Numerical Analysis of the Internal Ballistic Properties of Underwater Launched Gun with a Gas-Curtain

Abstract

When the gun submerged underwater is launched, the gun barrel is filled with water, which leads to much higher resistance in front of the projectile than that launched in air. So, the projectile acceleration decreases and the chamber pressure increases sharply so as to result in a burst barrel phenomenon. Base on this research background, this paper proposes the gas-curtain launch of underwater gun. Through a tiny hole opened in the projectile head, the powder gas is guided to inject into the front of the projectile to drain off water, which contributes to create a gas environment for projectile flight in the tube. Thus, the resistance before the projectile decreases to control the chamber pressure and improve the muzzle velocity. The paper designed a projectile with a central orifice for the 12.7mm machine gun and established the mathematical physical model for the gas-curtain launch to simulate and investigate the internal ballistic properties. The computational results show that, the gas-curtain launch of underwater machine gun can be achieved with appropriate variable-burning rate powder. Taking the internal ballistic performance of gun launched in air as reference, the underwater gas-curtain launch shows superior performance than the fully submerged underwater launch when the same charge quality is employed. The maximum chamber pressure and the muzzle velocity under the gas-curtain launch respectively are 86.5% and 81.6% of the situation launched in air, while the chamber pressure rises sharply to 298.9% and the muzzle velocity decreases to 71.2% under fully submerged underwater launch. The internal ballistic performance can be improved by adopting appropriate ventilation mass flow rate of 75.3 gs-1, which can ensure the fully expand of the gas jet to create a gas channel with lower pressure. At this time, the maximum chamber pressure can decrease to 85.2% while the muzzle velocity can rise to 85.5% of the gun launched in air. It can be found that the present gas-curtain launch for underwater gun can effectively improve the internal ballistic performance and it has vital academic and practical value.