Transition due to Roughness on Blunt Capsule: Comparison with Transient Growth Correlation

The effect of uniformly distributed surface roughness on the onset of boundary-layer transition for a capsule geometry was experimentally investigated in a conventional hypersonic blowdown wind tunnel. The thin-walled scale model of the Orion Crew Exploration Vehicle used in this study was mounted at a 28 deg angle of attack in the Adjustable Contour Expansion wind tunnel. A test matrix of 24 runs was developed to experimentally estimate the location of transition and to relate the flow properties at this location and the roughness height to established transient growth scaling. Tests were conducted for four different Reynolds numbers at six quasi-uniform surface roughness height distributions. The tunnel was nominally set to Mach 6.0 and a total temperature of 430 K for each run. Infrared thermometry was used to measure the surface temperature distribution. Heat transfer rates generated through a series of surface temperature maps were processed into normalized Stanton number centerline plots. These plots directly indicated the boundary-layer transition location. Analysis of the results indicated that the experimental data matched the established transient growth scaling.