A Research Program for the Development of a True-Temperature Mach 8-15 Medium-Scale Hypersonic Wind Tunnel*

There is a need for the United States to develop flight vehicles that fly at hypersonic speeds in the atmosphere, serve as transporters for space access, and have capabilities of fast response, global reach, and missile defense. Currently, the development of these various flight vehicles is constrained by the lack of ground-based test facilities, which are considered necessary to provide affordable development testing and reduce technical risk to acceptable levels. Especially, the U.S. does not have adequate test facilities that can be employed for development, qualification, and operational testing of air-breathing propulsion flight systems at the necessary flight simulation conditions above Mach 4. Technologies are available for building adequate development and qualification test facilities to Mach 7, but not beyond where some systems would fly to perhaps as high as Mach 20. It is critical that the environment of hypersonic flight be simulated and actually duplicated for most cases in terms of velocity, temperature, pressure, air chemistry, scale, and test time for air-breathing propulsion testing. This generally is the most difficult challenge compared to, for example, aerodynamic, aero-thermal, and aero-optic testing because of the non-scalable combustion processes involved. To date, technologies for duplicating hypersonic flight environment in wind tunnels above Mach 7 have not been satisfactorily developed for applications such as air-breathing propulsion testing. Electric arcs, combustion heating, and compression heating have been employed to heat the test gas in a stagnation chamber and expand the test gas through a nozzle throat to the desired velocity. All these energy addition techniques involve one or more serious deficiencies: short run time, unacceptable gas chemistry, and entropy and/or velocity mismatch. For all, practical run times are limited by materials capable of withstanding the requirements of high stagnation temperature and pressure, especially with respect to nozzle throat heat transfer and survivability. In an attempt to overcome most if not all of these deficiencies, the U.S. Air Force (USAF) is sponsoring the RDHWT/MARIAH II (Radiantly Driven Hypersonic Wind Tunnel/with magnetohy drodynamic augmentation) research program. The program is designed to develop enabling technologies and design criteria leading to the design, fabrication, and operation of a Medium-Scale Hypersonic Wind Tunnel (MSHWT) with Mach 8-15 truetemperature test capabilities and adequate run time.