Acoustic Analysis of Uneven Blade Spacing and Toroidal Geometry for Reducing Propeller Annoyance

TL;DR

The paper addresses the problem of psychoacoustic annoyance from UAV propellers in populated areas by evaluating unconventional propeller geometries—toroidal and uneven blade spacing—using CFD for thrust prediction and controlled acoustic testing with an A-weighted PSD analysis. Five 6-inch, 3D-printed designs (A–E) are compared, with Type B (3-loop toroidal) delivering thrust comparable to conventional designs while exhibiting the lowest high-frequency peaks and the smallest A-weighted PSD; Type E offers additional, though smaller, reductions, and Type C underperforms due to counterweight vortices. The results suggest that a combined toroidal-uneven spacing approach can reduce both tonal and broadband noise without sacrificing thrust, offering practical routes toward quieter civil UAVs. The study advocates future work on a calculable spacing method to minimize high-frequency noise and validation under realistic flight conditions.

Abstract

Unmanned aerial vehicles (UAVs) are becoming more commonly used in populated areas, raising concerns about noise pollution generated from their propellers. This study investigates the acoustic performance of unconventional propeller designs, specifically toroidal and uneven-blade spaced propellers, for their potential in reducing psychoacoustic annoyance. Our experimental results show that these designs noticeably reduced acoustic characteristics associated with noise annoyance.

Figures (6)

• Figure 1: 3D models of our propeller types, three of which (b,c,e) were tested using physical prototypes.
• Figure 2: CFD simulation of surface pressure.
• Figure 3: CFD simulation of air velocity, represented volumetrically. Areas of high velocity at the ends of blades are tip vortices.
• Figure 4: Simulated thrust values by angular velocity for all propellers.
• Figure 5: A-weighted power spectral densities for Types D & B.