Polymer/Ceramic Pressure-Sensitive Paint with Reduced Roughness for Unsteady Measurement in Transonic Flow

Polymer/ceramic pressure-sensitive paints with reduced surface roughness were developed for measuring unsteady pressure fields in transonic flow. Four types of polymer/ceramic pressure-sensitive paints, each having different properties (such as particle size, mass content, and solvent), were formulated and applied to transonic wind-tunnel tests of a supercritical airfoil. The effects of surface roughness on the unsteady transonic flow on the airfoil were evaluated at Mach 0.74 at a Reynolds number of 5.0×106. It was found that all four polymer/ceramic pressure-sensitive paints could be used to measure time-series pressure distributions, but the location of the shock wave and the root-mean-square pressure fluctuations differed, depending on the type of polymer/ceramic pressure-sensitive paint. Among the tested polymer/ceramic pressure-sensitive paints, having an arithmetic surface roughness of 0.5 μm and a cutoff frequency of 3 kHz yielded practically the same data as a clean airfoil. Using this polymer/ceramic pressure-sensitive paint, propagation of pressure waves and oscillation of shock waves on the airfoil were clearly captured. A spectral analysis revealed that the fundamental frequency of shock-wave oscillation agreed very well with that calculated based on the mechanism proposed in previous studies. These results showed that the selected polymer/ceramic pressure-sensitive paint is an effective means by which to study transonic buffeting on airfoils and three-dimensional wings.