The NTF is a high-pressure, cryogenic, closed-circuit wind tunnel that uses supercold nitrogen gas at high pressure to duplicate true flight aerodynamics. The NTF can accommodate models as small as one-fiftieth the size of an actual aircraft. Notable vehicles tested in the NTF have included the Boeing 777, the Space Shuttle and Booster, the Boeing 767, and blended-wing-body designs such as the B-2 bomber, the A-6 Intruder and the F-18 Hornet.
Unlike conventional wind tunnels, this facility can adjust airflow to match model size. The test section has 12 slots and 14 reentry flaps in the ceiling and floor to prevent any near-sonic flow “choking” effect. To ensure minimal energy consumption, the interior of the pressure shell is thermally insulated. The drive system consists of a fan with variable inlet guide vanes for responsive Mach-number control.
The NTF has two modes of cooling. In the first, variable temperature cryogenics, liquid nitrogen is sprayed into the circuit. The heat of vaporization and latent heat cools the tunnel structure and dissipates fan heat. In this mode, the NTF provides full-scale-flight Reynolds numbers without an increase in model size. Ambient-temperature air is the test gas in the second mode. Fan heat is removed by chilled water that flows through a cooling coil.
