Acoustic comparison of propellers

This paper presents the results of computational fluid dynamics for flows around the propellers and compares their aerodynamic performance as well as their acoustics. After some validation of the employed computational fluid dynamics method, using wind tunnel experiments, a modern propeller design was assessed. Using the same baseline blade, different propellers were put together by adding stagger at the blade hub and small variations of the inter-blade angle. The employed method produced results showing differences in the propeller acoustics regarding the frequency spectrum produced by each design and the level of the acoustic tones. The effect of changing the hub was to generate frequencies in-between the tones of the baseline design while keeping the overall propeller performance the same. The effect of the employed hub changes was to generate tones in-between the harmonics of the fundamental blade passing frequency that dominated the baseline design. Installed and un-installed blades were compared and the results show that the wing, nacelle and fuselage around the blades influence the obtained level of noise but not the frequency content. Computations for a climbing case also show the strong effect of the flight conditions on the acoustic results.