Aerodynamic and Aeroacoustic Performance of Small UAV Propellers in Static Conditions

Abstract

The proliferation of small multi-rotor UAVs in commercial, recreational, and surveillance spheres has garnered significant interest in the noise produced by these vehicles. The current research aims to study the relationship between the aerodynamic performance and acoustic characteristics of small-scale UAV propellers. Three commercially available propellers for the DJI Phantom 2/3 UAV were selected for preliminary development and validation of an aeroacoustic experimental test setup and associated data reduction methods. Propeller thrust, torque, and power measurements were recorded at static conditions. Upon successful validation of the test bench, acoustic measurements were taken at the propeller disk's upstream and in-plane locations. The power spectral density of these acoustic signals was estimated using the modified periodogram (Welch's) method to identify frequency content and calculate sound pressure levels (SPLs) at each of the observation locations. Additionally, time-frequency analysis verified the periodogram results and identified possible sources of transient noise at static thrust. These methods found the nonrotor noise to be a major contributor to the SPL at higher frequencies and the propeller noise dominating the SPL spectra at the lower frequencies. Experimental thrust, torque, power, and sound pressure level (SPL) data were then compared for each propeller to identify relationships between aerodynamic performance and acoustic characteristics with variations in propeller geometry and blade loading.

Aeroacoustics Effects Generated by the Interaction Rotor-Airframe in a sUAS

“…While many studies address the case of hovering flight, the work of Caprace et al (2022) focused on analyzing the effects of rotor-airframe interaction in forward flight by performing large eddy simulation (LES). The results were relevant to show how modern techniques could be used to assess flow field data such as vortex interactions with obstacles for wake characterization purposes as also seen in other works (Jordan et al 2020;Kekus-Kumor and Sieradzki 2023;Whelchel and Alexander 2021).…”

Recent Advances in Passive Acoustic Localization Methods via Aircraft and Wake Vortex Aeroacoustics

“…Propeller noise, given its distinctive tonal features, is increasingly relevant to drone acoustic detection [66]. The acoustic characteristics of these drones are actively being investigated by a number of groups, for example [67,68]. Given the generally lower Reynolds numbers of drones compared to traditional aircraft, additional issues may arise due to laminar separation, asymmetric wake formation [69], or transitional wakes [70,71], although the impacts on the aeroacoustic noise are not fully understood.…”

Quantifying modulation in the acoustic field of a small-scale rotor using bispectral analysis

“…There is however a growing awareness that time-varying properties of the noise (an amplitude modulation), and its impulsiveness/sharpness are highly relevant for the level of annoyance; [2][3][4][5][6][7] this is in line with the conclusions made in the community of psycho-acoustics. 8 Most studies on acoustic aspects of small-scale rotors consider standard characterization schemes that rely on time/ensemble-averaging: [9][10][11][12][13][14][15][16] acoustic results are condensed to a set of acoustic spectra, their integrated energy (overall sound pressure level), as well as the directivity patterns of that (frequencydependent) energy. Occasionally, studies do employ time-preserving schemes (wavelet transforms yielding time-frequency spectra), as those are required when dealing with non-stationary acoustic signals of flyovers and maneuvering systems.…”