Surface flow and PSP measurements in the large-scale low-boom inlet

The local flowfield effects of vortex generators on a supersonic axisymmetric relaxed external compression inlet have been investigated with surface flow visualization and pressure-sensitive paint measurements in the 8'×6' supersonic wind tunnel at NASA Glenn Research Center. This inlet entails a mechanically simple design for providing a high-recovery/low-distortion flowfield and low sonic boom signature. A set of vortex generators was incorporated into the design both upstream of the terminating normal shock and downstream inside the subsonic inlet diffuser for decreasing separation near the shock/boundary layer interaction and reducing radial distortion at the engine face, respectively. The inlet centerbody and downstream diffuser vortex generator regions were imaged during wind tunnel testing internally through the inlet cowl with a camera housing attached to the cowl. The surface flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody, vortex generators, and struts were measured.