Numerical simulation of the underwater gun using gas-curtain launch

Abstract

A novel gas-curtain launch technique is proposed to enhance the interior ballistic performance for underwater guns. The size of the initial gas curtain in front of the projectile is a critical factor in determining the subsequent behavior of the gunpowder gas jet flow field once the projectile leaves the muzzle. Hence, a validated two-dimensional unsteady multiphase model is built for the flow field at the muzzle of an underwater gas-curtain launch. The calculation involves determining the development of the initial gas curtain sizes for a 30 mm underwater gun, specifically focusing on the evolution of the precursor jet and gunpowder gas jet flow field. The results indicate that a double three-wave point structure forms within the bottle-shaped shock wave structure of the precursor jet when the initial gas curtain length equals the barrel. As the initial gas curtain size increases, the “bottle” structure elongates along the axial direction and compresses radially. After the projectile exits the muzzle, the gunpowder gas quickly expands toward the front, causing the collapse of the Mach disk of the precursor jet. The gunpowder gas jet then reforms a new bottle-shaped shock wave structure. A larger initial gas curtain can facilitate the expansion of the gunpowder gas, resulting in an increased size of the bottle, delayed formation, and weakened intensity of the Mach disk. Additionally, increasing the size of the initial gas curtain decreases the resistance experienced by the projectile outside the barrel. The initial gas curtain can also affect the cavitation bubble evolution process on the projectile sidewall, showing a growth-(attenuation)-stability trend.