Measurement Technique for Unsteady Low-Speed Flow Fields Using Poly(TMSP)-Based Pressure Sensitive Paint

Nonstationary analysis of flow field is required to detect the source of aerodynamic noise, in order to accomplish the reduction of aerodynamic noise in life environment, including low-frequency noise, which may be harmful for human health. Pressure sensitive paint (PSP) is a quantitative pressure visualization technique on solid surfaces based on oxygen quenching of luminescent molecule. Polymer-type PSP composed of PtTFPP, a luminescent molecule with high oxygen quenching probability, and poly(TMSP), a glassy polymer with high oxygen permeability, has high pressure sensitivity for low-speed flow field. However, the pressure sensitivity of the polymer-type PSP for nonstationary pressure change has not been examined enough. In this study, we investigate the time response of the poly(TMSP)-based PSP, to evaluate the feasibility of the polymer-type PSP as a measurement tool for nonstationary low-speed flows, when the frequency of pressure fluctuation is relatively low. Because response time of polymer-type PSP is proportional to the square of the thickness of the PSP layer, we prepare thinner-layer PSP to increase the response speed by reducing the amount of polymer. The polymer-type PSP is applied to measurement of nonstationary pressure distribution around a circular cylinder in low-speed flow, and compare the amplitude spectra of PSP and that of pressure probe, which are obtained by FFT analysis. As a result it is clarified that the sensitivity of the PSP for pressure variation lower than 100Hz is as high as that for stationary pressure. For pressure variation higher than 100Hz the sensitivity decreases as the frequency of pressure variation increases, but pressure variation with the amplitude of about 300Pa can be detected by the poly(TMSP)-based PSP even if the frequency is as high as 850Hz. Furthermore we have visualized the distribution of the integrated intensity of the PSP amplitude spectrum around the peak, to visualize the area with large pressure variation on the cylinder surface.