First results of lifetime-based unsteady PSP measurement on a pitching airfoil in transonic flow

The objective of the present study is to measure pressure distributions on a forced pitching airfoil using a lifetime-based pressure-sensitive paint (PSP) technique. Before the wind tunnel testing, fluorescence response of polymer/ceramic PSP to pulse excitation was measured at various pressures and temperatures. Relative timing and lengths of two gates were selected so as to reduce and measurement error based on obtained fluorescence response is reduced. The wind tunnel test was conducted in the JAXA transonic flutter wind tunnel at Mach number of 0.74. NASA common research model airfoil was pitched sinusoidally at a frequency of 30 Hz. A non-uniform lifetime distribution under a uniform pressure and temperature condition was observed on the model. The effect of non-uniform lifetime distribution could be canceled by normalization using a lifetime image under the wind-off condition. As a result, phase-averaged pressure distributions on the airfoil were successfully measured. Moreover, the measurement error for lifetime-based method is almost half of that for intensity-based method in the present measurement conditions.