某大口径火炮发射弹丸启动压力研究

火炮发射时火药燃气压力将弹丸挤入炮膛，适当的挤进阻力能够减小初速或然误差、提高弹道一致性，是复杂的力学与火药燃烧耦合的过程。经典内弹道理论提出了启动压力假设，当火药燃气平均压力高于启动压力时弹丸开始运动，该假设导致启动压力物理含义不清楚、数值难以确定。本文以弹丸挤进过程和经典内弹道假设为基础，建立了弹底压力冲量与弹丸直线运动动量之间的数学关系，提出了弹底压力的冲量、截尾冲量与虚拟弹丸动量的关系。由于弹丸运动方程的积分形式更能反映出启动压力所具有的冲量物理意义，由此提出了一种确定弹丸启动压力的计算方法。以某大口径线膛火炮发射某榴弹为例，建立了弹丸挤进过程仿真模型，使用光滑粒子流体动力学法对某装药条件下弹带挤进过程进行了模拟，得到了挤进阻力和弹丸运动位移、速度等参数，采用本文提出的数值方法计算了等齐膛线和渐速膛线时弹丸启动压力。在以最大挤进阻力为特征点时，不同膛线形式对启动压力的数值有一定的影响，等齐膛线工况时的启动压力较渐速膛线时的启动压力略大。

A Study on Initial Pressure of Projectile Engraving Process for Large Caliber Gun

When gun firing,the projectile was pushed by into the chamber high pressure of propellant gas. Proper resistance force can reduce the initial velocity diversity and increase ballistic uniformity. The engraving process,which is a complex coupled process of mechanical and propellant combustion,is assumed that the projectile moves when gas pressure is greater than the initial pressure in the classic interior ballistics. This assumption results in that the physical meaning of initial pressure is obscure and cannot calculated directly. Based on the physical engraving process and classic interior ballistics,the relationship between projectile bottom pressure impulse and rectilinear motion momentum was proposed. It was defined that the pressure impulse subtracting the bottom pressure impulse equals to the virtual projectile momentum. Then,a calculation method for initial pressure was proposed based on integral form of the motion equation since it reflects the physical meaning of the intitial pressure. The engaving process of a large calibre gun was studied. A projectile engraving simulation model was proposed solved by smoothed particle hydrodynamics(SPH). The resistance force applying on the projectile by the gun bore,the movement and velocity of the projectile were obtained by simulations. Based on the proposed method,the initial pressure of guns with uniform and increasing rifles were calculated. At the characteristic point of maximum resistance force,different riling forms have certain influence on the value of initial pressure,the starting pressure of the uniform rifling condition is slightly higher than that of the increasing rifling condition.