Growing interest in efficient short-haul and electric regional aviation has renewed focus on propeller-driven aircraft, although open rotors pose significant noise challenges. This study investigates how noise perception—quantified by the Effective Perceived Noise Level (EPNL)—in
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Growing interest in efficient short-haul and electric regional aviation has renewed focus on propeller-driven aircraft, although open rotors pose significant noise challenges. This study investigates how noise perception—quantified by the Effective Perceived Noise Level (EPNL)—influences propeller blade design, with particular attention to blade sweep. Aerodynamic modelling is carried out using a Vortex Lattice Method, while aeroacoustic analysis relies on Hanson’s frequency-domain tonal noise model.
A parameter study reveals that perceived noise plays a more critical role during take-off than cruise in guiding propeller design, and that blade sweep is more effective at reducing perceived noise than physical noise, especially at high rotational velocities.
In the second part of the study, multiple trade-off analyses are conducted through a series of optimisations that minimise EPNL under progressively loosened power requirements, all performed under take-off conditions. The results indicate that while reducing rotational velocity remains the most effective strategy for lowering both physical and perceived noise, the fundamental frequency becomes increasingly dominant in the total tonal noise. Consequently, optimisation for perceived rather than physical noise results in similar blade geometries, but with progressively greater reductions in perceived noise relative to physical noise because of the lowering Blade Passage Frequency, which the human ear is less sensitive to. Among various sweep-induced noise reduction mechanisms, fixing the blade radius—rather than the blade length—yields greater noise reduction, primarily due to reduced blade loading as the blade lengthens with introduced sweep.
A comparison of EPNL-optimised designs requiring 1% additional power shows that allowing the blade length to vary under a fixed radius enables a further 7.2 dB reduction in perceived noise. When examining the effectiveness of sweep versus twist under constant blade radius conditions, and again allowing 1% extra required power, blade twist achieves a 1.3 dB reduction in perceived noise, while blade sweep provides an additional 4.6 dB reduction.
