Disturbance Level Characterization of a Hypersonic Blowdown Facility

Freestream disturbance levels were measured in the Mach 6 Hypersonic Wind Tunnel H3 of the von Kármán Institute, for unit Reynolds numbers ranging from 9.9 × 10^6 to 27.3 × 10^6 1/m. A detailed characterization was performed using a dual hot-wire anemometer probe operated in the constant temperature mode and a fast response pressure transducer mounted on the tip of a pitot probe. The disturbance levels measured by the two instruments indicated normalized fluctuating values of 5.2, 0.8, and 1.7%, respectively, for mass flux, total temperature, and pitot pressure. Statistical and spectral analyses were compared with data available in the literature and agreed with values obtained for other hypersonic wind tunnels working at similar ranges of Mach and Reynolds numbers. A combined data reduction technique allowed a complete analysis of the freestream flow. Normalized fluctuations of velocity, static temperature, and density were found to be 0.6, 5.2, and 4.9% respectively. Moreover, the dominant role of the sound-wave mode was observed in agreement with the features of conventional noisy hypersonic wind tunnels.