| When the gun is launched underwater,the high temperature and high pressure gunpowder gas will eject rapidly after the projectile flies away from the muzzle to form the muzzle flow field.The underwater muzzle flow field is a kind of unsteady,multiphase flow which interacts with the moving projectile and contains a variety of shock wave structures.The gas-liquid interface of the gunpowder gas jet will have a great influence on the development of the muzzle flow field and the muzzle gas flow field will also cause disturbance to the projectile motion and thus affect the shooting accuracy.Therefore,it is of great significance to study the evolution mechanism of the muzzle flow field and its influencing factors to guide the underwater weapon experiments and improve the shooting accuracy of the weapon.This paper focuses on numerical simulation analysis combined with experimental verification methods to carry out numerical calculations on the muzzle flow field of the 14.5mm ballistic gun under different underwater launch conditions.The main research contents and results are as follows1)A two-dimensional axisymmetric numerical model was established to calculate the muzzle flow field of a 14.5mm machine gun under two different firing modes of constant pressure and variable pressure.The formation process and characteristics of the flow field at the mouth of the machine gun were compared and analyzed,the results show that the diameter of the Mach disc is larger than that of the variable pressure launch.With the continuous attenuation of the gunpowder gas,the structure of the gas flow wave system is clearer and more complete.The distance between the Mach plate and the center of the bore under two different launch conditions varies exponentially with time.2)A two-dimensional axisymmetric numerical model was established to calculate the muzzle flow field of a 14.5mm machine gun under the condition of no initial flow field under water and three different projectile muzzle velocities.By comparing and analyzing the numerical results,it was found that the initial formation time of the muzzle Mach number under three different muzzle velocities was basically the same,and the distribution of pressure and Mach number during the gas expansion process have certain rules.Numerical calculation was carried out for the muzzle flow field under the conditions of three different gas injection pressures of the 14.5mm machine gun.and the influence of pressure on the flow field characteristics of the muzzle flow field was studied.By comparing and analyzing the calculated results,it is found that the influence of pressure on the flow field has a certain rule.3)Through the numerical calculation of the muzzle flow field of the 14.5mm ballistic gun under different water depth conditions,the influence of the external environment(water depth)on the flow field characteristics of ballistic gun underwater launch muzzle is studied.The results show that with the continuous increase of water depth,the relatively large water pressure of the gunpowder gas during the expansion process makes the core area of the gas smaller and smaller,and the position of the Mach disc is closer to the bore;under three different water depth conditions,the Mach discs are exponentially distributed from the position of the bore;as the water depth increases,the temperature fluctuation of gunpowder gas decreases and the maximum value reached is higher. |
