Two-dimensional mathematical model of a propellant lined hypervelocity launch tube

Abstract

The problem presented in this manuscript is the formulation of a mathematical model of an explosive propellant lined hypervelocity projectile launcher. The model is used to perform a parametric study to assess the various aspects critical for proper operation of the Texas A&M University Hypervelocity Launcher. The hypervelocity gun considered herein differs from the classical gun in that the projectile ignites a thin coating of explosive on the inner surface of the gun barrel, thus causing a high pressure gas to be maintained near the projectile's base. The consequence is to provide a higher base pressure to the pellet, thus accelerating the projectile to higher velocities than otherwise obtainable in a conventional gun system. The course of action in this research was to review the literature and present the relevant theories, classical assumptions and techniques employed in modeling the internal ballistic phenomenon. The fundamental fluid dynamic equations were stated and rewritten in a second order finite difference scheme. The scheme was then formulated in an Eulerian, two dimensional hydrodynamic computer algorithm. The solutions to the algorithm for the various cases of the parametric study were obtained on a CDC 6600 computer at the Air Force Weapons Laboratory, Kirtland Air Force Base, New Mexico using the HULL system code. The model was verified by comparisons to the literature. Then the motion of the gas behind the projectile for the gas addition case was studied to determine its effect of increasing the pellet's velocity. A parametric study was performed to demonstrate the effects of wall propellant ignition delay times and initial driver gas conditions. Ignition delay times of 1 microsecond were found to be appropriate in the 15 kilometers per second velocity regime and 0.5 microsecond delays for the 30 kilometers per second regime. The most significant conclusion is that gas being added from the burning of a thin film explosive bore coating near the base of the moving projectile will increase the projectile velocity substantially over that obtained in a similar conventional hypervelocity gun system.