The European Transonic Wind Tunnel (ETW) is similar to the National Transonic Facility, a pressurized cryogenic, closed circuit, continuous-flow, fan-driven wind tunnel. It can be operated in closed and slotted wall configurations for testing full and half-models from Mach numbers of 0.15 up to light supersonic conditions at M_∞=1.35. Pure high quality nitrogen is used as the only test gas. The capability of varying the gas temperature, pressure and speed independently allows for pure Reynolds number and/or aeroelastic investigations. The test section dimensions are 7.87 ft (2.4 m) in width, 6.56 ft (2 m) in height and about 30 ft (9 m) in length. High flow quality is provided by 2 filling screens in the wide angle diffuser combined with a flow straightener (honeycomb) and 2 anti-turbulence screens followed by a fixed contraction and a flexible nozzle for supersonic operation. Additionally, the tunnel features a second throat downstream of the re-entry preventing flow disturbances eventually generated in the high-speed diffuser from propagating upstream into the test-section.

The ETW operating range covers pressures from 110kPa to 450kPa and temperatures from 313K down to 110K allowing the achievement of maximum Reynolds numbers of 50 million for full models and 90 million for semi-span models at a Mach number around 0.85. While the tunnel shell is internally insulated against heat losses the heat generated by the fan is compensated by the evaporation of the injected liquid nitrogen, which is sprayed into the tunnel upstream of the compressor. Further details about the facility and its operation can be found at www.etw.de.