Numerical Investigation On The Dynamic Sabot Discard Process Of APFSDS

The dynamic discard process of sabots of the armor-piercing,fin-stabilized discarding sabot(APFSDS)is extremely complex and highly transient,and their attitudes can be myriad.Furthermore,the sabots are strongly coupled with the projectile and affect the free flight of the projectile.Although the APFSDS are used widely all over the world,their dynamic discard process is not still adequately understood,which induce some defects.On the other hand,with the rapid development of computational fluid dynamics(CFD),it is possible to use CFD to investigate numerically the detail characteristics of the dynamic discard process.Therefore,it is very important to investigate numerically the discard and the motion process of the sabot for improving the performance of the existed products and designing the next generation of APFSDS.The main investigated contents and achievements of this dissertation are described mainly as follows:Based on the coupling of the governing equations of fluid dynamics and rigid body motion equations of six degree of freedom(6DOF),with the use of the adaptive mesh refinement technique for gradient of pressure and the improved dynamic mesh technique,and the high-order AUSM+ scheme,the 3-D compressible flow governing equations were solved numerically.Furthermore,the Runge-Kutta method and fourth-order multi-point Adams-Moulton formulation were employed to solve the 6DOF equations.The numerical method for simulating the 6DOF flight of the 3-D morph projectile was obtained.The quality and deformational ability of meshes generated were enhanced by the introduction of the spring constant factor and the spring constant,the numerical diffusion induced by the interpolation among meshes was also reduced,which can improve the capturing ability of shock wave of the flow fields.The developed numerical method was used for the numerical design of the hollow projectile,and the numerical simulation of the missile separated from the aircraft and the extend deformation of the APFSDS during the flight process.The numerical results verified the feasibility of the method and its capturing ability of the shock wave as well as the 6DOF movement of projectile.The dynamic sabot discard process of APFSDS under ideal and no disturbance condition was investigated numerically.The results showed that the flow field modifies sharply with the change of the attitudes and positions of the sabots with respect to the projectile.The sabot discard process can be divided into three phases based on their interactive actions and respective flow features.The first stage occurs at the beginning of discard,the high-speed flow accumulates at the front of the sabot due to the small gap between the sabots and projectile and the bow shock of sabots appears.With the increase of the gap,each bow shock impinges on the projectile and reflects back and forth.The flight stability of the projectile is affected by the high pressure which is induced by the impinging.With further increase of the gap,the interaction between the sabot and projectile become weak,and the tail of the projectile is still under the action of oblique shocks of the sabots,however,the shock wave reflection is weak and ultimately has no effect on the projectile.The analysis of the projectile aerodynamic coefficients showed that the aerodynamic interference was the largest one of the disturbance sources during the sabot discard process.The influence of the initial disturbance and meteorological wind on the sabot discard process of APFSDS was also simulated numerically.The details of the flow fields in different sabot discard process,6DOF motion parameters and associated aerodynamic parameters were also obtained.Numerical results showed that it is similar for the dynamic sabot discard process under no disturbance condition,and the process can be also divided into three phases,however the process of the interaction between each sabot and projectile differs,the impact of each sabot on the projectile was no longer synchronized and the discard of each sabot was no longer symmetrical.The variation of the projectile aerodynamic coefficients increases,thereby the effects on the stability of the projectile become larger.Numerical simulation of the effect of the high pressure underexpanded gas near the muzzle on the sabot discard of APFSDS was conducted,and the whole process of the highly underexpanded jet chases the APFSDS and eventually passes through the jet was clearly described.Our results showed that the sabot discard is dominated by hypsokinesis before the gas catching the sabot,and it leans forward when the gas moves to the button of the sabot.The radial force and negative pitching moment generates due to the high-pressure zone formed at the tail of the sabot.When the sabot passed through the gas stream,the angular motion of the sabot returned to previous state.Therefore,the upturn movement of the sabot was not obvious and it almost parallel to the projectile during the discard process.The changes of 6DOF movement of the sabot are larger than the projectile due to the effect of the gas,and it is helpful for the sabot discard.In addition,the projectile produced a smaller rotation rate at the action of the gas,which can increase its flight stability of the projectile,and the pitch and yaw angles of the projectile are small.