Thermodynamics of the ram accelerator

Abstract

Recent high‐velocity experiments with a ram accelerator are presented. The ram accelerator is a ramjet‐in‐tube projectile accelerator whose principle of operations is similar to that of a supersonic airbreathing ramjet. Different modes of combustion have been explored for accelerating projectiles of nearly identical geometry. Subsonic, thermally choked combustion theoretically allows a projectile to be accelerated to the Chapman‐Jouguet (C‐J) detonation velocity of a particular gas mixture. In the superdetonative regime the same projectile is accelerated while always traveling faster than the detonation velocity, and in the transdetonative regime (85–115% of detonation velocity) the same projectile may transit smoothly from a subsonic to a superdetonative combustion mode. This paper examines operation in these three regimes of flow up to velocities approaching 2500 m/s. Experimental evidence of acceleration in the transdetonative and superdetonative regimes is introduced. A computational fluid dynamics (CFD) code is being developed for studying the flow, combustion, and performance of the ram accelerator, particularly in the superdetonative regime. The code solves the 2D/axisymmetric Euler equations with coupled chemical nonequilibrium processes using a shock‐capturing technique and gives theoretical results showing efficient acceleration of projectiles is possible through velocities as high as 9 km/sec.