Cavity-based flameholding for chemically-reacting supersonic flows

Recesses in the walls of supersonic combustion chambers - cavities - have emerged as a preferred flameholding device since they are non-intrusive, hence resulting in reduced drag, lower total pressure losses and minimal aerodynamic heating when compared with other means of piloting core combustion such as, for example, struts. The flowfield within and in the vicinity of a cavity is complex involving a strong coupling between hydrodynamics and acoustics. When employed as a flameholding device both fuel injection and heat release - which is closely coupled to local mixing processes - alter the flowfield and further complicate the interaction between the cavity and the core supersonic flow. The complexity of this flowfield makes the identification of the dominant flameholding mechanisms and prediction of flame stability limits substantially more difficult than in the case of premixed systems. The following sections review the current knowledge of the mechanics of cavity-based flameholding in supersonic flows. Aspects of the non-reacting and reacting cavity flowfield are discussed with particular emphasis on the impact of fuel injection location relative to the flameholder. Results obtained to date in the attempt to describe the operability of cavity flameholders in terms of experimentally determined flame stability limits are also presented. (C) 2015 Elsevier Ltd. All rights reserved.