Polymer/Ceramic PSP with Reduced Surface Roughness for Unsteady Pressure Measurement in Transonic Flow

Abstract

Polymer/ceramic pressure-sensitive paints (PC-PSPs) with reduced surface roughness were developed for measuring unsteady pressure fields in transonic flow. Four types of PC-PSPs, each having different particle size, mass content, solvent, and so on, were formulated and applied to transonic wind-tunnel tests of a Common Research Model airfoil. The effects of surface roughness on unsteady transonic flow on the airfoil were evaluated at Mach 0.74 and Reynolds number of 5.0 x 10 6 . It was found that all four PC-PSPs had capabilities to measure time-series pressure distributions, but the location of a shock wave and the root-mean-square pressure fluctuations differed depending on types of PC-PSP. Among all tested PC-PSPs, the PC-PSP having arithmetic surface roughness of 0.5 μm and cutoff frequency of 3 kHz yielded data practically the same as that of a clean airfoil. Using this PC-PSP, propagation of pressure waves and oscillation of shock waves on the airfoil were clearly captured. A spectral analysis showed that the fundamental frequency of shock-wave oscillation agreed very well with that calculated based on the mechanism proposed by Lee. These results show that the selected PC-PSP can offer a powerful means to study transonic buffeting on airfoils and 3D wings.