Experimental measurements and numerical investigations of boundary-layer instabilities on a Mach 4.82 hollow cylinder

Experiments were performed on a hollow cylinder model at Mach 4.82 in an effort to understand the physics governing the boundary-layer transition process. Surface-based pressure sensors detail the transition process in a conventional Ludwieg tube wind tunnel from a laminar boundary layer to a turbulent one. Experiments span multiple unit Reynolds numbers and show second-mode growth that appears to be the dominant feature causing transition. Linear stability theory calculations show unstable second-mode frequency ranges that agree with those observed in experiments. Some spectral content from the experiments appears in a frequency range inconsistent with any boundary-layer instability predicted by linear stability theory. This could be due to tunnel noise or vibration. Possible second mode harmonics at twice the fundamental frequency were measured, showing signs of nonlinear activity. Plans for additional analysis and experiments that will include more diagnostics to characterize the dominant instability mechanisms are included.