Second-Mode Transition on Flared Cone In Mach-6 Quiet Flow

Hypersonic boundary-layer transition was characterized on a flared cone geometry in the Boeing/AFOSR Mach-6 Quiet Tunnel. Experiments in low-disturbance, quiet flow at five unit Reynolds numbers from [Formula: see text] to [Formula: see text] measured a hot–cold–hot streak pattern with azimuthal wave numbers between 75 and 90. Pressure fluctuation measurements captured the second-mode instability nonlinearly amplifying and saturating before fundamental breakdown to turbulence occurred. The average peak heating in the streak pattern was [Formula: see text], and the average maximum second-mode fluctuation magnitude before breakdown was 31.6%. The maximum amplitude before breakdown is more than double what is predicted using data from experiments performed in conventional hypersonic facilities at similar edge Mach numbers. An average [Formula: see text]-factor of 14.5 was calculated when the second-mode instability saturated at its greatest amplitude, which is within 10% of the [Formula: see text]-factor calculated for the recent HIFLIER flight experiment. This is the first time that an [Formula: see text]-factor has been reported for second-mode dominated transition in a low-disturbance facility and the first comparison to second-mode transition data obtained during a flight test. The experimental results provide a data set for future computations of nonlinear growth, saturation, and breakdown of the second-mode instability in a low-disturbance, quiet flow facility.