characteristics of the cavity,the projectile entry attitudes and stability as well as the hydrodynamic characteristics.It has been found that the boiling phenomenon can change the multiphase flow characteristics of the projectile into the water,and the boiling phenomenon greatly reduces the resistance to the water entry process of the high-temperature projectiles. |
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