Renewed characterization of a Mach 6 hypersonic wind tunnel

View Video Presentation: https://doi.org/10.2514/6.2023-1816.vid This paper presents a renewed characterization of a Mach 6 hypersonic wind tunnel. The H3 hypersonic facility, located at the von Karman Institute, is a blowdown-type wind tunnel with a useful test duration of the order of one second to one minute, currently equipped with a fixed-Mach, axisymmetric contoured nozzle. The H3 is a "cold" hypersonic wind tunnel, achieving high Mach numbers by lowering the speed of sound; it aims to replicate the Reynolds and Mach numbers commonly encountered by hypersonic vehicles in-flight. A test campaign assessing the full envelope of the testing conditions of the H3 is carried out. Some tests are performed at low reservoir temperatures to characterize the onset of condensation experimentally. For the first time, the free-stream static pressure in the H3 is assessed directly by the agency of a so-called Nagamatsu probe designed and optimized for operation within the facility. The impact pressure is measured with a classic Pitot probe. Free-stream Pitot and static pressures are measured simultaneously, along with reservoir pressure and temperature. Furthermore, the behavior of the flow around the probes is visualized via schlieren photography with a high-speed camera; the resulting pictures are used inter alia to retrieve the free-stream Mach number. CFD simulations of the flow in the H3 nozzle and around the static pressure probe are used to correct the data for viscous interaction effects. Then, different rebuilding techniques are implemented and critically compared to each other. The Mach number estimated from the static pressure probe output was found to be consistently inferior to the classical Pitot probe estimate, which could either be explained by the presence of non-isentropic phenomena in the nozzle or by a systematic error in the probe calibration, in particular in the viscous correction of the measured pressure. Nevertheless, the onset of condensation was detected successfully for operation with low stagnation temperatures.