Spectral analysis of a hypersonic boundary layer on a right, circular cone

Results from a stability investigation using quad-focused laser differential interferometry (q-FLDI) and high-speed schlieren cinematography of hypersonic flow over a cooled and uncooled 5^◦ half-angle cone are presented in this paper. The frequency and phase-speed of the largest-amplitude disturbance (largest N factor) as predicted by STABL and measured by FLDI or schlieren were in excellent agreement for the room-temperature cases and good agreement for the cooled-wall cases. A comparison between a cooled-wall and room-temperature shot at nominally the same Reynolds number shows the interesting result of the later transition to turbulence for the cooled-wall shot. Our hypothesis is: cooled-wall cases have higher growth rates and higher most-amplified frequencies. Because there is less wind-tunnel noise at higher frequency, transition will occur at a higher Reynolds number.