Particle image velocimetry (PIV) measurements were made in the center plane of a scramjet cavity flameholder to analyze the effects of simulated inlet flow distortion in the direct-connect test environment. Mach 3 non-reacting tests examined the effects of a full-span wedge configured such that an oblique shock impinged upon locations in and upstream of the cavity flameholder, including cases with wall-normal air injection upstream of the cavity to simulate fuel injection. Addition of flow distortion altered the size and shape of the primary recirculation region within the cavity by deflecting the bounding shear layer: the recirculation region was compressed by shock impingement upstream of the cavity, while shock impingement on the cavity itself expanded it. Air injection upstream of the cavity thickened the shear layer and produced a stronger effect on velocity direction than magnitude, preventing the formation of a large-scale recirculation region in two of the three shock locations studied. Flow distortion and air injection both increased flow unsteadiness, with the greatest increases in root-mean-square velocity occurring in the shear layer and above the cavity closeout ramp. At the most-upstream shock impingement location examined, flow patterns indicated fuel injected through the ramp at the center plane may not be recirculated within the cavity, providing a potential mechanism for a previously-observed lack of flameholding in this configuration. Additionally, results suggest the formation of spanwise secondary flow patterns that may account for flow nonuniformities observed in prior studies. This work presents the first PIV characterization of a scramjet cavity flameholder under distorted-flow conditions and with simulated upstream fuel injection.
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