Issues Concerning Computational Analysis of the Ram Accelerator Starting Process D. L. Buckwalter* Wright Laboratory Wright Patterson AFB, Ohio 45433-7251 and C. KnowlerT and A. P. Bruckner* Aerospace and Energetics Research Program University of Washington, Box 352250 Seattle, Washington 98195-2250 Abstract I. Introduction A 2D/axisymmetric computational fluid dynamics code is being created to analyze the starting process of the ram accelerator. In particular, the current analysis investigates the gas dynamics in the launch tube created by the projectile/obturator combination traveling towards the first ram accelerator tube. Computational analysis of this process provides numerous challenges due to the moving boundary conditions, the strong shock reflections off the solid boundaries, and the impulsive motion of the projectile. Other difficulties arise while maintaining a computational grid to accurately capture shock phenomena. The research has shown that the starting process can be modeled, and investigated, by utilizing a numerical scheme that includes a heat conduction mechanism to reduce wall heating due to strong reflected shocks. It was also found that the computational time per solution can be greatly decreased by careful manipulation of the grid points at each time step. The current research code is capable of using either a second order Roe or a first order Marquina flux solver. During the early stages of projectile motion, the Marquina solver was the more robust of the two, but was too dissipative to provide a complete detailed analysis. A higher order version of the Marquina scheme shows promise that it can be used to analyze the complete starting process of the ram accelerator. Aerospace Engineer, currently a graduate student at the University of Washington, Student Member AIAA. 1 Research Scientist, Senior Member AIAA. ? Professor and Chair, Fellow AIAA. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. The ram accelerator is a chemically driven mass launcher that has accelerated projectiles up to speeds of 2.7 km/s in the University of Washington (UW) facility. The ram accelerator is a ramjet-in-tube concept in which a subcaliber projectile travels through a stationary tube containing a high pressure fuel and oxidizer mixture as shown in Fig. 1. As the projectile Tube Wall Normal Combustion Conical Premixed Shock; Fuel/Oxidizer M: ,v.ii$iiJ Thermal llllill Choking <l" '''Iff M=1 Fig. 1. Ram accelerator operating in the thermally choked propulsive mode. travels supersonically through the tube, the propellant is compressed and heated by a series of shocks originating from the projectile nose. Behind the projectile, the propellant combusts and expands to produce thrust. Details of the theoretical operation of the ram accelerator have been well documented and will not be presented here. A typical ram accelerator system consists of a prelauncher, the ram acceleration section, and a deceleration section. A schematic of the University of Washington's 38 mm ram accelerator facility is shown in Fig. 2. It uses a light gas gun as a prelauncher and typically accelerates the projectile from rest up to speeds of 1100 m/s, prior to entering the ram accelerator American Institute of Aeronautics and Astronautics