Experimental Study of Second-Mode Instabilities on a 7-Degree Cone at Mach 6

Abstract

Experiments have been carried out in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel to measure the second-mode boundary-layer instability on a 7° half-angle cone using high-frequency pressure sensors. Data were obtained with both blunt and sharp nosetips installed on the cone. The second-mode wave amplitudes were observed to saturate and then begin to decrease in the Langley tunnels, indicating wave breakdown. Pressure fluctuation measurements and thermocouple data indicated the location of transition along the cone at the different conditions tested. Comparisons between the power density spectra obtained during the current test and previous data from the Langley 15-Inch Mach 6 High Temperature Tunnel and the Boeing/AFOSR Mach 6 Quiet tunnel illustrate the effect of tunnel noise on instability growth and transition.