Study On Multiphase Flow Characteristics In Near-watersurface Skipping Motion Of Disk

Research on trans-media motion is a hot issue in weapon development.As a typical trans-media motion type,near-water-surface skipping motion is widely used in military engineering and aerospace engineering fields,such as near-surface transmedia weapons,detector return and forced landing of seaplane.Near-water-surface skipping motion is the multi-degree of freedom motion that the moving body detaches from the free water surface under hydrodynamics action after it impacts the water surface with a certain speed and inclined angle.It is a complex multiphase flow problem involving transient medium mutation and complex motion response,as well as coupling between solid,liquid and gas.Compared with the multiphase flow characteristics of traditional structure water entry,the cavity evolution,flow field structure,hydrodynamic characteristics and the motion characteristics of the moving body in near-water-surface skipping motion have fundamentally changed.Taking the disk as the research object,an in-depth study on the multiphase flow characteristics in near-water-surface skipping motion is carried out by using the experimental,theoretical and numerical methods in this study.In order to ensure the attitude stability of the disk during the motion process,the disk always has a certain initial spinning velocity,which makes the motion characteristics of the disk and flow field structure more complex.Therefore,this research has high engineering value and theoretical significance.The main research contents and results are as follows:Based on the high-speed camera technology,the experimental research on the nearwater-surface skipping motion of non-spinning disk is carried out.The cavity evolution under different initial motion conditions is studied,and the deformation state of the cavity wall and two typical cavity types are obtained.It is found that the smaller initial inclined angle is more favorable for the disk to detach from the water.Based on the numerical simulation,the influence of the impact angle on the hydrodynamics and motion characteristics of the disk is studied,and the influence law is obtained.Comprehensively considering the water entry impact force and sliding water force acting on the disk by water media in the process of water contact,a dynamic model of near-water-surface skipping motion of disk with a constant inclined angle is established,and the usability of the dynamic model is confirmed by conducting simulation and comparing with the experimental data.Based on large eddy simulation and overlapping grid technique,a numerical simulation method of near-water-surface skipping motion of spinning disk is established.The multiphase flow characteristics of six-degree of freedom skipping motion of spinning disk are studied,and the flow field structure and flow mechanism of cavity evolution process are revealed.It is found that the spin velocity destroys the left-right symmetry of the cavity shape,the flow field and the pressure distribution at the disk bottom.The influence mechanism of initial inclined angle and spin velocity on the evolution characteristics of cavity and flow field is revealed.It is found that the velocity field and cavity have better symmetry in the skipping process for the disk with small initial inclined angle and low spinning velocity.Three main factors affecting the asymmetry of pressure distribution at the disk bottom are determined,including spinning velocity,roll angle and roll angular velocity.The evolution laws of the vertical and lateral hydrodynamic forces with the initial motion parameters during the skipping motion are obtained.According to the evolution of the vertical hydrodynamic force,the stages are divided during the collision time.The variation laws of lateral normal force and shear force with initial motion parameters are clarified,and it is found that the lateral normal force has a greater influence on the lateral deviation.The motion characteristics of a spinning disk with near-water-surface skipping motion are studied,and the effects of initial motion parameters on the attitude angle evolution and translational motion characteristics of the disk are obtained.The variation laws of oscillation ratio and frequency of inclined and roll angles with the initial motion parameters are clarified.The relationship between the maximum oscillation ratio of inclined angle and the number of impact stages in the skipping process is determined.Based on the results of continuous near-water-surface skipping motion of spinning disk obtained by the Moving Computational Domain method,five typical motion response modes in the longitudinal plane after the disk impacting the water are obtained.The empirical formula for predicting the maximum water entry depth of the disk based on the initial motion parameters is established.The influence law and mechanism of initial motion parameters on lateral deviation of disk are clarified.According to different parameter intervals of inclined angle and attack angle,the stable interval and linear interval of lateral deviation are established.The variation law of energy loss ratio with initial motion parameters in the motion process is given.The inclined angle of the disk with continuous near-water-surface skipping motion is optimized.By modifying the initial motion parameters,the empirical formula between energy loss ratio and dimensionless initial motion parameters is established,so that the prediction of energy loss ratio is realized.The inclined angle of the disk with near-water-surface skipping motion is optimized.By analyzing the displacement and hydrodynamic force of the disk during the collision time,the empirical formula between the energy loss ratio and the initial motion parameters is established,and the prediction of the energy loss ratio during the process of near-water-surface skipping motion of disk is realized.