Aerodynamics And Aeroacoustic Response Of Low-Reynolds Number Propellers With Unequal Blade Spacing

Abstract

This study investigates the aerodynamic and aeroacoustic performance of a two-bladed, radially asymmetric propeller featuring 90-degree blade spacing under static flight conditions. This configuration was used to isolate the effect of blade spacing. Results were compared against a symmetric, reference propeller with equivalent blade geometry and similarity parameters. Performance tests showed aerodynamic efficiency parity, despite a slight reduction in both thrust and torque. Free-field acoustic measurements revealed a redistribution of tonal energy, with dominant tones shifting from the blade-passing frequency (BPF) to 0.5BPF. This shift moved acoustic energy into the frequency range with greater attenuation under A-weighting, resulting in reduced perceived loudness. While broadband noise was reduced in the mid-frequency domain, an increase was observed above 10 kHz. The results suggest that uneven blade spacing offers a perceptually effective noise mitigation strategy for UAS applications.