装药参数对水下机枪密封式膛口流场影响的数值分析

Numerical Analysis of Influence of Charge Parameters on Flow Field around Sealed Muzzle of Underwater Machine Gun

为了研究装药参数变化对水下机枪密封式发射膛口流场特性的影响,建立了水下机枪密封式发射的数学物理模型。运用流体力学计算软件Fluent,结合用户自定义函数和动网格技术,针对12.7 mm滑膛式机枪,分别采用15.5 g、13.0 g和11.0 g装药量对其水下密封式发射膛口流场进行了数值模拟。计算结果表明:不同装药量条件下,水下机枪密封式发射时,在弹头飞离膛口截面的过程中,水对弹前初始空气和弹头轴向运动的阻碍较大,导致弹头减速、火药燃气在弹后空间聚集、膛口燃气压力升高,而火药燃气形成射流后的喷射压力衰减遵循指数衰减规律;膛口射流形态受弹头速度和燃气喷射压力的耦合影响,均逐渐由梯形空腔转变为葫芦状空腔,且射流的轴向最大位移遵循指数衰减规律,马赫盘的初步形成时间也基本一致;随着弹头初速和燃气初始喷射压力的降低,火药燃气在射流头部聚集且径向扩展明显,并伴随形成二次射流,而弹底对马赫盘形状的影响时间缩短,激波核心区结构也更快地接近于正激波。因此可见,装药量对膛口流场分布的影响具有一定的规律性。

A mathematical-physical model is established to study the influence of charge parameters on the flow field characteristics for 12.7 mm underwater machine gun.Fluent software,combined with userdefined function and dynamic grid technology,is used to simulate the flow fields around the sealed muzzles of underwater machine guns with the charge quality of 15.5 g,13.0 g and 11.0 g,respectively.The results show that the axial movements of initial air and projectile are impeded by the high-density water,resulting in the slowdown of projectile and the gathering of gunpowder gas at muzzle during the projectile flying through the muzzle.The attenuation of gas jet pressure follows the exponential decay rule after a projectile is fired from the muzzle.When the jet is affected by both the projectile velocity and the gas jet pressure,its shape gradually changes from a trapezoidal cavity to a gourd-like cavity,and the maximum displacement of jet follows the exponential decay rule.The initial formation time of Mach disk is basicallythe same for the three charge conditions.With the reduction in the initial velocity of projectile and the initial injection pressure of gas,the gunpowder gas gathers in the jet head and radially expands to form the secondary jet.Meanwhile,the impact time of projectile base on the shape of Mach disk is shortened,helping the shock core faster approximate to normal shock wave.It can be seen that the influence of charge quality on the distribution of the flow field around the muzzle has a certain regularity.