Measurements in the Boeing/AFOSR Mach-6 Quiet Tunnel on Hypersonic Boundary-Layer Transition

Abstract

This paper presents results from four different research projects currently ongoing at Purdue University. (1) Different criteria for detecting the edge of the boundary layer were investigated on the flared cone geometry. It was determined that a method based on the total enthalpy profile would be used for future edge-detection computations on the flared cone geometry. A Rod Insertion Method (RIM) roughness insert was measured using a Zygo ZeGage optical profiler. Experimental results with a single RIM insert are presented. Maximum second-mode magnitudes of nearly 27% were measured 2.5 cm upstream from where spectral filling and intermittency algorithms compute that transition has begun. (2) Preliminary data from a new model shows that high-frequency secondary instabilities of stationary crossflow waves are localized under the troughs of the stationary vortices. Measurements of the growth of the secondary instabilities are reported for two different vortices. (3) In order to better understand the effects that probe geometry has on measured pressure fluctuations, pitot measurements were taken using various sleeves which alter the forward-facing diameter of the probe. The results indicate a clear effect of probe size on the measured power spectral densities. Furthermore, it was found that the geometry effects are Reynolds number dependent. (4) Experiments on a cone with a slice and ramp were completed to determine if transitional shock wave-boundary layers interactions can be measured within the Boeing/AFOSR Mach-6 Quiet Tunnel. Initial experiments showed that with a newly designed model it is possible to measure transitional interactions.

Measurements of Freestream Fluctuations in the NASA Langley 20-Inch Mach 6 Tunnel

“…For comparison, the other probes range from being a wire sensor 5-µm in diameter to a maximum of 6.35 mm in diameter for the PCB probe. Previous computational 34 and experimental 35 studies have shown that the geometry of pitot probes used can affect the measurement of freestream disturbances. It is possible that this peak is a result of an unsteady bow shock ahead of the larger probe body.…”