Near-field measurements of stationary and rotating in-duct sound sources with pressure-sensitive paint

Pressure Sensitive Paint (PSP) was applied on a disc, which was situated in a short duct with a diameter of 500 mm. The disc featured an acoustic source, a flush mounted loudspeaker, to investigate its acoustic near-field with high spatial resolution. Experiments were conducted with the disc in stationary and rotating mode. Three different source frequencies were investigated with 2 kHz, 3 kHz and 4 kHz for both stationary and rotating cases. The unsteady near-field of the source was analyzed in terms of spatially averaged spectra. The results of the unsteady near-field measured with pressure sensitive paint are verified by comparison with azimuthal mode spectra from a microphone ring array mounted flush at the outer duct wall and close to the disc. The results provide a sufficient signal-to-noise ratio and a very high spatial resolution of the unsteady pressure field.