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20.06 UAVs and the Future of Urban Soundscape

Experimental investigation on acoustics and efficiency of rotor configurations for electric aerial vehicles
Time: 8:00 am

Author: Ronja König

Abstract ID: 1435

Aerial vehicles based on distributed electric propulsion systems have gained great interest. Their rotors however create loud and annoying sound, what obstructs market success. Variations in rotor configuration can be observed on emerging concepts, whereby the main varied parameters are blade radius, number of blades and blade distribution. The focus of this paper is to identify how these parameters can be chosen to optimize efficiency and acoustics, including psychoacoustic metrics and sound quality of single rotors while hovering. Results from experimental investigations done in a hover-test-bench are presented. Rectangular, symmetric blades are used. Experiments are done varying blade radius (61mm to 126 mm), number of blades (2 to 8) and blade distribution (equal and unequal angles). Acoustic measurements are analyzed regarding microphone position, sound pressure level, spectral characteristics, psychoacoustic metrics and selected sound quality models. Results show, that variations in blade radius, number of blades and blade distribution can improve efficiency and acoustics. Influence of these parameters on the acoustic signature at constant rotational speed and at constant thrust is discussed. Conclusions for optimized rotor design at aerial vehicles are derived and supplemented by resulting boundary conditions like building space and weight.

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Community noise from a drone delivery distribution center: challenges and options
Time: 2:40 pm

Author: Jacob Poling

Abstract ID: 1652

As drone package delivery services are expanded, community noise will be an issue that every operator will need to consider. Drones represent a unique new community noise source that will operate and be perceived differently than traditional aircraft and ground transportation vehicles. It is also likely that some early implementations of drone delivery services by major retailers will operate out of existing distribution centers, which may not be ideally located from a noise perspective. This study considers potential drone delivery noise in the community surrounding an existing distribution center, assuming the facility were to be utilized as the hub of a future drone package delivery service. The predicted noise levels from drone deliveries are compared to typical community noise limits, and potential alternative noise metrics for assessing annoyance from drone noise in communities are discussed. Options to reduce community noise from drone deliveries by altering flight altitude and speed, utilizing different flight path routing strategies, and taking advantage of the potential masking of drones by existing roadway noise are considered.

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Sound, noise, annoyance? Information as a means to strengthen the public acceptance of civil drones
Time: 7:20 am

Author: Hinnerk Eissfeldt

Abstract ID: 2045

Civil drones are becoming ever more present in public perception. Ranging from parcel delivery to wildlife protection and from precision farming to law enforcement, many applications are said to have market-changing potential. Against this background, nations and institutions around the world are trying to keep up with the dynamic technological developments by means of rules and regulations. Since all parties involved expect a strong increase in both the number of drones and the range of their uses, there is a rising interest in the public acceptance of these vehicles. Widespread acceptance can promote the dissemination of new technologies. Conversely, citizens’ concerns about the use of drones in their daily environment may pose barriers to the further proliferation of civil drones, especially in urban areas. The psychoacoustic properties of the vehicles have repeatedly been discussed as being one such limiting factor. This paper discusses results of a representative national study on the social acceptance of civil drones, taking a closer look at effects of information about drones as potential means to foster public acceptance. The findings underline the role of well planned information campaigns as well as community engagement in managing the contribution of drones in future urban soundscapes.

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Visual and audio perception study on drone aircraft and similar sounds in an Urban Air Mobility setting
Time: 7:00 am

Author: Roalt Aalmoes

Abstract ID: 2160

Urban Air Mobility (UAM) is a novel aerospace concept involving drones and Personal Air Vehicles (PAVs) operating in a densely populated urban environment. Most of such vehicles will be electric-powered and rotor-based, creating a distinct sound in the proposed setting of a city. Public acceptability, partially due to noise impact, is a valid concern for the introduction of UAM. To evaluate human perception and noise annoyance of these vehicles, a study is set up that comprises audio-only and combined audio-visual stimuli of hovering and fly-over events using a Virtual Reality experiment. For both types of stimuli, two ambient environments, recorded with synchronized spherical video and ambisonics audio, are provided as background: a louder urban street environment, and a quieter urban street environment. In addition to the drone sounds, more familiar sounds are also evaluated, namely a helicopter and a lawnmower sound, with and without a visualisation. Test subjects are asked about their noise sensitivity according to a shortened Weinstein scale, and their attitude towards drones using a separate questionnaire at the end of the experiment. [Note from authors: The laboratory study is ongoing and the first results are being analysed. The final results are expected well before the paper deadline. This abstract will be complemented with the main results and conclusions.]

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Perception of noise from small quadcopter UAVs
Time: 6:20 am

Author: Michael Kingan

Abstract ID: 2256

This paper presents the results of a study evaluating the human perception of the noise produced by small quadcopter UAVs. The study utilised recordings of the noise produced by several different quadcopter UAVs in hover and in constant-speed flight at a fixed altitude. These recordings were made using an eigenmic system. The recordings were reproduced using a 3D sound reproduction system located in the large anechoic chamber at the University of Auckland. Human subjects were asked to rate the annoyance of the recordings. The responses of the test subjects are presented and these are compared with objective metrics to assess suitable metrics for quantifying the impact of noise from these vehicles on humans.

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Performance evaluation on multi-channel Wiener filter based speech enhancement for unmanned aerial vehicles recordings
Time: 6:40 am

Author: Yusuke Hioka

Abstract ID: 2457

Recording speech from unmanned aerial vehicles has been attracting interest due to its broad application including filming, search and rescue, and surveillance. One of the challenges in this problem is the quality of the speech recorded due to contamination by various interfering noise. In particular, noise contamination due to those radiated by the unmanned aerial vehicles rotors significantly impacts the overall quality of the audio recordings. Multi-channel Wiener filter has been a commonly used technique for speech enhancement because of its robustness under practical setup. Existing studies have also utilised such techniques in speech enhancement for unmanned aerial vehicle recordings, such as the well-known beamformer with postfiltering framework. However, many variants of the multi-channel Wiener filter have also been developed over recent years such as the speech distortion weighted multi-channel Wiener filter. To address these recent advancements, in this study we compare the performance of these variants of techniques. In particular, we explore the benefits these techniques may bring forth in the setting of audio recordings from an unmanned aerial vehicle.

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A Hybrid and Efficient Low-noise assessment Platform for Urban aerial mobility (HELPU)
Time: 6:00 am

Author: Siyang Zhong

Abstract ID: 2509

Urban aerial mobility (UAM) is a promising approach to improve the traffic situation in gigantic cities, which, however, may encounter significant noise pollution issues. An integrated research platform, which is being established at HKUST, to include noise generation, long-distance propagation, and perception at the observers is timely to assess the environmental impact of UAM noise and to develop low-noise designs and flight planning. A high-quality test rig in the anechoic aerodynamic facility at HKUST is employed to measure the propeller aeroacoustics and aerodynamics, and to enable the innovative noise control device and design studies. The measurements and high-fidelity simulations using an in-house computational aeroacoustics solver can lead to comprehensive databases to facilitate and validate the development of physics-oriented noise prediction models. Also, high-efficient implementation of the boundary element method is conducted to account for the noise scattering due to the fuselage and then to evaluate the impact of UAM layout on the directivity patterns, which will then be efficiently projected to the far-field observers using the advanced Gaussian beam tracing with the effects due to moving source, atmospheric attenuation, and refraction, complex boundary absorption and reflection incorporated. Low-noise flight planning is then be made accordingly.

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The multi-functional rotor aerodynamic and aeroacoustic test platform at HKUST
Time: 8:20 am

Author: Han Wu

Abstract ID: 2695

This paper describes the multi-functional rotor noise and aerodynamics test platform at the Hong Kong University of Science and Technology (HKUST). To investigate the noise characteristics of propellers with aerodynamic flows, the test rig is installed in the 2.5×2 (m) low-speed and low-noise wind tunnel in the Aerodynamic and Acoustic Facility (AAF) at HKUST. The wind tunnel can facilitate flow from 0 to 40 m/s. The test rig is assembled in a turntable on the ceiling of the tunnel wall, which enables the testing range of pitch angle can vary from 0° (axial flow) to 90° (parallel flow), with an accuracy of 0.1°. The noise produced by the rotor is measured by a set of wall-mounted surface microphones. Semi-empirical calibration is conducted to quantify the noise reflection by the tunnel walls. A low-noise struct has been designed and manufactured to locate a set of far-field microphones equipped with nosecone, to improve the quality of acoustic measurement inside the flow. In addition, a synchronized system is developed to conduct the phase-locking Particle Image Velocimetry (PIV) measurement on the rotor, to study the flow pattern to better understand the noise generation mechanism.

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Experimental assessment of the noise characteristics of propellers for commercial drones
Time: 8:40 am

Author: Han Wu

Abstract ID: 2697

Multi-copters or drones are engaged in a wide range of industrial applications for their flexibility, safety and low-cost. The noise emission is becoming an issue with the expanding applications, among which the propellers that drive the drones are the major sources of noise. In this work, the noise characteristics of small-scale propellers is experimentally investigated using the advanced rotor aerodynamics and aeroacoustics test platform in an anechoic chamber at the Hong Kong University of Science and Technology (HKUST). The study will focus on the representative off-the-shelf propellers. The rotor noise will be measured by a linear array with 20 microphones, and the aerodynamic forces will be acquired by using the high-accuracy load cells. The dependence of both the tonal and broadband noise radiation with the thrust and rotation speed at various conditions will be tested. The study will enhance our understanding of the noise features of the multi-rotor powered drones, and will provide us with a better understanding of the status of the drone noise impact on the environment.

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