Experimental noise characterisation of different pitch propellers in forward flight

The present study investigates the influence of blade pitch on propellers' aerodynamic load and noise characteristics during forward flight operations. A series of experiments have been carried out on an isolated propeller configuration in the aeroacoustics facility at the University of Bristol. Thrust, torque and far-field noise are measured at varying inflow speeds. Acoustic spectral and directivity analyses are performed to understand the distribution of acoustic radiations with frequency and emission angles, respectively. The results are presented in propeller loading variation, power spectral density of acoustic pressures, and overall sound pressure level directivity. The results reveal that under matching operating conditions, the acoustic spectral and directivity of lower-pitched propellers are strongly characterised by the high-frequency broadband noise contributions. In contrast, higher-pitched propellers are significantly influenced by the low-frequency tonal noise contributions for both spectrum and directivity features.