Cryogenic pressure sensitive fluorescent paint systems

In recent experiments, we demonstrated the feasibility of using luminescent coatings for surface pressure measurement in a cryogenic wind tunnel. Numerous PSP samples were calibrated and a new coating technology in which luminescent molecules are directly deposited onto an anodized aluminum model surface was developed. The resulting coating has an extremely high oxygen sensitivity for mole fractions of oxygen less than 0.1%. Cryogenic pressure calibration techniques are discussed and calibration curves presented. To demonstrate this technology, a 14%- thick bump model was tested in the 0.1-m Transonic Cryogenic Wind Tunnel at NAL. Mach number was changed from 0.4 to 0.84 whereas temperature was maintained at 100 K. A small amount of oxygen was injected into the tunnel and the mole fraction of oxygen (250 PPM)in the test gas was kept constant. The results using an in situ calibration for the paintderived pressure distributions are in good agreement with pressure tap measurements.