Onset of condensation effects with a NACA 0012-64 airfoil tested in the Langley 0.3-meter cryogenic tunnel

A 0.137m airfoil was tested in a 0.3m transonic cryogenic tunnel at free stream Mach numbers of 0.75, 0.85, and 0.95 over a total pressure range from 1.2 to 5.0 atmospheres. The onset of condensation effects were found to correlate more with the amount of supercooling in the free stream than it did with the supercooling in the region of maximum local Mach number over the airfoil. Effects in the pressure distribution over the airfoil were generally seen to appear over its entire length at nearly the same total temperature. Both observations suggest the possibility of heterogeneous nucleation occurring in the free stream. The potential operational benefits of the supercooling realized are presented in terms of increased Reynolds number capability at a given tunnel total pressure, reduced drive fan power if Reynolds number is held constant, and reduced liquid nitrogen consumption if Reynolds number is again constant. Depending on total pressure and free stream Mach number, these three benefits are found to respectively vary from 7 to 19%, 11 to 25%, and 9 to 20%.