Separation and Transition on a Cone-Cylinder-Flare: Experimental Campaigns

Experimental campaigns were conducted across three Mach 6 facilities on the hypersonic flow around a cone-cylinder-flare (CCF) geometry as part of the NATO STO Research Task Group AVT-346. Two conventional facilities (AFRL M6LT and ONERA R2Ch) and one quiet tunnel (Purdue BAM6QT) were used to test the same geometry and to study the instabilities in both the boundary layer and the shear layer above the axisymmetric separation bubble. Two nose tip radii (one nominally sharp and one blunt with a 5 mm radius) were tested. For the sharp nose tip case, there was excellent agreement between the measurements of both second-mode and shear-layer instabilities across the conventional facilities. However, the measured spectra for the blunt nose tip case showed more significant differences between the two conventional tunnels, potentially due to an alternate dominant instability mechanism coupled with the variations in the freestream noise spectra. The quiet facility resulted in a flow that remained laminar to much higher freestream unit Reynolds numbers, as well as in instability measurements that had more distinct spectral peaks for the sharp tip case and broadband rises for the blunt one. The instability mechanisms at play in the sharp quiet case were found to be the same as those in the conventional facilities.