Experimental flameholding performance of a scramjet cavity with an inclined front wall

Abstract

This paper presents experimental data examining the flameholding performance of a scramjet cavity with an inclined front wall. Mach 8 flight-equivalent flows were delivered to the axisymmetric, cavity combustor via the T4 reflected shock tunnel. The combustor model was designed to permit interchangeable cavity geometries. Each examined cavity maintained a length-to-depth ratio of 4, with a depth of 8 mm and cavity close-out angle of 22.5 deg. The first examined cavity possessed a 90 deg front wall/step, while the second examined cavity inclined the front wall at 45 deg. Ethylene fuel was injected at a variety of mass flow rates to examine both scram-mode, jet-wake anchored and dual-mode combustion, with data measurements obtained via wall-mounted static pressure sensors. The steady nature of these combustion modes during the shock tunnel test time was demonstrated. Minimal differences in combustion-induced pressure rises were observed between the two cavity geometries across each fuelling condition. This indicates that the low pressure, quasi-stagnant region downstream of a 90 deg step is not essential to attaining robust flame-anchoring in a scramjet combustor. Chemically reacting, Reynolds-averaged Navier-Stokes computations were performed for the three dimensional combustor. Only minor mixing and combustion performance differences were noted between each geometry/fuelling permutation. It was noted that the 45 deg cavity retained more robust vortex structures within the cavity, with the 90 deg cavity seeing complete breakdown of the cavity vortex structures. This work indicates that the cavity front wall could be further modified with minimal impacts on flameholding performance.