Design and characterization of a multifunctional low-speed anechoic wind tunnel at HKUST

Yi, Wei; Zhou, Peng; Fang, Yi; Guo, Jingwen; Zhong, Siyang; Zhang, Xin; Huang, Xun; Zhou, Guocheng; Bao, Changchun

doi:10.1016/j.ast.2021.106814

Cited by 35 publications

(6 citation statements)

References 50 publications

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“…First, we will verify the implementation of the noise computation model by comparing results with experimental measurements in an anechoic chamber (Yi et al 2021;Wu et al 2020). The two-bladed rotors APC 9 × 5 (with the tip radius of r tip = 11.43 cm) and APC 11 × 5 (with the tip radius of r tip = 13.97 cm) are investigated.…”

Section: Verification Of the Noise Computation Model Implementationmentioning

confidence: 99%

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An investigation of rotor aeroacoustics with unsteady motions and uncertainty factors

et al. 2023

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The aeroacoustic characteristics of flying vehicles with pitch-fixed rotors differ from traditional helicopters with pitch-controlled rotor blades. Accurate predictions of rotor noise are still challenging because many uncertainty factors and unsteadinesses exist. This work investigates the aeroacoustic effects of rotational speed deviation, rotation speed fluctuation, blade vibration and blade geometric asymmetry. The analysis is based on the efficient computation of rotor noise under different working conditions. The mean aerodynamic variables are computed using the blade element moment theory, while small-amplitude fluctuations are introduced to account for the unsteadiness and uncertainty factors. It is shown that periodic rotation speed fluctuations and blade vibrations can produce significant extra tones. By contrast, if the fluctuations and vibrations are random, the noise level in a wide frequency range is increased. The intriguing result reminds us of the need to revisit the rotor broadband noise sources commonly attributed to turbulent flows. The influences are observer angle dependent, and the extra noise production is more significant in the upstream and downstream directions. The asymmetric blade geometry can cause extra tonal noise at the harmonics of the blade shaft frequency. The noise features of dual rotors are also investigated. Usually, the noise is sensitive to the initial phase difference and rotation directions due to the interference effect. However, the noise features are vastly altered if there are slight differences in the rotation speeds. Although the influences of some factors on rotor noise were already known, the present study provides a more comprehensive analysis of the problem. The results also highlight the need to consider these practical factors for accurate noise prediction of multi-rotor flying vehicles.

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Section: Verification Of the Noise Computation Model Implementationmentioning

confidence: 99%

“…First, we will verify the implementation of the noise computation model by comparing results with experimental measurements in an anechoic chamber (Yi et al. 2021; Wu et al. 2020).…”

Section: Influences On the Aeroacoustics Of An Isolated Rotormentioning

confidence: 99%

An investigation of rotor aeroacoustics with unsteady motions and uncertainty factors

et al. 2023

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“…In figure 5, table 1, an overview of typical examples across several institutions and industrial players in the world is presented (t.b.n. sources from institutional websites, copyrights infos are added together with the manuscript) with re-design strategies that have brought the originally aerodynamic facilities to reach background noise levels as low as 40 dB [24,[48][49][50][51][52]. From the experience of the scientific community, while acoustic absorbing materials are installed on the wall of the confinement regions for lowering the background noise constituted by wave reflections, acoustically transparent materials instead are typically employed in wind-tunnel walls to reduce the hydrodynamic interference of the wall-bounded flow on the recessed microphones, which can be safely installed at a distance behind them.…”

Section: Anechoic Refurbishments and Acoustic Transparent Wallsmentioning

confidence: 99%

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

Ragni¹,

Avallone²,

Casalino³

2022

Meas. Sci. Technol.

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Sustainability has encouraged studies focusing on lowering the aeroacoustic impact of new aerodynamically optimized mechanical systems for several applications in wind energy, aviation, automotive and urban air mobility. The deployment of effective noise reduction strategies start with a deep understanding of the underlying mechanisms of noise generation. To elucidate the physics behind the formation of aerodynamic sources of sound, experimental techniques used for aerodynamic purposes have been combined with acoustic measurements. In the last decades, new experimental post processing techniques have additionally been developed, by leveraging aeroacoustic analogies in a new multi disciplinary framework. New approaches have been developed with the intent of translating near field velocity and pressure information into sound. The current review describes how such breakthroughs have been achieved, briefly starting from an historical overview, to quickly bridge to the measurement techniques and the facilities employed by the scientific community. Being the measurement principles already reported in literature, this review only focuses on the most relevant studies trying to relate near field information to the perceived sound in the far field. Aspects related to the uncertainty of the measurement techniques will be thus very briefly discussed, together with their relation to the background noise of the testing facilities, including acoustic reflections/refractions, and issues due to installation of the instrumentation.

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“…The experiments were conducted in an open-jet wind tunnel Ultra-quiet Noise Injection Test and Evaluation Device (UNITED) at HKUST 12 . The test section is enclosed by an anechoic chamber with a cut-off frequency of around 200 Hz.…”

Section: A Wind Tunnel Flat Plate and Obstaclesmentioning

confidence: 99%

“…The nozzle exit has a dimension of 0.4 m (L) × 0.4 m (W ). The wind tunnel can generate incoming flows up to 60 m/s with a turbulence intensity less than 0.25% 12 . The experimental setup is sketched in Fig.…”

Section: A Wind Tunnel Flat Plate and Obstaclesmentioning

confidence: 99%

An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

Sundeep

Zhou

et al. 2022

Physics of Fluids

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This paper reports an experimental study on the aerodynamic noise generated by a two-dimensional large obstacle in a turbulent boundary layer. Square and triangular obstacles with varying heights of h/δ=0.48,0.8,1.2,1.6, and 2 (where δ is the boundary layer thickness measured without the obstacle present) are tested at various flow speeds ranging from 20 to 50 m/s. The Reynolds number based on step height and free stream velocity ranged between 7500 and 79 000. A linear microphone array is arranged aside to measure the sound radiation in the spanwise direction. It is suggested that both square and triangular obstructions can lead to a broadband source with a dipole-type directivity. A consistent increase in the noise strength is observed with obstacle height and flow speed. The underlying noise source is revealed by comparing the acoustic spectra of different obstacle geometries. The low-frequency noise is contributed by the turbulence modification due to the flow impingement onto the obstacle, while the high-frequency sound is mainly caused by the diffraction of hydrodynamic pressure by the sharp leading edge.

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Design and characterization of a multifunctional low-speed anechoic wind tunnel at HKUST

Cited by 35 publications

References 50 publications

An investigation of rotor aeroacoustics with unsteady motions and uncertainty factors

An investigation of rotor aeroacoustics with unsteady motions and uncertainty factors

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

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