Numerical Study On Characteristics Of Flow Field And Motions Of The Process Of Revolution Bodies Entering Water In Parallel

In the anti-mine warfare at sea,multiple projectiles are launched into the water in a very short time and space interval,which is a typical process of entering water in parallel.In this process,each projectile is highly susceptible to ballistic instability or even collision due to the coupling of multiphase flow field and projectile motion,which seriously reduces the strike efficiency.In this paper,the numerical calculation method is used to study the characteristics of the flow field and the motions of the revolution bodies in the process of entering water in parallel.The main research contents and results of this paper are as follows:Based on the momentum theorem and the angular momentum theorem,the dynamic differential equations of the revolution bodies entering water in parallel are derived.Based on the Reynolds time-averaged Navier-Stokes equation,the VOF multiphase flow model,Schnerr and Sauer cavity model and realizable k-? turbulence model are introduced,using the overlapping grid technique,a numerical calculation method for solving the flow field and motion parameters of water entry in parallel process is established,and the method is compared with the literature to verify the effectiveness.Numerical studies on water entry in parallel without cross flow under different initial velocity and initial clearance conditions were carried out.The characteristics of the flow field and the motions of the process of revolution bodies entering water in parallel without cross flow are analyzed,and the mechanism of the influence of initial velocity and initial clearance on the motion characteristics is revealed.The results show that the outer cavity develops freely and the development of the inner cavity is obviously limited.The heads of the rotation bodies are close to each other and the tails are far apart from each other,and the yaw motion has a promoting effect on the lateral motion;the greater the initial velocity is,the more obvious the expansion of the outer cavity is,the greater the limitation length is,the stronger the effect of head pressure on the lateral and yaw motions of the rotation bodies;when the initial clearance is small,the lateral and yaw motions of the rotation bodies are significantly restricted by lateral pressure difference.Based on the restrictive assumption of jerk,the lateral and yaw correction functions are introduced,and the prediction formulas for the lateral motion and yaw motion of the process of water entry in parallel without cross flow are derived.Two extreme motion states are given.Two criteria for extreme motion states are given,and strategies for avoiding motion instability are proposed.The results show that the motion state of the rotation bodies is determined by the shape of the rotation bodies and the initial conditions.In order to avoid instability,the initial velocity and the initial clearance should be within a reasonable range.The numerical study of the process of water entry in parallel with cross flow effect is carried out,and the after-effect flow field and motion characteristics of the monomer entering water with cross-flow effect are analyzed.Based on this,the flow field and the motion characteristics of the process of revolution bodies entering water in parallel with cross flow effect are analyzed.The results show that the outer cavity of the upstream revolution body and the cavity shape of the upstream side of the monomer are almost the same.The outer diameter of the cavity on the outer side of the backflow revolution body is smaller than the cavity diameter on the back side of the monomer.If the cross flow velocity is small,the heads of the revolution bodies are close to each other,but the tails are distant from each other.If the cross flow velocity is large,the heads of the revolution bodies are distant from each other,but the tails are close to each other.