15:30
Experimental Aeroacoustic Measurements – Field 2
15:30
20 mins
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Effect of Propeller Blade Spacing on Quadcopter’s Aeroacoustic Noise and Sound Quality
Carlos Ramos-Romero, Dima Usov, Antonio Filippone, Antonio Torija Martinez
Abstract: Previous studies have demonstrated that propeller and blade geometry are primary contributors of aeroacoustic noise in propeller‑driven vehicles. This raises the question: how does the noise signature of an Unmanned Aircraft System (UAS) equipped with two aerodynamically similar, but geometrically different propeller set change? To investigate this, an outdoor measurement campaign was conducted to characterise the acoustic response of the vehicle operating with two aerodynamically equivalent, two-bladed, low-Reynolds-number propeller sets with different blade spacing angles.
The acoustic energy distribution across the frequency spectrum induced by propeller geometry is examined for three distinct flight operations: take-off, hovering, and landing. These operations were characterised using a set of acoustic descriptors ( LAmax, LAeq and LAE). By keeping operational conditions (e.g., altitude and speed) and design parameters (e.g., number of blades and motors, and vehicle mass) constant, significant differences in the emitted noise were observed as a function of propeller blade-spacing angle.
A shift of acoustic energy toward the low-frequency range and a redistribution of high harmonics were observed when the vehicle operated with the altered blade-spacing-angle propeller compared with the baseline propeller configuration. This spectral modification affected the evaluated sound quality metrics (e.g., loudness, sharpness and tonality). Variations exceeding the just noticeable difference thresholds in the sound quality metrics indicate that modifying propeller design can plausibly alter perceived noise while maintaining aerodynamic performance.
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15:50
20 mins
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Influence of acoustic ground reflections on the sound perception of a hovering quadcopter drone
Roberto Merino-Martinez, Renatto Yupa Villanueva, Josephine Pockelé, Amy Morin, Mirjam Snellen
Abstract: The rapid growth in the use of unmanned aerial vehicles (UAVs), commonly referred to as drones, over the past decades has raised increasing concerns regarding their noise emissions, which constitute a major barrier to their widespread societal acceptance. As a result, substantial research efforts have been devoted to characterizing and analyzing the acoustic emissions of these devices. From an experimental perspective, a large proportion of drone noise measurements are typically conducted under anechoic laboratory conditions, corresponding to free-field sound propagation (i.e. without significant reflections). Such measurements often serve as the basis for noise modelling and auralization tools.
In realistic outdoor operational environments, however, sound reflections from the ground and surrounding surfaces (e.g. buildings) inevitably occur, altering the acoustic signal received by an observer. Although these reflection effects can be modelled analytically to some extent within auralization frameworks, their influence on the perceptual attributes of drone noise remains insufficiently understood.
To address this gap, acoustic measurements were conducted in the anechoic chamber of the Faculty of Applied Sciences at Delft University of Technology using a DJI Mavic 3 Enterprise quadcopter. Two experimental configurations were considered: a fully anechoic setup (without floor) and a hemi-anechoic setup (with a solid wooden floor). Recordings were performed using three vertical 16-microphone arrays positioned at three different azimuthal emission angles relative to the drone. Measurements were obtained at two hover heights, 1 m and 2 m, thereby covering a broad range of emission angles (see Fig. 1).
The recorded signals will be analyzed using psychoacoustic sound quality metrics, including loudness, sharpness, tonality, roughness, and fluctuation strength, computed with the open-access Sound Quality Analysis Toolbox (SQAT) and a small-scale listening experiment. Differences between the fully anechoic and hemi-anechoic configurations will be evaluated in relation to the corresponding just-noticeable differences (JNDs) per SQM, providing insight into the perceptual relevance of ground reflections on drone noise. Lastly, comparisons with well-known ground reflection models (e.g. Delany & Bazley) will be made.
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16:10
20 mins
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Modelling the sound exposure for a field study on medical UAV operations in the city of Zurich, Switzerland
Claudio Affolter, Jonas Meister, Jean Marc Wunderli
Abstract: Unmanned Aerial Vehicles (UAVs) are an emerging source of environmental noise due to their rapidly growing use in a wide range of civil applications. While authorities are required to assess the noise of such drone operations, clear legal frameworks are still largely lacking. Developing regulations requires scientific evidence on public acceptance and human response to drone noise. However, to date, field studies on the effects of noise by UAV operations on the population are still missing. In this contribution, we present the development of a drone noise emission model and subsequent simulation of the sound exposure in residential areas around flight paths of real-world UAV operations in the city of Zurich, Switzerland. Over a six-month period in 2025, UAVs were used for medical transport purposes (medication and laboratory samples) between hospitals within the city. The acoustic emission model was obtained from a measurement campaign of different flight maneuvers, using a microphone setup covering a wide range of emission angles. The measurements, combined with recorded flight data, were used to develop a regression-based emission model of the UAV’s sound power level. Model verification revealed that on average, the model overestimates the sound exposure level by 0.2 dB and the maximum sound pressure level by 0.6 dB. In a next step, the emission model was used to simulate the sound exposure along the flight paths, and the results were compared with recordings from noise monitoring stations along these routes for validation purposes. The simulations at residents’ homes will be used for noise impact assessment and linked with the results of a field survey on perception of and annoyance to noise of UAV operations.
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