Instability and Transition due to Near-Critical Roughness in a Hypersonic Laminar Boundary Layer

摘要

Measurements of instability and transition were obtained in the wake of a cylindrical roughness within the laminar nozzle-wall boundary layer of the Purdue Mach-6 Quiet Tunnel. Using wall-mounted pressure transducers along the wake centerline, the root-mean-square pressure and power spectra were computed to find evidence of instabilities within the roughness wake. The roughness height was adjusted to explore the case of incipient transition on the nozzle wall. It appeared that small variations in the experimental parameters could have a large effect on transition for the near-critical case. Several dominant disturbance frequencies were identified for a range of conditions. These disturbances appear to be due to instabilities developing within the wake of the roughness. The streamwise evolution of these disturbances are reported, as well as the spanwise distribution at one streamwise location within the wake. These results can be used as a test case to continue to develop methods for computing the stability of roughness wakes.