Experimental and numerical research on a novel underwater launching method with high efficiency and low resistance

This paper describes an experimental and a numerical study of a recently developed high-efficiency, low-resistance launching method for an underwater launcher. The so-called gas-curtain launch method overcomes the problems of poor safety and low muzzle velocity in traditional fully submerged launchers. By introducing part of the gas inside the chamber to the front of the projectile, the water inside the barrel will be driven out. A low-resistance gas passage is then provided for projectile motion in the bore, thus delivering better interior ballistics performance than that in fully submerged launchers. Experiments are carried out using a 12.7-mm underwater launcher. A pressure sensor is used to record the chamber pressure, and high-speed video recordings allow the projectile motion around the muzzle to be determined. The experimental results show that the muzzle velocity is 172.8 m/s and the maximum chamber pressure reaches 116.0 MPa in a fully submerged launch, compared with a maximum chamber pressure of only 41.8 MPa and a muzzle velocity of 177.5 m/s when the gas-curtain launch method is adopted. The significant drag reduction effect of the gas-curtain launch greatly improves the interior ballistics performance, reducing the maximum chamber pressure by about 64.1% while retaining a similar muzzle velocity. Following the experiments, a numerical model is established and simulations are performed under various ventilation mass rates. The results clarify the drag reduction mechanism and the partial characteristics of the flow field in the gas-curtain launch.