Numerical analysis of the influence of water/air medium on the muzzle flow field characteristics of machine gun

The mathematical and physical model for underwater sealed gun is established to investigate the flow field distribution characteristics for gun muzzle in different mediums. The muzzle flow field for the 12.7 mm gun which is sealed launched underwater is numerically simulated by combining User-Defined Functions (UDF) and dynamic grid technique. The predicted results show that, the muzzle flow field for gun launched underwater is significantly different with that for in air. Unlike that the initial air forming bottle shock wave at the muzzle for gun launched in air, it hits the gas-liquid interface with forming series cylindrical compressed wave in the area before the projectile for gun sealed launched underwater. As the gunpowder gas sprays out, Mach disk appears at 60μs after the projectile shot into water. Meanwhile, the shape of shock waves is fusiform and then turns into a peach heart gradually. However, the bow shock for gun launched in air, which is affected by the projectile base with its structure being bowl-shaped, fails to develop into the Mach disk at even 160μs. Compared with gun launched in air, the muzzle shock wave area for gun launched underwater is obviously smaller.