Numerical investigation of propellant leak methods in large-caliber cannons for blast overpressure attenuation

Abstract

In this study, we numerically investigate a novel means to reduce blast overpressure to the rear of a muzzle-loaded cannon. Reduction in blast overpressure, and thus peak overpressure, leads to an increase in the number of allowed rounds that can be fired over a given period of time for the crew manning the system. New propellant leak methods are studied using numerical simulations, where the propellant gas is intentionally allowed to leak in front of the projectile into the precursor region (while the projectile is still in the bore). This is done through the addition of a bulge or leak channels in the tube. The focus of this work is on a large-caliber muzzle-loaded cannon at $80^{\circ }$ (1,422 angular mils) elevation and with firing done at the max zone with the round and charge conditioned to ambient. We employ a hydrocode (ALE3D) to predict the blast overpressure for three types of geometries comprising five geometric configurations in total. These include one baseline configuration (i.e., with no modification) as well as four additional configurations with bulges and channels to allow propellant leak. The leaking of propellant gas into the precursor region leads to changes in the flow field associated with the precursor. In the case of channels, propellant leak results in a significantly reduced exit pressure ratio during projectile separation, and thereby, leading to a weaker primary blast wave. This in turn attenuates the peak overpressure to the rear of the muzzle without the aid of a muzzle device. For the channel leak method, at one monitored location, with the largest peak overpressure, a reduction of about 38 % was observed in peak overpressure as compared to the baseline case.