Aerodynamic Characterization of a Cavity Flameholder in a Premixed Dual-Mode Scramjet

Particle image velocimetry was performed in the spanwise centerplane of a scramjet cavity flameholder under premixed hydrocarbon-fueled dual-mode conditions, providing the first reported results of their kind. Graphite tracer particles were shown to offer suitable aerodynamic performance and durability in a high-enthalpy flow, overcoming restrictions on measurement duration due to window degradation by metal oxide tracers used in prior investigations. A precombustion shock system was recreated, independent of heat release, through use of an air throttle, allowing the effects of combustion to be decoupled from upstream aerodynamics. The mean velocity field was found to be affected more by the configuration of the shock system than the presence or amount of heat release. The velocity variance and the strength of the turbulent eddies were also a strong function of shock system configuration under adiabatic conditions, but they took reduced levels once combustion was established and were nearly invariant with subsequent changes to the fueling rate and shock system. A comparison of turbulent velocities with planar laser-induced fluorescence imaging of the Hydroxyl radical indicated main-duct combustion was piloted by the intermittent transport through the shear layer of products generated in the cavity interior.