Mixing and Mass Exchange for Cavities in Supersonic Flows

Abstract

The ability of wall-mounted cavities to facilitate flameholding is largely dependent on local conditions within the recirculation region, that are, generally, vastly different from the adjacent supersonic flow. The local stoichiometry depends on the mixing within the flameholder and the mass exchange with the core flow. These processes are integrally linked to fuel injection location and its coupling with the recirculation region flow field. In the present study planar laser-induced fluorescence (PLIF) was used to obtain a twodimensional image of the streamwise fuel distribution in a non-reacting, directly-fueled cavity in a Mach 2.2 flow. Fuel was injected from two different locations within the cavity chosen to result in parallel and counterflow mixing with respect to the primary cavity circulation. Injection from both locations resulted in a largely fuel rich recirculation region. Parallel injection from the cavity step was characterized by pooling of fuel within the cavity’s trapped vortices with the majority of mixing occurring in the shear layer and along the cavity walls. Counterflow injection from the cavity floor resulted in a leaner flow field attributed to enhanced mixing with the impinging shear layer, larger quantities of fuel escaping the recirculation region and limited mass exchange between the trapped vortices. The local concentration fields generated by both fueling schemes suggested that under analogous reacting conditions the region around the shear layer would serve as the most probable flame anchoring location.