Unsteady PSP Technique for Measuring Naturally-Disturbed Periodic Phenomena

To understand unsteady flow phenomena, it is important to measure time-resolved pressure variations with high spatial resolution. Pressure Sensitive Paint (PSP) has a capability of providing high-resolution pressure images, but the Signal-to-Noise Ratio (SNR) is not high enough to analyze unsteady flow structures in low-speed flow. The phase-lock method is often applied to PSP measurement of periodic flow phenomena, but it is difficult to apply this technique to unsteady flow containing natural disturbances in amplitude and phase. To solve this problem, we propose a new type of phase-lock method in which images of unsteady pressure field are phase-locked using a trigger signal processed with signal conditioning techniques such as band-pass filtering and signal differentiation. The effectiveness of this method was verified using simulated signal and applied to low-speed wind tunnel testing of a 3-D square cylinder model. As a result, we could obtain time-resolved unsteady pressure field on the side of the square cylinder due to periodic Karman vortex shedding. The fluctuating pressures were found to be high at the lower part of the side wall, that is in good agreement with the pressure transducers data.

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