Flight Simulation Characteristics of the Langley High Reynolds Number Cryogenic Transonic Tunnel

The theory and advantages of the cryogenic tunnel concept are briefly reviewed. The unique ability to vary temperature independently of pressure and Mach number allows, in addition to large reductions in model loads and tunnel power, the independent determination of Reynolds number, Mach number, and aeroelastic effects on the aerodynamic characteristics of the model. Various combinations of Reynolds number and dynamic pressure can be established to accurately represent flight variations of aeroelastic deformation with altitude changes. The consequences of the thermal and caloric imperfections of the test gas under cryogenic conditions have been examined and found to be insignificant for operating pressures up to 5 atm. The characteristics of the Langley 34 cm (13.5 in.) Pilot Cryogenic Transonic Pressure Tunnel are described and the results of initial tunnel operation are presented. Tests of a two-dimensional airfoil at a Mach number of 0.85 show identical pressure distributions for a chord Reynolds number of 8.6 X 106 obtained first at a stagnation pressure of 4.91 atm at a stagnation temperature of +120°F and then at a stagnation pressure of 1.19 atm at a stagnation temperature of -250°F.