Study On Aerodynamic And Ballistic Characteristics Of Base Bleed Projectile And Numerical Simulation Of Its Base Flow Field

With the improvement of precision of artillery and the development of modern tactics and techniques,it becomes more important to extend artillery range.In many ways of extending artillery range,base bleed method is widely used by many countries because of its simple construction and high extend-range rate.Base bleed method achieves the purpose of decreasing drag and extending range by bleeding mass and energy into the low pressure area and then increasing the pressure of projectile base.Some results of key techniques about base bleed projectile has been formed.However,problems about optimization design of base bleed parameters,as well as problems about calculation and analysis of base flow field with high speed rotation and its influences for drag reduction,has been studied little.For this purpose,high speed rotating base bleed projectile is used as the research object in this thesis,with several respects have been researched and analysed,such as influences of parameters for drag reduction characteristics,optimization of base bleed parameters,numerical simulation of base flow field and aerodynamics characteristics.(1)The mechanism of drag reduction of base bleed projectile has been analysed,and its internal and external ballistic models have been established.By analysing the burning mechanism of base bleed grain and using methods such as formula derivation,internal trajectory equation set of base bleed was established.Based on the analysis of force and moment effect on base bleed projectile,6 DOF rigid body trajectory equations were derived according to Newton's second law and the moment of momentum theorem.The internal and external ballistics equations were then combined to establish the trajectory calculation model of base bleed projectile.(2)The influences of base bleed parameters for drag reduction characteristics has been studied.Using the established model,trajectory calculation was undertaken to a certain type of base bleed projectile as an example.Influence of several parameters for the trajectory characteristics of this projectile was compared and analysed,which are the burning rate cofficient,the diameter of bleed nozzle and the length,inner diameter and the section number of the grain.(3)Base bleed parameters optimization has been done for base bleed projectile with the maximum range as the objective function.There are 5 parameters selected as the design variables,which are the burning rate cofficient,the diameter of bleed nozzle and the length,inner diameter and the section number of the grain.Range was selected as the objective function,with some constraint conditions set up.Based on the advantages and disadvantages of genetic algorithm and particle swarm optimization,a new algorithm named genetic particle swarm optimization algorithm,with faster optimization speed and higher precision,was designed as intelligence algorithm in the process of optimization.Thus,the parameters optimization design model of base bleed projectile was established and used in the base bleed parameters design.(4)The numerical simulation of base flow field has been done,and its influences for the drag reduction has been analysed.Adopting methods such as sliding grid,numerical simulation model was established and used to simulate and analyse the base flow field of base bleed projectile,with the condition of no rotation and high speed rotation.With no rotation,the influence of the bleed parameter,the flow Mach number,muzzle and high altitude environment for the base flow field and aerodynamics characteristics was researched.More important,with high speed rotation,the influence of rotating speed,bleed parameter and their mutual restriction relation for the base flow field and aerodynamics characteristics was researched.