Effects of Pressure-Sensitive Paint on Experimentally Measured Wing Forces and Pressures
Recent experiences with pressure-sensitive paint have shown that very thin paint layers on wind-tunnel models testedathighReynoldsnumberscansignie cantlyalterthepressuredistributions,andthustheforcesandmoments, on themodels.Thiswasobserved during two testsof transport-likewings:a “ clean” supercriticalwing at transonic cruise conditions in the NASA Ames High Reynolds Number Channel 2 and a high-lift wing, complete with slats and e aps, at landing conditionsin the NASA Ames 12-FootPressure Wind Tunnel. Theeffect of paint on the cruise wing was to displace the shock wave slightly upstream from its no-paint position. Smoothing the paint, and even removing it entirely from the leading edge, decreased this displacement slightly. Applying paint to only the slats of the high-lift wing caused the wing to stall prematurely at the highest Reynolds number. This effect could be eliminated by smoothing the paint. Adding paint to other parts of the model had little effect. Paint intrusiveness was much smaller and more ambiguous at lower Reynolds numbers. In both tests, paint intrusiveness occurred because the model surfaces were rougher when they were painted than when they were not, and this additional roughness altered the development of the turbulent boundary layers.