Effects of flow recirculation on acoustic and dynamic measurements of rotary-wing systems operating in closed anechoic chambers

Weitsman, Daniel; Stephenson, James H.; Zawodny, Nikolas S.

doi:10.1121/10.0001901

Cited by 31 publications

(4 citation statements)

References 10 publications

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“…Turbulent inflow noise can be predicted using a computational method such as that described in [21] or analytical methods such as that described by [22]. Note that tests conducted in anechoic chambers or confined spaces will produce a recirculating flow, which can produce high levels of turbulent inflow noise [23,24]; •…”

mentioning

confidence: 99%

Quantification of the Psychoacoustic Effect of Noise from Small Unmanned Aerial Vehicles

Hui

Kingan

Hioka

et al. 2021

IJERPH

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This paper presents the results of a study evaluating the human perception of the noise produced by four different small quadcopter unmanned aerial vehicles (UAVs). This study utilised measurements and recordings of the noise produced by the quadcopter UAVs in hover and in constant-speed flight at a fixed altitude. Measurements made using a ½″ microphone were used to calculate a range of different noise metrics for each noise event. Noise recordings were also made using a spherical microphone array (an Eigenmike system). The recordings were reproduced using a 3D sound reproduction system installed in a large anechoic chamber located at The University of Auckland. Thirty-seven participants were subjected to the recordings and asked to rate their levels of annoyance in response to the noise, and asked to perform a simple cognitive task in order to assess the level of distraction caused by the noise. This study discusses the noise levels measured during the test and how the various noise metrics relate to the annoyance ratings. It was found that annoyance strongly correlates with the sound pressure level and loudness metrics, and that there is a very strong correlation between the annoyance caused by a UAV in hover and in flyby at the same height. While some significant differences between the distraction caused by the UAV noise for different cases were observed in the cognitive distraction test, the results were inconclusive. This was likely due to a ceiling effect observed in the participants’ test scores.

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mentioning

confidence: 99%

Quantification of the Psychoacoustic Effect of Noise from Small Unmanned Aerial Vehicles

Hui

Kingan

Hioka

et al. 2021

IJERPH

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“…Experimentalists studying the noise of unmanned aerial systems (UAS) take caution to ensure that noise due to recirculation of their own turbulent wake does not dominate noise measurements conducted in enclosed areas. [155][156][157] That research, along with other recent research, 158,159 suggest that ingestion noise can contribute significantly to UAS noise. Thus this is an important area for future research, which could also have some relevance for eVTOL aircraft.…”

Section: Ingestion Noisementioning

confidence: 63%

Challenges and opportunities for low noise electric aircraft

Greenwood

Brentner

Rau

et al. 2022

International Journal of Aeroacoustics

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A new class of electric aircraft is being developed to transport people and goods as a part of the urban and regional transportation infrastructure. To gain public acceptance of these operations, these aircraft need to be much quieter than conventional airplanes and helicopters. This article seeks to review and summarize the aeroacoustic research relevant to this new category of aircraft. First, a brief review of the history of electric aircraft is provided, with an emphasis on how these aircraft differ from conventional aircraft. Next, the physics of rotor noise generation are reviewed, and the noise sources most likely to be of concern for electric aircraft are highlighted. These are divided into deterministic and nondeterministic sources of noise. Deterministic noise is expected to be dominated by the unsteady loading noise caused by the aerodynamic interactions between components. Nondeterministic noise will be generated by the interaction of the rotor or propeller blades with turbulence from ingested wakes, the atmosphere, and self-generated in the boundary layer. The literature for these noise sources is reviewed with a focus on applicability to electric aircraft. Challenges faced by the aeroacoustician in understanding the noise generation of electric aircraft are then identified, as well as the new opportunities for the prediction and reduction of electric aircraft noise that may be enabled by advances in computational aeroacoustics, flight simulation, and autonomy.

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“…The experiment was conducted inside an enclosure of m that confines the helium-filled soap bubbles (HFSB) used as flow tracers (Faleiros, Tuinstra, Sciacchitano, & Scarano, 2019). Any effects of re-circulation in the enclosure are observed at frequencies comparable to the BPF (Weitsman, Stephenson, & Zawodny, 2020) and therefore do not affect the relatively large time scales of interest. Five HFSB generators delivered roughly 150 000 bubbles per second, which were nearly neutrally buoyant and had a mean diameter of 0.4 mm.…”

Section: Experimental Apparatus and Proceduresmentioning

confidence: 99%

Unsteady flow behaviour of multi-rotors in ground proximity

Dekker,

Baars,

Scarano

et al. 2023

Flow

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The unsteady flow behaviour of two side-by-side rotors in ground proximity is experimentally investigated. The rotors induce a velocity distribution interacting with the ground causing the radial expansion of the rotor wakes. In between the rotors, an interaction of the two wakes takes place, resulting in an upward flow similar to a fountain. Two types of flow topologies are examined and correspond to two different stand-off heights between the rotors and the ground: the first one where the height of the fountain remains below the rotor disks, and a second one where it emerges above, being re-ingested. The fountain unsteadiness is shown to increase when re-ingestion takes place, determining a location switch from one rotor disk to the other, multiple times during acquisition. Consequently, variable inflow conditions are imposed on each of the two rotors. The fountain dynamics is observed at a frequency that is about two orders of magnitude lower than the blade passing frequency. The dominant characteristic time scale is linked to the flow recirculation path, relating this to system parameters of thrust and ground stand-off height. The flow field is analysed using proper orthogonal decomposition, in which coupled modes are identified. Results from the modal analysis are used to formulate a simple dynamic flow model of the re-ingestion switching cycle.

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Effects of flow recirculation on acoustic and dynamic measurements of rotary-wing systems operating in closed anechoic chambers

Cited by 31 publications

References 10 publications

Quantification of the Psychoacoustic Effect of Noise from Small Unmanned Aerial Vehicles

Quantification of the Psychoacoustic Effect of Noise from Small Unmanned Aerial Vehicles

Challenges and opportunities for low noise electric aircraft

Unsteady flow behaviour of multi-rotors in ground proximity

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