Non-intrusive unsteady PSP technique for investigayion of transonic buffeting

In this study, transonic buffeting phenomena on a 2D airfoil and a 3D transport wing were analyzed with unsteady pressure-sensitive paint measurement. Polymer/ceramic PSPs with low surface roughness were applied to 2D- and 3D-Common Research Models in order to measure unsteady pressure distributions without intruding the flows. Unsteady pressure fields on the 2D airfoil were evaluated at Mach number of 0.74 and chord Reynolds number of 5 × 10⁶. Pressure waves moving upstream at the angle of attack of 3° and a periodic shock oscillation under buffeting condition were clearly measured. A spectral analysis showed that the fundamental reduced frequency of the shock oscillation was 0.42 at the angle of attack of 6°. To demonstrate the effectiveness of unsteady PSP measurement on a 3D transport wing, wind-tunnel testing was conducted at Mach number of 0.85 and chord Reynolds number of 1.54 × 10⁶. Pressure time histories and their spectra measured by the PSP agreed well with those obtained by an unsteady pressure transducers. Under the off-design conditions, complicated shock oscillations on the swept wing were observed. These results indicate that the PSPs can offer a powerful means to investigate transonic buffeting on aircraft.