| The Joint Actinide Shock Physics Experimental Research (JASPER) facility utilizes a two-stage light gas gun to conduct equation of state experiments. The gun has a launch tube bore diameter of 28 mm, and is capable of launching projectiles at a velocity of 7.4 km/s using compressed hydrogen as a propellant. A numerical study is conducted to determine what effects, if any, launch tube exit geometry changes have on attitude of the projectile in flight. A comparison of two launch tube exit geometries is considered. The first case is standard muzzle geometry where the wall of the bore and the outer surface of the launch tube form a 90 degree angle. The second case includes a 26.6 degree bevel transition from the wall of the bore to the outer surface of the launch tube. The finite element method is employed to model the Euler equations and the compressible Navier-Stokes equations. The numerical method incorporates the use of trilinear, hexahedral, isoparametric elements, as well as the use of Petrov-Galerkin weighting applied to the advection terms. Mass lumping allows an explicit Euler scheme to be used in conjunction with a second-order Runge-Kutta approximation to advance the discretized equations in time. An h-adaptive mesh refinement scheme based on elemental flow feature gradients is utilized for greater solution accuracy. For both cases, solutions are calculated for several positions downstream of the launch tube exit. Numerical solutions obtained indicate that both cases will have an adverse effect on flight attitude of the projectile, with the beveled muzzle geometry performing worse than the standard case. |
