Experimental validation of unsteady pressure-sensitive paint for acoustic applications

Fast response Pressure-Sensitive Paint (iPSP) developed at the German Aerospace Center (DLR) in Göttingen is evaluated for measurements of acoustic pressure distributions. A test facility is constructed, which allows to measure these acoustic pressure distributions with iPSP. The aim of this evaluation is to detect pressure amplitudes below 100 Pa with sinusoidal and white noise acoustic excitation between 1 and 4 kHz. The following data analysis methods are applied to increase the signal-to-noise ratio (SNR): phase averaging, proper orthogonal decomposition (POD), dynamic mode decomposition (DMD), and fast Fourier transform (FFT). DMD is identified to be very powerful in extracting acoustic pressure fluctuations and eliminating image noise, but FFT achieves comparable results in this application. The used measurement setup combined with the DMD or FFT are capable of detecting pressure levels below 11 Pa or 114 dB sound pressure level (SPL) in cases with white noise excitation with detected mode frequencies up to 4615 Hz. The minimal detectable pressure limit during this investigation is 5 Pa or 108 dB (SPL) at 1318 Hz and sinusoidal acoustic excitation. The results from iPSP are compared to conventional measurement technique, flush with the surface mounted microphones, with good agreement.