Projectile Environment During Intermediate Ballistics,
NAVAL WEAPONS LAB DAHLGREN VA
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The development of the flow field associated with the ejection of a projectile from a gun may be broken into two phases. The first phase involves the flow induced by the projectiles in-bore travel, forcing the air initially in the gun tube to be ejected from the muzzle ahead of the projectile. In addition, leakage of high pressure propellant gases around the projectile due to imperfect obturation may occur during in-bore travel. The resulting gas flow ahead of the projectile forms the precursor free jet and blast field. The second phase results from the uncorking of the high pressure propellant gases as the projectile leaves the gun muzzle. The high pressure gases induce a strong traveling shock wave whose velocity initially exceeds the projectile velocity. The propellant gases expand from the muzzle as a highly underexpanded jet bounded by an oblique shock and Mach disc. The projectile must transverse through both the precursor blast field and propellant gas flow field before entering uniform exterior ballistic flight. Until recently, only limited success had been achieved in either calculating or measuring the blast or flow near the muzzle of a gun. This paper summarizes the development of numerical techniques for the computation of gun blasts.