Study On Flow Field Characteristics And Optimal Ballistic Trajectory Of Rotaional Mortar Projectials

To control the bullet dispersion and precision,low-speed rotation is used in mortar projectile which is a type of fin-stabilized projectile.However,the rotation would result in Magnus force and even reverse-Magnus force under some circumstances which would interfere the stability and precision of the projectile.Many challenges are produced by mortar projectile guiding system due to the demand of high overload,small size and low cost for the projectile,which to get a deep and comprehensive understanding about flow field and trajectory of the projectile.Therefore,the present study focused on the investigation in the flow field and trajectory of 120 mm satellite guided mortar projectile.As a result of complex structure of the mortar projectile,it was difficult to obtain detailed flow field structure surrounding the mortar projectile.Due to the cylinder configuration of the projectile profile,the study conducted CFD simulation of flow field surrounding a cylinder object based on large eddy simulation(LES)theory and Magnus force mechanism emerging in the rotation was investigated.The data obtained were further used to investigate flow field surrounding the rotating projectile,explore mechanism of the re-verse-Magnus force and then obtain aerodynamic parameters of the projectile.Moreover,the numerical studying of the whole process from the aerodynamic flow field to ballistic optimization are completed by solving the ballistic equation of six degree of freedom(6DOF).The main investigated contents and achievements of this dissertation are described mainly as follows:(1)The field characteristics and aerodynamic characteristics of flow past a roating cylinder at the subcritical and supercritical Reynolds number were investigated,and the mechanism of roating restrain the vortex shedding was revealed.The flow past a roating cylinder with different Reynolds number was investigated numerically,and the characteristics of the flow field structures under the condition of different Reynolds number and variation rule of drag andlift coefficients have been obtained.(2)The Magnus effect mechanism of flow past a roating cylinder at the subcritical Reynolds number has been studied.Our numerical calculations showed that the flow past a roating cylinder within certain range of Reynolds number and rotating speed will produce the inverse Magnus effect,and the main reason is that the turbulent boundary layer transition occurred on the side of the cylinder with its fluid moves opposite direction of the mainstream.Then,the separation point of this side is delayed,which leads to the decrease of pressure lift coefficient.However,this phenomenon will quickly disappear with the increase of rotational speed or Reynolds number.(3)The flow field structure characteristics and aerodynamic characteristics of the rotating projectile were studied based on the numerical simulation of Reynolds Average Navier-Stokes(RANS)and sliding grid technology.The inverse Magnus effect mechanism of low speed flight projectile has been revealed,its aerodynamic parameters have been calculated,and the numerical aerodynamic force coefficients have been compared and agree well with the results obtained from traditional engineering algorithm.(4)A new optimal guidance law which consider both the gravity compensation and avoiding the complicate nonlinear operation has been proposed and achieved.After the comparison with the proportion guidance law,optimal guidance law of large landing angel,its superiority has been shown to those satellite guided projectiles with limited ballistic control ability.Moverover,with the use of the Gauss pseudospectral method(GPM),the optimal trajectory with minimum overload and vertical attack is obtained.The numerical simulation of the whole flight process of the projectile from the aerodynamic flow field to ballistic optimization were achieved.