Expansion Tube Experiments for the Investigation of Ram-Accelerator-Related Phenomena

Abstract

This paper presents the ISL expansion tube as a useful means for investigating the gas-dynamic phenomena occurring inside a ram-accelerator. It could be demonstrated that with a specially devised expansion tube, a combustible gas mixture can be accelerated to a superdetonative velocity without autoignition. The experiments in the expansion tube are carried out for basic research purposes on ram-accelerator-related combustion phenomena and also for supporting and optimizing the operation of the 30 mm and 90 mm ram accelerator facilities at ISL [1,2]. In this paper we discuss some experiments performed using the expansion tube. These experiments were carried out to demonstrate the establishment and stabilization of combustion at a step or a second small cone following the forebody cone. This second cone represents a small step on a projectile flying at hypersonic speed in an external propulsion accelerator, as proposed by Rom [3]. Using a modified CCD-camera we succeeded in recording the emission in the wavelength range 300 nm to 320 nm, emitted by the OH band “A ²Σ⁺ − X ²Π_i”. By this method we can measure the onset of combustion, its spatial extension and its duration. The experimental results are compared to fluid dynamics calculations using a CFD code that solves the 2D-axisymmetric, Reynolds-Averaged Navier Stokes (RANS) equations including equations for chemical kinetics (finite-rate and equilibrium), as given by Nusca [4].