Disturbance Level Characterization of a Hypersonic Blowdown Facility

Free-stream disturbances have a dominant role on boundary layer stability and transition, especially in high speed ows. The assessment of the ow quality in a wind tunnel is therefore a key issue especially in transition to turbulence studies. With this purpose a detailed characterization of the free-stream disturbance level of the VKI H3 Mach 6 Wind Tunnel at di erent Reynolds number is carried out by means of classical intrusive measurements techniques (hot-wire anemometry and Pitot pressure probes). Issues concerning the aerodynamic heating of the probes are investigated and a special calibration technique is developed in order to compensate for these e ects. Statistical and spectral analyses are compared with the data available in the literature for other hypersonic wind tunnels, working at similar ranges of Mach and Reynolds numbers. A combined data reduction technique is also developed which allows to extract all ow quantities uctuations from those directly measurable through the above-mentioned instrumentations. By means of this technique, the validity of some physical hypotheses on the ow can be veri ed. Moreover, a Kovasznay modal analysis allows to characterize the origin of the disturbances.