Boundary-layer transition was measured on a pitched, 7° half-angle cone in a Mach 8 conventional wind tunnel. On a smooth cone, transition via second-mode waves was observed at all angles of attack. In addition, naturally-excited stationary crossflow waves were apparent in temperature sensitive paint images, but did not appear to lead to transition. Two patterns of roughness elements were used to generate higher-amplitude stationary crossflow waves. Breakdown of the stationary waves was observed. The roughness resulted in instability amplitudes nearly an order of magnitude larger than the smooth cone at the same Reynolds numbers and higher instability growth rates. Transition occurred 30% -40% sooner using the roughness elements with peak amplitudes near 15 - 20%, for α ≥ 4°. A low-frequency, coherent wave was measured at all angles of attack. The calculated phase velocity shows a strong dependence on angle of attack, but the propagation angle is similar for all non-zero α. The measured wave properties are curiously similar to measurements of a suspected tunnel-noise-driven instability made on an elliptic cone at Mach 6.
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