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1
Glover, Jennifer y Dan O'Boy. "Acoustic space filling curve metamaterials for grazing flow in Jet engine inlets". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 6 (1 de agosto de 2021): 394–406. http://dx.doi.org/10.3397/in-2021-1458.
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Acoustic metamaterials research has grown exponentially in the past 10 years driven by the advances in manufacturing and an increased understanding of damaging environment noise. 2020 was the first noise reduction target as set by Advisory Council for Aircraft Research and Innovation in Europe with a relative 50% decrease. This was missed by current Jet engine noise control technology; however, metamaterials offer an encouraging alternative. Space Filling Curves (SFC) have the potential to provide a lightweight, thin, high performance acoustic liner. SFC have a history in mathematical geometry dating back to the 1890's but are a comparatively new addition to acoustics. They are designed with a sub-wavelength curled cross-section creating a maze-like pattern which slows acoustic wave propagation through the liner enabling characteristics such as negative refraction and low frequency attenuation. This paper contains a comparison of some of the most promising SFC metamaterial acoustic liner designs, in terms of the fundamental theory of the design category and a discussion of the reflection, absorption and transmission characteristics in terms of a grazing flow conditions. Computer simulation and impedance tube based experimental testing compares the designs. The paper concludes with future application for aeroacoustics with particular focus on the engine inlet.
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Glover, Jennifer y Dan O'Boy. "Hybrid space filling curve metamaterials for transmissive flow in Jet Engine inlets". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 7 (1 de febrero de 2023): 491–502. http://dx.doi.org/10.3397/in_2022_0069.
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Acoustic metamaterials research has grown exponentially in the past 10 years driven by the advances in manufacturing and an increased understanding of damaging environment noise. 2050 was the first noise reduction target as set by Advisory Council for Aircraft Research and Innovation in Europe with a relative 65% decrease. This ambitions target will not be met by current engine noise control technology; however, metamaterials offer an encouraging alternative. Space Filling Curves (SFC) have the potential to provide a lightweight, thin, high performance acoustic liner. SFC have a history in mathematical geometry dating back to the 1890's but are a comparatively new addition to acoustics. They are designed with a sub-wavelength curled cross-section creating a maze-like pattern which slows acoustic wave propagation through the liner, enabling characteristics such as negative refraction and low frequency attenuation. This paper contains unique hybrid designs combining some of the most promising SFC metamaterial acoustic liner designs, in terms of the fundamental theory of the design category and a discussion of the reflection, absorption and transmission characteristics in terms of a grazing flow conditions. Experimental impedance tube testing compares 3D printed designs to the traditional Helmholtz resonator. The paper concludes with future application for aeroacoustics with particular focus on the engine inlet.
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Roncen, Remi, Pierre Vuillemin, Patricia Klotz, Frank Simon, Fabien Méry, Delphine Sebbane y Estelle Piot. "Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform applications". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 6 (1 de agosto de 2021): 152–63. http://dx.doi.org/10.3397/in-2021-1308.
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In the context of noise reduction in diverse applications where a shear grazing flow is present (i.e., engine nacelle, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency regime, where space constraints currently limit the efficiency of classic liner technology. To perform the required multi-objective optimization of complex meta-surface liner candidates, a software platform called OPAL was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial assembly of unit acoustic elements, including the recent concept of LEONAR materials. Then, the physical properties of this liner can be optimized, relatively to given weighted objectives (noise reduction, total size of the sample, weight), for a given configuration. Alternatively, properties such as the different impedances of liner unit surfaces can be optimized. To accelerate the process, different nested levels of optimization are considered, from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin resolution of the Linearized Euler Equations. The presentation will focus on the different aspects of liner design considered in OPAL, and present an application on different samples made for a small scale aeroacoustic bench.
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Butt, Abdul Hadi, Bilal Akbar, Jawad Aslam, Naveed Akram, Manzoore Elahi M. Soudagar, Fausto Pedro García Márquez, Md Yamin Younis y Emad Uddin. "Development of a Linear Acoustic Array for Aero-Acoustic Quantification of Camber-Bladed Vertical Axis Wind Turbine". Sensors 20, n.º 20 (21 de octubre de 2020): 5954. http://dx.doi.org/10.3390/s20205954.
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Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques.
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Shen, Zihan, Xiaoyu Wang y Xiaofeng Sun. "Noise reduction by perforated cascades in annular ducts". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 5 (1 de febrero de 2023): 2124–35. http://dx.doi.org/10.3397/in_2022_0304.
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One of the latest trends in noise control relating to aeroacoustics is to mimic the silent flight capability of owls. Particularly, porosity is most often applied on cascades in ducts with axial flows, such as stator structures in an aero-engine. However, current acoustic scattering models of perforated cascades are based on two-dimensional methods without including the three-dimensional effects. In this paper, we present a fully three-dimensional acoustic scattering model for perforated cascades based on the lifting surface theory in which the dominant sound source reduces to dipoles alone under the thin airfoil assumption. Accordingly, the acoustic scattering of perforated cascades with single-mode incident wave was studied and obvious noise reduction was observed. The optimum Rayleigh conductivity and the maximum noise-reducing capability of the porosity varied substantially with different incident duct modes, whilst a larger cascade chord-length could achieve more noise reduction at optimum porosity. With a background flow, the Kutta condition can greatly influence the overall distribution of the unsteady loading on vanes. Additionally, the unsteady vortex shedding at the trailing edge offers extra sound energy dissipation mechanism. Therefore, the implementation of porosity on cascades is much different to the design of a traditional acoustic liner.
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Kobayashi, Hiroshi, Schunichi Ozaki y Makoto Yokochi. "Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner". Advances in Acoustics and Vibration 2011 (20 de septiembre de 2011): 1–14. http://dx.doi.org/10.1155/2011/473282.
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This paper describes the development of adaptive acoustic impedance control (AAC) technologies to achieve a larger fan noise reduction, by adaptively adjusting reactance and resistance of the acoustic liner impedance. For the actual proof of the AAC technology III performance, the advanced fan noise absorption control duct liner II was made on trial basis, with the simple control system and the plain device. And, then, the duct liner II was examined for the AAC technology I, II, and III models, using the high speed fan test facility. The test results made clear that the duct liner II of the AAC technology III model could achieve the fan noise reduction higher than O.A. SPL 10 dB (A) at the maximum fan speed 6000 rpm, containing the reduction of fundamental BPF tone of 18 dB and 2nd BPF tone of 10 dB in response to the fan peed change from 3000 to 6000 rpm.
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Yan, Qun, Dongwen Xue, Qinqin Mu, Jiafeng Yang, Xiang Gao y Wenchao Huang. "Acoustic Experimental Technology for Aircraft Nacelle Liner". Aerospace 10, n.º 1 (5 de enero de 2023): 56. http://dx.doi.org/10.3390/aerospace10010056.
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An aircraft nacelle acoustic liner is a key mean of aircraft noise reduction. The success of its design depends strongly on the development of experimental technology, which is generally divided into two stages: impedance eduction and the modal verification of acoustic performance. The comparative study summarizes the impedance eduction technology based on the in-situ method and the straight forward method, and the acoustic modal measurement and control technology, as well as their applications in the design of the acoustic liner of an engine intake and exhaust ducts. The results show that the in-situ method has higher accuracy at low frequencies, and the accuracies of both methods are decreased in the high frequency range. Both methods show an acceptable accuracy and good applicability in the mid-frequency range. A modal generator was designed and used to emit separate and pure acoustic modes in sequence, and a comparative test was carried out on the two types of acoustic liner. Compared with the seamed acoustic liner, the seamless acoustic liner significantly improved its noise reduction effect at the multi-acoustic modes and target frequencies, which further increases the overall reduction up to 5.2 dB. Through research, reliable and validated technologies of acoustic performance tests for a nacelle acoustic liner were established.
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Yang, Guang Jun, Jian Jun Liu y Jing Sun. "Computational Aeroacoustic Simulation of Landing Gear". Applied Mechanics and Materials 421 (septiembre de 2013): 110–15. http://dx.doi.org/10.4028/www.scientific.net/amm.421.110.
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RANS / NLAS numerical simulation method is adopted in this paper to carry out study on the aerodynamic noise analysis of basic landing gear configuration. Reynolds average N-S equation is solved with nonlinear turbulence model to establish the landing gear initial flow field, based on which, the NLAS (nonlinear acoustic solver) processed the turbulence fluctuation reconstruction to obtain the near-field acoustic characteristics of landing gear. Combined with the flow characteristics and the associated noise spectrum analysis, aerodynamic noise characteristics of landing gear are achieved. The work in this paper can provide useful research foundation on the following noise reduction design of landing gear.
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Redonnet, Stephane. "Further assessment of a time domain impedance boundary condition for the numerical simulation of noise-absorbing materials". International Journal of Aeroacoustics 20, n.º 8 (noviembre de 2021): 927–58. http://dx.doi.org/10.1177/1475472x211052701.
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In regard to the mitigation of environmental noise across major industry sectors, the present study focuses on the numerical prediction of passive noise reduction devices. Here, it is further explored how the noise attenuation induced by locally reacting noise absorbing materials (also called acoustic liners) can be simulated using a time domain highly accurate Computational AeroAcoustics (CAA) method. To this end, it is assessed how a classical Time Domain Impedance Boundary Condition (TDIBC) can effectively model acoustic liners of practical interest, including when the latter are exposed to realistic conditions (grazing flow and noise excitation). The investigation consists in numerically reproducing two experimental campaigns initially performed at NASA Langley Research Center. Two different materials are considered (honeycomb superimposed with perforate or wiremesh resistive face-sheet), each being characterized by a specific noise attenuation behaviour ( e.g. dependency on the flow conditions and/or noise excitation). Each material is tested under various flow conditions ( e.g. grazing flow of Mach up to 0.5) and/or noise source excitation ( e.g. multiple tones of level up to 140 dB each). The results demonstrate the ability of the underlying CAA/TDIBC approach to simulate realistic acoustic liners in non-trivial configurations, with enough physical accuracy ( e.g. correct capture of the noise attenuation characteristics) and numerical robustness ( e.g. absence of instabilities). The study also reveals that, independent from the CAA/TDIBC approach itself, some specific pre-processing tasks (e.g. impedance eduction and subsequent TDIBC calibration) may play a bigger role than expected, in practice.
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Battista, Gianmarco, Marcello Vanali, Paolo Chiariotti y Paolo Castellini. "A comparison between aeroacoustic source mapping techniques for the characterisation of wind turbine blade models with microphone arrays". ACTA IMEKO 10, n.º 4 (30 de diciembre de 2021): 147. http://dx.doi.org/10.21014/acta_imeko.v10i4.1142.
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<p class="Abstract">Characterising the aeroacoustic noise sources generated by a rotating wind turbine blade provides useful information for tackling noise reduction of this mechanical system. In this context, microphone array measurements and acoustic source mapping techniques are powerful tools for the identification of aeroacoustic noise sources. This paper discusses a series of acoustic mapping strategies that can be exploited in this kind of applications. A single-blade rotor was tested in a semi-anechoic chamber using a circular microphone array. <br />The Virtual Rotating Array (VRA) approach, which transforms the signals acquired by the physical static array into signals of virtual microphones synchronously rotating with the blade, hence ensuring noise-source stationarity, was used to enable the use of frequency domain acoustic mapping techniques. A comparison among three different acoustic mapping methods is presented: Conventional Beamforming, CLEAN-SC and Covariance Matrix Fitting based on Iterative Re-weighted Least Squares and Bayesian approach. The latter demonstrated to provide the best results for the application and made it possible a detailed characterization of the noise sources generated by the rotating blade at different operating conditions.</p>
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Dannemann, Martin, Michael Kucher, Eckart Kunze, Niels Modler, Karsten Knobloch, Lars Enghardt, Ennes Sarradj y Klaus Höschler. "Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects". Applied Sciences 8, n.º 10 (15 de octubre de 2018): 1923. http://dx.doi.org/10.3390/app8101923.
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In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise absorption for HR liners is presented. By replacing rigid cell walls in the liner’s honeycomb core structure by flexible polymer films, additional acoustic energy is dissipated. A manufacturing technology for square honeycomb cores with partially flexible walls is described. Samples with different flexible wall materials were fabricated and tested. The acoustic measurements show more broadband sound absorption compared to a reference liner with rigid walls due to acoustic-structural interaction. Manufacturing-related parameters are found to have a strong influence on the resulting vibration behaviour of the polymer films, and therefore on the acoustic performance. For future use, detailed investigations to ensure the liner segments compliance with technical, environmental, and life-cycle requirements are needed. However, the results of this study show the potential of this novel liner concept for noise reduction in future aero-engines.
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D’Elia, Massimo Emiliano, Thomas Humbert y Yves Aurégan. "On articulated plates with micro-slits to tackle low-frequency noise". Acta Acustica 5 (2021): 31. http://dx.doi.org/10.1051/aacus/2021024.
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In recent years, new concepts of acoustic absorbers dedicated to the reduction of low-frequency noise have been developed. Among them, liners with moving parts, such as membrane-based liners, have been an object of particular interest. In the present paper, we propose a liner concept based on a cantilever beam made of articulated plates with micro-slits. Compared to membrane technologies, these micro-slits introduce a small leakage from the backing cavity that reduces the high compressibility effects occurring at very low frequencies in a small cavity. An acoustic liner including an ensemble of such articulated plates has been fabricated and characterized for grazing acoustic incidence in absence and in presence of flow. Measurements in an impedance tube at normal incidence have also been performed, and perfect absorption is obtained at a frequency where the liner thickness corresponds to 1/16th of the acoustic wavelength. A new and simple model is proposed to predict the attenuation of this type of acoustic treatment. The results are in good agreement with the measurements, indicating a correct identification of the physical phenomena here at stake.
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Heo, Hyeonu, Mathew Sofield, Jaehyung Ju y Arup Neogi. "Acoustic Metasurface-Aided Broadband Noise Reduction in Automobile Induced by Tire-Pavement Interaction". Materials 14, n.º 15 (30 de julio de 2021): 4262. http://dx.doi.org/10.3390/ma14154262.
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The primary noise sources of the vehicle are the engine, exhaust, aeroacoustic noise, and tire–pavement interaction. Noise generated by the first three factors can be reduced by replacing the combustion engine with an electric motor and optimizing aerodynamic design. Currently, a dominant noise within automobiles occurs from the tire–pavement interaction over a speed of 70–80 km/h. Most noise suppression efforts aim to use sound absorbers and cavity resonators to narrow the bandwidth of acoustic frequencies using foams. We demonstrate a technique utilizing acoustic metasurfaces (AMSes) with high reflective characteristics using relatively lightweight materials for noise reduction without any change in mechanical strength or weight of the tire. A simple technique is demonstrated that utilizes acoustic metalayers with high reflective characteristics using relatively lightweight materials for noise reduction without any change in mechanical strength or weight of the tire. The proposed design can significantly reduce the noise arising from tire–pavement interaction over a broadband of acoustic frequencies under 1000 Hz and over a wide range of vehicle speeds using a negative effective dynamic mass density approach. The experiment demonstrated that the sound transmission loss of AMSes is 2–5 dB larger than the acoustic foam near the cavity mode, at 200–300 Hz. The proposed approach can be extended to the generalized area of acoustic and vibration isolation.
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Zheng, Zhongquan Charlie, Tayanne Alves, Jiacheng Hou y Huixuan Wu. "Simulation of acoustic liner performance in a grazing flow duct". Journal of the Acoustical Society of America 151, n.º 4 (abril de 2022): A55. http://dx.doi.org/10.1121/10.0010639.
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Acoustic liners are commonly used to reduce aircraft engine noise. The performance of acoustic liners can be tested in a grazing flow duct. In order to simulate the new extended-reaction liners which allow lateral acoustic propagation inside the liner, finite element methods have been used in the frequency domain computation. In this study, different liner core materials, including honeycomb and foam-metal, are simulated with uniform or varied material properties and geometries. Frequency responses of liners are studied with different materials under several flow conditions. An immersed-boundary, time-domain simulation is also implemented to simulate the broad-band behavior of the liners and to compare with the frequency-domain computation. Optimized material properties and liner arrangement for noise reduction will be investigated.
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Zhou, Shuiqing y Jun Wang. "Prediction and Reduction of Aerodynamic Noise of the Multiblade Centrifugal Fan". Advances in Mechanical Engineering 6 (1 de enero de 2014): 712421. http://dx.doi.org/10.1155/2014/712421.
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An aerodynamic and aeroacoustic investigation of the multiblade centrifugal fan is proposed in this paper, and a hybrid technique of combining flow field calculation and acoustic analysis is applied to solve the aeroacoustic problem of multiblade centrifugal fan. The unsteady flow field of the multiblade centrifugal fan is predicted by solving the incompressible Reynolds-averaged Navier-Stokes (RANS) equations with conventional computing techniques for fluid dynamics. The principal noise source induced is extracted from the calculation of the flow field by using acoustic principles, and the modeled sources on inner and outer surfaces of the volute are calculated with multiregional boundary element method (BEM). Through qualitative analysis, the sound pressure amplitude distribution of the multiblade centrifugal fan in near field is given and the sound pressure level (SPL) spectrum diagram of monitoring points in far field is obtained. Based on the analysis results, the volute tongue structure is adjusted and then a low-noise design for the centrifugal fan is proposed. The comparison of noise tests shows the noise reduction of improved fan model is more obvious, which is in good agreement with the prediction using the hybrid techniques.
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Qiu, S., WB Song y H. Liu. "Shape optimization of a general bypass duct for tone noise reduction using continuous adjoint method". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, n.º 1 (25 de marzo de 2013): 119–34. http://dx.doi.org/10.1177/0954406213481915.
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A novel continuous adjoint-based acoustic propagation method is proposed for low-noise turbofan duct design. A fan bypass duct tonal noise propagation model that is verified by comparison with an analytical solution of the modal radiation from a semi-infinite duct with the shear layer is enhanced with its continuous adjoint formulation, having been applied to design the bypass duct. First, this article presents the complete formulation of the time-dependent optimal design problem. Second, a continuous adjoint-based acoustic propagation method for two-dimensional bypass duct configurations is derived and presented. This article aims at describing the potential of the adjoint technique for aeroacoustic shape optimization. The implementation of the unsteady aeroacoustic adjoint method is validated by comparing the sensitivity derivative with that obtained by finite differences. Using a continuous adjoint formulation, the necessary aerodynamic gradient information is obtained with large computational savings over traditional finite-difference methods. The examples presented demonstrate that the combination of a continuous-adjoint algorithm with a noise prediction method can be an efficient design tool in the bypass duct noise design problem.
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Azimi, Mohammadreza, Fathollah Ommi y Naghmeh Jamshidi Alashti. "Using Acoustic Liner for Fan Noise Reduction in Modern Turbofan Engines". International Journal of Aeronautical and Space Sciences 15, n.º 1 (30 de marzo de 2014): 97–101. http://dx.doi.org/10.5139/ijass.2014.15.1.97.
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Arif, Irsalan, Randolph C. K. Leung y Muhammad Rehan Naseer. "A computational study of trailing edge noise suppression with embedded structural compliance". JASA Express Letters 3, n.º 2 (febrero de 2023): 023602. http://dx.doi.org/10.1121/10.0017321.
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A unique concept for suppression of trailing edge noise scattering from a splitter plate in a low Reynolds number flow is proposed. The key idea of the concept is the adoption of a structural compliance system embedded with a finite number of elastic panels. Specific compliance system designs are devised for promotion of panel structural resonance that effectively absorbs broadband flow/acoustic fluctuation energy responsible for noise scattering. The concept is examined using high-fidelity direct aeroacoustic simulation together with spatiotemporal aeroacoustic-structural interaction analysis. The concept is confirmed feasible and outperforms many similar trailing edge noise reduction approaches reported in the literature.
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Murata, Yo, Tatsuya Ishii, Shunji Enomoto, Hideshi Oinuma, Kenichiro Nagai, Junichi Nagai y Hirofumi Daiguji. "Fan Noise Reduction by Acoustic Liners Combined with Fine-Perforated-Film: Noise Tests by a Small Turbofan Engine DGEN 380". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 5 (1 de febrero de 2023): 2966–79. http://dx.doi.org/10.3397/in_2022_0418.
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Resonant-type liner panels are one the primary countermeasures for the fan noise of aircraft engines, though the sound absorption performances of the liners are known to be tolerated by the grazing flow streaming on their surface. Therefore, suppressing the effect of the flow on the liners is greatly important for higher sound absorption efficiency. In this study, liner panels with special surface structures were manufactured and applied to an outdoor test using a small turbofan engine, DGEN 380. A special thin film, Fine-Perforated-Film (FPF), was applied to two liner samples. In the first sample, FPF was applied directly to the surface of a typical liner. In the second sample, a gap was fixed between the FPF and liner surface. In addition, a rigid wall and a typical liner were used for comparison, to investigate the effect of the structures. During the test, the samples were installed to the exhaust bypass duct of the DGEN engine. The acoustic pressure inside the duct and in far field was measured. Analysis and comparison of the results showed that the new structures suppressed the effect of the grazing flow and caused a larger amount of noise reduction, compared to the typical liner sample.
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Guo, Jingwen, Renhao Qu, Yi Fang, Siyang Zhong y Xin Zhang. "Broadband noise attenuation in the flow duct using metamaterial-based acoustic liners". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 3 (1 de febrero de 2023): 4666–73. http://dx.doi.org/10.3397/in_2022_0675.
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An acoustic liner design based on metamaterial is proposed for broadband duct noise reduction. The material is constructed by four periodically arranged partitions-embedded units covered by a perforated plate, forming a linear reflected phase-shifting within 0 to 2π in a wide target frequency range. The sound absorption performance under normal incident waves is firstly examined by both numerical simulation and impedance tube measurement, leading to close agreement to the target design. Then, the meta-liner is installed in a flow tube to assess its capability of reducing broadband noise in a duct with aerodynamic flows. The experiments investigations are performed in an advanced grazing flow tube developed at the Hong Kong University of Science and Technology. The effect of sound levels (ranging from 120dB to 140dB), flow speeds with the Mach number up to 0.3, and the position of sound source (at upstream and downstream sides of meta-liner) are investigated. Results show that a nearly flat transmission loss is achieved in the target frequency range by the metamaterial-based acoustic liner in various conditions, showing its potential for practical industrial applications.
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Arif, Muhammad Irsalan, Randolph Chi Kin Leung, Garret Lam y Muhammad Rehan Naseer. "Fluid-Structure Interactions and Aeroacoustic coupling of Airfoil with Flexible Membrane(s)". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n.º 3 (1 de febrero de 2023): 4166–77. http://dx.doi.org/10.3397/in_2022_0594.
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In this paper, fluid-structure interactions of a NACA 0012 airfoil mounted with short flexible membrane(s) and its coupling effect on airfoil aeroacoustics are presented. A time-domain direct aeroacoustic simulation coupled with structural dynamics is carried out at a low Reynolds number of 50,000 to explore the aeroacoustic-structural interactions. Two different airfoil configurations based on single and dual membranes are analyzed. The membrane deflections and their impact on the flow field are characterized in wavenumber-frequency domain to analyze the structural dynamics due to flow unsteadiness within the laminar boundary layer and the resulting acoustic waves emanating from the airfoil trailing edge. A strong correlation between the membrane displacement and downstream propagating flow is observed for all configurations whereas the correlation is considerably weakened between the membrane displacement and upstream acoustic waves which ultimately results in the airfoil self-noise reduction without affecting the airfoil aerodynamics. The extent of noise reduction for dual membrane airfoil configuration is observed to be considerably higher than the single membrane airfoil configuration which corresponds to a much lower correlation among the upstream propagating acoustic waves and membrane deflection for both the membranes and redistribution of upstream flow energy into different frequencies.
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Hattori, Yuji y Ryu Komatsu. "Mechanism of aeroacoustic sound generation and reduction in a flow past oscillating and fixed cylinders". Journal of Fluid Mechanics 832 (26 de octubre de 2017): 241–68. http://dx.doi.org/10.1017/jfm.2017.668.
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The aeroacoustic sound generated in a flow past two cylinders, one of which is oscillating and the other is fixed, is studied by direct numerical simulation. This problem involves key ingredients of the aeroacoustic noise generated from wind turbines, helicopters, axial flow fans and other turbomachinery: flow, a moving body and a fixed body. The corrected volume penalization method is successfully applied to resolve the sound pressure of aeroacoustic waves as a solution of the compressible Navier–Stokes equations. The sound pressure was shown to be in good agreement with the prediction by the Ffowcs Williams–Hawkings aeroacoustic analogy, which takes account of the cylinder motion, confirming the accuracy of the corrected volume penalization method. Prior to the case of two cylinders, sound generation in flow past a single oscillating cylinder is considered. The fluid motion can be either periodic or non-periodic depending on the frequency and the amplitude of cylinder oscillation. The acoustic power is significantly reduced when the fluid motion locks in to a frequency lower than the natural frequency of vortex shedding from a fixed cylinder. When a fixed cylinder is added, the acoustic power depends strongly on the distance between the cylinders, since that determines whether synchronization occurs and the phase difference between the three forces: the lift forces exerted on the two cylinders and the inertial force due to volume displacement effect of the oscillating cylinder. In particular, significant sound reduction is observed when the fixed cylinder is placed upstream and the frequency of the cylinder oscillation is set to the frequency for which the acoustic power is minimized in the single-cylinder case.
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Palma, Giorgio y Lorenzo Burghignoli. "On the integration of acoustic phase-gradient metasurfaces in aeronautics". International Journal of Aeroacoustics 19, n.º 6-8 (10 de septiembre de 2020): 294–309. http://dx.doi.org/10.1177/1475472x20954404.
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Metamaterials might be one of the breakthrough technologies needed from the aeronautic industry to achieve the more and more challenging targets set by the international authorities, especially about noise emissions. In this article, a theoretical link between Transformation Acoustics and Generalized Snell’s Law, two widely used metamaterial models, is demonstrated analytically and applied to case studies. The relevance of the connection in the aeroacoustic field is discussed along with the consequent computational advantages for numerical simulations. This is exploited to perform a simulation-based design optimization of a phase-graded metasurface acoustic lining of a 2 D duct in presence of flow. Results show promising abilities of the optimized device to modify and control the directivity of the noise emitted from the duct by means of unconventional reflections. The noise reduction in the desired direction is obtained through constructive and destructive interference, with no absorption from the boundaries.
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Horowitz, S. B., T. Nishida, L. N. Cattafesta y M. Sheplak. "Characterization of a Compliant-Backplate Helmholtz Resonator for An Electromechanical Acoustic Liner". International Journal of Aeroacoustics 1, n.º 2 (agosto de 2002): 183–205. http://dx.doi.org/10.1260/147547202760236969.
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Passive acoustic liners are currently used to reduce the noise radiated from aircraft engine nacelles. This study is the first phase in the development of an actively-tuned electromechanical acoustic liner that potentially offers improved noise suppression over conventional multi-layer liners. The underlying technical concept is based on the idea that the fundamental frequency of a Helmholtz resonator may be adjusted by adding degrees of freedom (DOF) via substitution of a rigid wall with a piezoelectric composite diaphragm coupled to a passive electrical shunt network. In this paper, a Helmholtz resonator containing a compliant aluminum diaphragm is investigated to provide a fundamental understanding of this two DOF system, before adding complexity via the piezoelectric composite material. Using lumped elements, an equivalent circuit model is derived, from which the transfer function and acoustic impedance are obtained. Additionally, a mass ratio is introduced that quantifies the amount of coupling between the elements of the system. The theory is then compared to experiment in a normal-incidence impedance tube. The experimental results confirm the additional DOF and overall acoustic behavior but also suggest the need for a more comprehensive analytical model to accurately predict the acoustic impedance. Nevertheless, the experiments demonstrate the potential benefits of this approach for the reduction of aircraft engine noise.
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Münsterjohann, Sven, Florian Zenger y Stefan Becker. "Efficient and Noise Reduced Design of a Side Channel Blower Considering Psychoacoustic Evaluation Criteria". Applied Mechanics and Materials 856 (noviembre de 2016): 174–80. http://dx.doi.org/10.4028/www.scientific.net/amm.856.174.
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Commonly used turbo machines like axial fans or side channels blowers have a large impact on their environment: Large demand for electrical power and production of strong aeroacoustic sound sources, generating a significant noise emission, lead to a environmental footprint. The current work addresses both tasks: improvement of efficiency and reduction of noise emission. In this work a side channel blower is in the focus of the investigations. Since the noise emission of side channel blowers mainly occurs in the region of the stripper, pressure measurements on the blade surface are performed. The pressure trend during the blade passage along the stripper provides information on the exact location of and the contribution to the acoustic noise generation. Modifications of the stripper geometry with the objective of pressure drop linearization along the stripper are evaluated with respect to efficiency, pressure rise and noise reduction. All acoustic measurements are also evaluated with psychoacoustic quantities, like loudness and sharpness, to account for the human perception.
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Qiu, Sheng. "A continuous adjoint-based aeroacoustic shape optimization for multi-mode duct acoustics". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, n.º 21 (24 de noviembre de 2017): 3897–914. http://dx.doi.org/10.1177/0954406217743273.
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A multi-mode adjoint-based optimization method is proposed for the noise reduction optimization in multi-mode duct acoustics problems. The objective is to minimize the amplitude of sound from an inlet duct on the wall and integral line while maintaining the aerodynamic performance. The complete detailed derivation of the adjoint equations and their corresponding adjoint boundary conditions are presented firstly based on the multi-mode linear Euler equations. With the solved adjoint variables, the final expression of the cost function gradient with respect to the design variables is formulated. The sensitivity derivative computed by the continuous adjoint method is validated by comparing with that obtained using finite difference method. Up to 50 design variables are involved in the adjoint optimization to ensurely provide an adequate design space. And a quasi-Newton Broyden–Fletcher–Goldfarb–Shanno algorithm is utilized to determine an improved intake duct geometry based on the objective function gradient provided by the adjoint solution. Finally, two multi-mode optimization of a typical inlet duct confirms the flexibility of the multi-mode adjoint-based framework and the efficiency of the multi-mode adjoint-based technique.
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Serré, Ronan, Nicolas Gourdain, Thierry Jardin, Marc C. Jacob y Jean-Marc Moschetta. "Towards silent micro-air vehicles: optimization of a low Reynolds number rotor in hover". International Journal of Aeroacoustics 18, n.º 8 (noviembre de 2019): 690–710. http://dx.doi.org/10.1177/1475472x19890260.
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The demand in micro-air vehicles is increasing as well as their potential missions. Either for discretion in military operations or noise pollution in civilian use, noise reduction of micro-air vehicles is a goal to achieve. Aeroacoustic research has long been focusing on full scale rotorcrafts. At micro-air vehicle scales however, the hierarchization of the numerous sources of noise is not straightforward, as a consequence of the relatively low Reynolds number that ranges typically from 5000 to 100,000 and low Mach number of approximately 0.1. This knowledge, however, is crucial for aeroacoustic optimization and blade noise reduction in drones. This contribution briefly describes a low-cost, numerical methodology to achieve noise reduction by optimization of micro-air vehicle rotor blade geometry. Acoustic power measurements show a reduction of 8 dB(A). The innovative rotor blade geometry allowing this noise reduction is then analysed in detail, both experimentally and numerically with large eddy simulation using lattice Boltzmann method. Turbulence interaction noise is shown to be a major source of noise in this configuration of low Reynolds number rotor in hover, as a result of small scale turbulence and high frequency unsteady aeroadynamics impinging the blades at the leading edge.
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Ragni, Daniele, Francesco Avallone y Damiano Casalino. "Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations". Measurement Science and Technology 33, n.º 6 (9 de marzo de 2022): 062001. http://dx.doi.org/10.1088/1361-6501/ac547d.
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Abstract 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 starts with a deep understanding of the underlying mechanisms of noise generation. To elucidate the physics behind the onset 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 proposed 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 a historical overview, to quickly bridge to the measurement techniques and the facilities employed by the scientific community. Being the measurement principles already reported in the literature, this review only focuses on the most relevant studies trying to relate the 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 related to the instrumentation.
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Kopania, Joanna M. "Bionics - Natural but Innovative Methods Improve the Aeroacoustic Engineering". Applied Mechanics and Materials 806 (noviembre de 2015): 222–31. http://dx.doi.org/10.4028/www.scientific.net/amm.806.222.
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This paper presents the aeroacoustics result of the trailing edge noise prepared wings two species of owl - Barn owl (Tyto alba), called “good hearing” and Northern hawk-owl (Surnia ulula), called “good seeing”. The acoustic performance comparisons between the Barn owl and Northern hawk-owl show that there are differences between the sound intensity the studied wings. These results prove that the special sound suppression characteristics of wing feather play an important role for their silent flight. Therefore the flat plates with the cutting trailing edge have been studied. At lower speeds, a better noise reduction effect was obtained for the plates with edges as elliptical arcs. On the basis of the above tests it can be concluded that other types of notches on the trailing edge (not just a sawtooth) also reduce the aerodynamic noise of flat plate.
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Ayton, Lorna J. "Acoustic scattering by a finite rigid plate with a poroelastic extension". Journal of Fluid Mechanics 791 (24 de febrero de 2016): 414–38. http://dx.doi.org/10.1017/jfm.2016.59.
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The scattering of sound by a finite rigid plate with a finite poroelastic extension interacting with an unsteady acoustic source is investigated to determine the effects of porosity, elasticity and the length of the extension when compared to a purely rigid plate. The problem is solved using the Wiener–Hopf technique, and an approximate Wiener–Hopf factorisation process is implemented to yield reliable far-field results quickly. Importantly, finite chord-length effects are taken into account, principally the interaction of a rigid leading-edge acoustic field with a poroelastic trailing-edge acoustic field. The model presented discusses how the poroelastic trailing-edge property of owls’ wings could inspire quieter aeroacoustic designs in bladed systems such as wind turbines, and provides a framework for analysing the potential noise reduction of these designs.
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Simon, Frank, R. Roncen, P. Vuillemin, P. Klotz, Fabien Méry y E. Piot. "Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform description". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 6 (1 de agosto de 2021): 508–18. http://dx.doi.org/10.3397/in-2021-1496.
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In the context of aircraft noise reduction in varied applications where a cold or hot shear grazing flow is present (i.e., engine nacelle, combustion chamber, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency regime, where space constraints limit the efficiency of conventional liner technology. Therefore, liner design must take into account the dimensional and phenomenological characteristics of constituent materials, assembly specifications and industrial requirements involving multiphysical phenomena. To perform the single/multi-objective optimization of complex meta-surface liner candidates, a software platform coined OPAL (OPtimisation of Acoustic Liners) was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial elementary acoustic layers along a given duct. Then, the physical properties of this liner can be optimized, relatively to weighted objectives, for a given flow and frequency range: impedance target, maximum absorption coefficient or transmission loss with a total sample size and weight... The presentation will focus on the different elementary bricks and assembly of a problem (from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin simulations of the Linearized Euler Equations).
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Eltaweel, Ahmed, Meng Wang, Dongjoo Kim, Flint O. Thomas y Alexey V. Kozlov. "Numerical investigation of tandem-cylinder noise reduction using plasma-based flow control". Journal of Fluid Mechanics 756 (2 de septiembre de 2014): 422–51. http://dx.doi.org/10.1017/jfm.2014.420.
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AbstractThe noise of flow over tandem cylinders at $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\mathit{Re}}_D= 22\, 000$ and its reduction using single dielectric barrier discharge (SDBD) plasma actuators are simulated numerically both to confirm and extend experimental results. The numerical approach is based on large-eddy simulation (LES) for the turbulent flow field, a semi-empirical plasma actuation model, and Lighthill’s theory for acoustic calculation. Excellent agreement between LES and experimental results is obtained for both the baseline flow and flow with plasma control in terms of wake velocity profiles, turbulence intensity, and frequency spectra of pressure fluctuations on the downstream cylinder. The validated flow-field results allow an accurate acoustic analysis based on Lighthill’s equation, which is solved using a boundary-element method. The effectiveness of plasma actuators for reducing noise is clearly demonstrated. In the baseline flow, the acoustic field is dominated by the interaction between the downstream cylinder and the upstream wake. Through suppression of vortex shedding from the upstream cylinder, the interaction noise is reduced drastically by the plasma flow control, and the vortex-shedding noise from the downstream cylinder becomes equally important. At a free-stream Mach number of 0.2, the peak sound pressure level is reduced by approximately 16 dB. This suggests the viability of plasma actuation for active aeroacoustic control of airframe noise.
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Zhao, Kun, Yong Liang, Tingrui Yue, Zhengwu Chen y Gareth J. Bennett. "Characterization of the aircraft bay/landing gear coupling noise at low subsonic speeds and its suppression using leading-edge chevron spoiler". Advances in Mechanical Engineering 11, n.º 8 (agosto de 2019): 168781401987143. http://dx.doi.org/10.1177/1687814019871431.
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When the aircraft opens the bay door to let the landing gear either drop or retract, the incoming flow will result in a significant amount of coupling noise from the bay and the landing gear. Here, an experimental study was reported to characterise the acoustic performance and flow field at low subsonic speeds. Also, we examined a passive control method leading-edge chevron spoiler to suppress the noise. The experiment was performed in a low-speed aeroacoustic wind, the bay was simplified as a rectangular cavity and the spoiler was mounted to the leading edge. Both acoustic and aerodynamic measurements were performed through two microphone arrays, pressure transducers and particle image velocimetry. It was found that installation of the landing gear model can attenuate cavity oscillation noise to some extent by disturbing the shear layer of the cavity leading edge. Moreover, acoustic measurement confirmed the noise control when the spoiler was used. In addition, a parametric study on the effects of chevron topology was performed, and an optimised value was found for each parameter. From the aerodynamic measurement, the noise reduction was explained from the perspective of fluid dynamics. It was observed that installation of the chevron can raise the leading-edge shear layer and break up the large-scale vortices, thereby controlling the Rossiter mode noise and the landing gear model noise at certain frequencies.
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Watkins, Joseph y Abdessalem Bouferrouk. "The Effects of a Morphed Trailing-Edge Flap on the Aeroacoustic and Aerodynamic Performance of a 30P30N Aerofoil". Acoustics 4, n.º 1 (3 de marzo de 2022): 248–67. http://dx.doi.org/10.3390/acoustics4010015.
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This paper presents initial results on the aeroacoustic and aerodynamic effects of morphing the trailing-edge flap of the 30P30N aerofoil, over five flap deflections (5–25°), at an 8° angle of attack and a Reynolds number of Re=9.2×105. The Ffowcs-Williams–Hawkings acoustic analogy estimates the far-field noise, whilst the flow field is solved using URANS with the four-equation Transition SST model. Aerodynamic and aeroacoustic simulation data for the 30P30N’s full configuration compare well with experimental results. A Courant number (C) ≤ 1 should be used for resolving tonal noise, whilst a C of up to 4 is sufficient for broadband noise. Sound pressure level results show an average 11% reduction in broadband noise across all flap deflections and frequencies for the morphed configuration compared with the conventional, single-slotted flap. The morphed flap eliminates the multiple tonal peaks observed in the conventional design. Beyond 15° flap deflection, the morphing flap achieves higher stall angles, but with increased drag, leading to a maximum reduction of 17% in Cl/Cd ratio compared with the conventional flap. The methodology reported here for the 30P30N is a quick tool for initial estimates of the far-field noise and aerodynamic performance of a morphing flap at the design stage.
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Wu, Han, Wangqiao Chen, Hanbo Jiang, Siyang Zhong y Xin Zhang. "Experimental investigation of the effect of sectional airfoil profile deviation on propeller noise". Physics of Fluids 35, n.º 2 (febrero de 2023): 027104. http://dx.doi.org/10.1063/5.0135555.
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The geometry of the sectional airfoil has a determinative impact on the aeroacoustic characteristics of propellers. However, there are always slight deviations in the practical profiles due to manufacturing tolerance, wear loss, and limitations of processing techniques, which can potentially introduce uncertainties to aeroacoustic measurements. To this end, a systematic investigation is conducted on a benchmark propeller with a diameter of 217.2 mm and several of its variants in an anechoic wind tunnel. The variants are redesigned by modifying the sectional airfoil shapes with varying finite trailing-edge thicknesses. High-accuracy computer numerical control machining is employed to ensure the subtle geometrical differences between the blades. Force measurements indicate that the aerodynamic performances are insensitive to the slight variations of the sectional geometry, as expected. As for the acoustic performance, both the tonal and broadband noise are slightly affected when the axial flow speed is lower than 5 m/s. By contrast, a discernible noise reduction above 3 dB can be achieved due to the finite trailing-edge thickness. The noise source features are also investigated using a wavelet-based beamforming method, confirming that the noise reduction is caused by the weakened trailing-edge noise around the tip. This study is beneficial for the quantification of uncertainties in propeller noise measurements. It also suggests that adjusting trailing-edge thickness might be an useful approach in reducing propeller noise in practical applications.
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Cao, Huijing, Teng Zhou, Yinan Zhang y Mingming Zhang. "An experimental investigation of aerodynamic and aeroacoustic performance of a wind turbine airfoil with trailing edge serrations". Journal of the Acoustical Society of America 151, n.º 2 (febrero de 2022): 1211–22. http://dx.doi.org/10.1121/10.0009570.
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Trailing edge (TE) serrations are widely used as an effective passive control method to reduce the turbulent TE noise from wind turbine blades. Other than the acoustic effects, the aerodynamic performance of serrations is also an important issue that should be considered, since it determines the power output of the blade. To this end, the far-field sound pressure level, flow field, and aerodynamic force of the serrated airfoil were measured in an anechoic wind tunnel, and the lift increase and noise reduction effects of the TE serrations were comprehensively evaluated. The result showed that the presence of TE serrations could achieve noise reduction by about 2 dB at the low-to-moderate frequency range at small angles of attack, and meanwhile it could suppress the fluctuation of aerodynamic forces. In addition, the proper orthogonal decomposition method was deployed to decompose the wake flow into various vortex structures with different portions of turbulent kinetic energy so as to reveal the noise reduction mechanism of the serrated TE. The result suggested that TE serrations could effectively inhibit large-scale vortex structures that shed from the boundary layer on the suction side, thereby achieving noise reduction around the vortex shedding frequency.
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Kan, Zi, Daochun Li, Shiwei Zhao, Jinwu Xiang y Enlai Sha. "Aeroacoustic and aerodynamic characteristics of a morphing airfoil". Aircraft Engineering and Aerospace Technology 93, n.º 5 (1 de julio de 2021): 888–99. http://dx.doi.org/10.1108/aeat-11-2020-0263.
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Purpose This paper aims to assess the aeroacoustic and aerodynamic performance of a morphing airfoil with a flexible trailing edge (FTE). The objective is to make a comparison of the aerodynamic noise characteristics between the conventional airfoil with a flap and morphing airfoil and analyse the noise reduction mechanisms of the morphing airfoil. Design/methodology/approach The computational fluid dynamic method was used to calculate the aerodynamic coefficients of morphing airfoil and the Ffowcs-Williams and Hawking’s acoustic analogy methods were performed to predict the far-field noise of different airfoils. Findings Results show that compared with the conventional airfoil, the morphing airfoil can generate higher lift and lower noise, but a greater drag. Additionally, the noise caused by the one-unit lift of the morphing airfoil is significantly lower than that of the conventional airfoil. For the morphing airfoil, the shedding vortex in the trailing edge was the main noise resource. As the angle of attack (AoA) increases, the overall sound pressure level of the morphing airfoil increases significantly. With the increase of the trailing edge deflection angle, the amplitude and the period of sound pressure of the morning airfoil fluctuation increase. Practical implications Presented results could be very useful during designing the morphing airfoil with FTE, which has significant advantages in aerodynamic efficiency and aeroacoustic performance. Originality/value This paper presents the aerodynamic and aeroacoustic characteristics of the morphing airfoil. The effect of trailing edge deflection angle and AoA on morphing airfoil was investigated. In the future, using a morphing airfoil instead of a traditional flap can reduce the aircraft`s fuel consumption and noise pollution.
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Sandu, Constantin, Thomas Humbert, Yves Auregan, Marius Deaconu, Andrei Totu, Andrei Radu, Horatiu Serbescu y Traian Tipa. "Innovative liner concept using friction powder for increasing of broadband noise absorption. Applications for broadband noise absorption in fan duct". IOP Conference Series: Materials Science and Engineering 1226, n.º 1 (1 de febrero de 2022): 012049. http://dx.doi.org/10.1088/1757-899x/1226/1/012049.
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Abstract This paper presents research related influence of friction powders on enlarging the absorption band of acoustic liners used for reduction of tonal noise in fan duct of aero-engine. Kundt tube measurements done at COMOTI using fine powders (granules) made of various light-weight materials placed in the honeycomb cells of SDOF liners have shown a considerable broadening of the absorbed band of frequencies without a significant decreasing of absorption at the resonance frequency. Although the phenomenon is generally present for any type of powder, it was observed that for some powders the absorption is higher than for others. On the other hand, it was observed that the effect of the filling percentage of the cavity is important. Then, experiments done at the grazing flow facility of CNRS-Le Mans University have shown that the phenomenon is also present for high acoustic incident levels (up to 140dB) and M=0.13 while it still depends by the nature of powder material. The best results were obtained for the cork powder when the honeycomb is filled with powder at 66% of its height. For this material, the broadening of the transmission loss well was maximum. This phenomenon could be explained by the apparition of friction between powder granules which are taking place at very low scale consuming the noise power on a broader range of frequencies. It is supposed that the friction between the particles of powder have major influence because the best noise absorption was obtained for powders with a large distribution of particles’ dimensions while for particles with a small dimensional distribution (expanded polyester balls, for example) the transmission well broadening was smaller. The friction powders technology is simple and can be easily adapted to existing acoustic liner technologies with small manufacturing costs. This feature is conferred by the fact that powders can be easily poured in the honeycombs at the required height. The friction powder technology can be applied not only for the fan duct. In future, it could also be applied for reduction of jet noise reflected by pressure side of wing and for cabin noise reduction.
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Kopiev, Victor, Ivan Belyaev, Mikhail Zaytsev y Kun Zhao. "An Aeroacoustic Study of Full-Scale and Small-Scale Generic Landing Gear Models with Identical Geometry". Applied Sciences 13, n.º 4 (10 de febrero de 2023): 2295. http://dx.doi.org/10.3390/app13042295.
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The paper reports on the results of acoustic measurements of full-scale and small-scale generic landing gear models, which have identical geometry and differ only by their scales. The large-scale landing gear models were simplified and lack small geometric details, which for the first time allows their results to be directly compared with those for the small-scale models of the same geometry. It is shown that after application of the scaling procedure to their noise spectra, the normalized results for broadband noise of the landing gear models of different scales are in good agreement with each other. This result seems to support the feasibility of developing technologies for low-frequency noise reduction of landing gears based on small-scale tests and allowing refinement of semi-empirical models of noise prediction for different landing gear elements.
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Pascal, L., E. Piot y G. Casalis. "A New Implementation of the Extended Helmholtz Resonator Acoustic Liner Impedance Model in Time Domain CAA". Journal of Computational Acoustics 24, n.º 01 (marzo de 2016): 1550015. http://dx.doi.org/10.1142/s0218396x15500150.
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The application of wall acoustic lining is a major factor in the reduction of aircraft engine noise. The extended Helmholtz Resonator (EHR) impedance model is widely used since it is representative of the behavior of realistic liners over a wide range of frequencies. Its application in time domain CAA methods by means of [Formula: see text]-transform has been the subject of several papers. In contrast to standard liner modeling in time domain CAA, which consists in imposing a boundary condition modeling both the cavities and the perforated sheet of the liner, an alternative approach involves adding the cavities to the computational domain and imposing a condition between these cavities and the duct domain to model the resistive sheet. However, the original method may not be used for broadband acoustics since it implements an impedance condition with frequency independent resistance. This paper describes an extension of this method to implement the EHR impedance model in a time domain CAA method.
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Lissek, Herve, Romain Boulandet, Sami Karkar, Gaël Matten, Manuel Collet y Morvan Ouisse. "Design and assessment of a distributed active acoustic liner concept for application to aircraft engine noise reduction". Journal of the Acoustical Society of America 141, n.º 5 (mayo de 2017): 3643. http://dx.doi.org/10.1121/1.4987870.
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Güzel, Kamil, Thomas Stehle y Hans-Christian Möhring. "Aeroakustisch optimierte Kreissägeblätter/Simulation-based optimization of the aeroacoustic behavior of circular saw blades". wt Werkstattstechnik online 110, n.º 01-02 (2020): 18–23. http://dx.doi.org/10.37544/1436-4980-2020-01-02-20.
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Neben der Einhaltung von gesetzlichen Grenzwerten gibt es insbesondere auch wirtschaftliche Gründe, geeignete Maßnahmen zur Lärmminderung in handwerklichen und industriellen Betrieben durchzuführen. Neben direkten Genesungskosten entstehen in lärmbelasteten Bereichen höhere Lohnkosten sowie höhere Ausfallraten, was eine geringere Produktivität bedingt. Insbesondere beim Kreissägen liegen die Geräuschpegel nahezu immer an oder über den zulässigen Grenzwerten. Dieser Beitrag beschreibt das Vorgehen zur Untersuchung des akustischen Verhaltens von unterschiedlichen Kreissägeblattgeometrien auf Basis von Strömungssimulationen und zeigt Potenziale für eine Lärmminderung durch optimierte Zahn- und Spanraumgeometrien auf. In addition to compliance with legal limit values, economic reasons are also responsible, in particular, for carrying out suitable measures for reducing noise in crafts enterprises and industrial companies. In addition to direct recovery costs, higher labor costs and higher failure rates arise, which results in lower productivity. Especially, when circular sawing the noise levels are usually near or above the allowable limits. This article describes the procedure for investigating the acoustic behavior of different circular saw blade geometries based on flow simulations and shows potentials for noise reduction with optimized tooth and chip space geometries.
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Iemma, Umberto. "An integrated toolchain for the design of aeroacoustic metamaterials: the AERIALIST H2020 project." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 4 (1 de agosto de 2021): 2699–707. http://dx.doi.org/10.3397/in-2021-2207.
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The project AERIALIST (AdvancEd aicRaft-noIse-AlLeviation devIceS using meTamaterials), funded within the Breakthrough Innovation topic of the H2020 program, has closed its activity on May 2020. The objective of the project was the disclosure of the potential of metamaterials in developing disruptive devices for the mitigation of aircraft noise, in order to contribute to the identification of the breakthrough technologies targeted at the achievement of the noise reduction targets foreseen by the ACARE Flightpath 2050. Although targeted to low TRL, AERIALIST has been focused on the development of an integrated toolchain capable to address the entire design loop, from the early conception to the numerical and experimental proof of concept, up to the final design and manufacturing. The toolchain was founded onto four pillars: i) the extension of the acoustic metamaterial theory to aeroacoustics; ii) the exploitation of the latest additive manufacturing technologies; iii) the wind-tunnel assessment of the selected concepts; iv) the identification of a development roadmap towards higher TRL. After three years of activity, the project has attained all its objectives. The present paper is a review of the main outcomes of the project, their application potential and relevance to the ACARE objectives.
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Ju, Shengjun, Zhenxu Sun, Dilong Guo, Guowei Yang, Yeteng Wang y Chang Yan. "Aerodynamic-Aeroacoustic Optimization of a Baseline Wing and Flap Configuration". Applied Sciences 12, n.º 3 (20 de enero de 2022): 1063. http://dx.doi.org/10.3390/app12031063.
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Optimization design was widely used in the high-lift device design process, and the aeroacoustic reduction characteristic is an important objective of the optimization. The aerodynamic and aeroacoustic study on the baseline wing and flap configuration was performed numerically. In the current study, the three-dimensional Large Eddy Simulation (LES) equations coupled with dynamic Smagorinsky subgrid model and Ffowcs–William and Hawkings (FW–H) equation are employed to simulate the flow fields and carry out acoustic analogy. The numerical results show reasonable agreement with the experimental data. Further, the particle swarm optimization algorithm coupled with the Kriging surrogate model was employed to determine optimum location of the flap deposition. The Latin hypercube method is used for the generation of initial samples for optimization. In addition, the relationship between the design variables and the objective functions are obtained using the optimization sample points. The optimized maximum overall sound pressure level (OASPL) of far-field noise decreases by 3.99 dB with a loss of lift-drag ratio (L/D) of less than 1%. Meanwhile, the optimized performances are in good and reasonable agreement with the numerical predictions. The findings provide suggestions for the low-noise and high-lift configuration design and application in high-lift devices.
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Galindo, Gabriel E., Sean D. Peterson, Byron D. Erath, Christian Castro, Robert E. Hillman y Matías Zañartu. "Modeling the Pathophysiology of Phonotraumatic Vocal Hyperfunction With a Triangular Glottal Model of the Vocal Folds". Journal of Speech, Language, and Hearing Research 60, n.º 9 (18 de septiembre de 2017): 2452–71. http://dx.doi.org/10.1044/2017_jslhr-s-16-0412.
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Purpose Our goal was to test prevailing assumptions about the underlying biomechanical and aeroacoustic mechanisms associated with phonotraumatic lesions of the vocal folds using a numerical lumped-element model of voice production. Method A numerical model with a triangular glottis, posterior glottal opening, and arytenoid posturing is proposed. Normal voice is altered by introducing various prephonatory configurations. Potential compensatory mechanisms (increased subglottal pressure, muscle activation, and supraglottal constriction) are adjusted to restore an acoustic target output through a control loop that mimics a simplified version of auditory feedback. Results The degree of incomplete glottal closure in both the membranous and posterior portions of the folds consistently leads to a reduction in sound pressure level, fundamental frequency, harmonic richness, and harmonics-to-noise ratio. The compensatory mechanisms lead to significantly increased vocal-fold collision forces, maximum flow-declination rate, and amplitude of unsteady flow, without significantly altering the acoustic output. Conclusion Modeling provided potentially important insights into the pathophysiology of phonotraumatic vocal hyperfunction by demonstrating that compensatory mechanisms can counteract deterioration in the voice acoustic signal due to incomplete glottal closure, but this also leads to high vocal-fold collision forces (reflected in aerodynamic measures), which significantly increases the risk of developing phonotrauma.
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(Henry) Jia, Zhongqi, Seongkyu Lee, Kalki Sharma y Kenneth S. Brentner. "Aeroacoustic Analysis of a Lift-Offset Coaxial Rotor Using High-Fidelity CFD/CSD Loose Coupling Simulation". Journal of the American Helicopter Society 65, n.º 1 (1 de enero de 2020): 1–15. http://dx.doi.org/10.4050/jahs.65.012011.
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This paper presents the aeroacoustic analysis of a lift-offset coaxial rotor in high-speed forward flight using the high-fidelity computational fluid dynamics/computational structural dynamics (CFD/CSD) loose coupling software Helios. Acoustic simulations are performed using the software PSU-WOPWOP at eight microphones positioned below the coaxial rotor. The total power of the three speed cases—100, 150, and 200 kt—is validated against flight-test data and shows good agreement. A series of parametric studies is also conducted to investigate the effect of lift offset, flight speed, and rotor-to-rotor separation distance on acoustics of the coaxial rotor. Strong blade-crossover and self-blade–vortex interaction events of the coaxial rotor, which are major sources of loading noise, are captured via high-fidelity CFD simulations in all speed cases. Highly impulsive acoustic pressure signals are identified in all simulation cases, and the magnitude of mid-frequency sound pressure level (SPL) increases significantly with increasing flight speed and lift offset. The strength of mid-frequency SPL, on the other hand, is reduced significantly as the rotor-to-rotor separation distance increases at 100 kt. However, the higher speed cases do not show a significant reduction in mid-frequency SPL with increasing separation distance.
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Ogura, Keita, Yoimi Kojima, Masato Imai, Kohei Konishi, Kazuyuki Nakakita y Masaharu Kameda. "Reduction in Airfoil Trailing-Edge Noise Using a Pulsed Laser as an Actuator". Actuators 12, n.º 1 (16 de enero de 2023): 45. http://dx.doi.org/10.3390/act12010045.
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Trailing-edge noise (TE noise) is an aeroacoustic sound radiated from an isolated airfoil in the specific ranges of low-speed flow. We used a pulsed laser as an actuator to reduce the TE noise without modifying the airfoil’s surface. The wind tunnel test was conducted to verify the capability of an Nd:YAG laser as the actuator. The laser beam was focused into the air just outside the velocity boundary layer on the lower side of an NACA0012 airfoil. The experimental result shows that the TE noise is suppressed for a certain period after beam irradiations. We then analyzed the physical mechanism of the noise reduction with the laser actuation by the implicit large eddy simulation (ILES), a high-fidelity numerical method for computational fluid dynamics (CFD). The numerical investigations indicate that the pulsed energy deposition changes the unstable velocity amplification mode of the boundary layer, the source of an acoustic feedback loop radiating the TE noise, to another mode that does not generate the TE noise. The sound wave attenuation is observed once the induced velocity fluctuations and consequently generated vortices sweep out the flow structure of the unstable mode. We also examined the effect of the laser irradiation zone’s shape by numerical simulations. The results show that the larger irradiation zone, which introduces the disturbances over a wider range in the span direction, is more effective in reducing the TE noise than the shorter focusing length with the same energies.
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Zhu, Tao y Thomas H. Carolus. "Axial fan tip clearance noise: Experiments, Lattice–Boltzmann simulation, and mitigation measures". International Journal of Aeroacoustics 17, n.º 1-2 (24 de febrero de 2018): 159–83. http://dx.doi.org/10.1177/1475472x17743627.
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The effect of tip clearance in an axial fan on its aerodynamic and aeroacoustic performance is investigated experimentally as well as via a Lattice–Boltzmann flow simulation method. An increase in tip clearance degrades fan pressure rise and efficiency, but also increases significantly the overall sound power emitted by the fan. A large tip clearance causes a clear structure of well distinguishable unsteady vortices which interact with neighboring blades and hence produce an increase in broadband sound. Moreover, if, compared to the design flow rate, there is a moderate flow rate reduction, the local tip vortex systems of all individual blade tips form a circumferentially coherent flow structure, resulting in distinct humps of sound pressure in the acoustic far field. By means of a rigid ring-type protrusion fixed to the inner casing wall, the generation of the tip clearance vortices and slowly rotating coherent flow structures could be suppressed. As a consequence, the sound emitted by the fan is substantially reduced.
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Arif, Irsalan, Garret C. Y. Lam, Randolph C. K. Leung y Muhammad Rehan Naseer. "Distributed surface compliance for airfoil tonal noise reduction at various loading conditions". Physics of Fluids 34, n.º 4 (abril de 2022): 046113. http://dx.doi.org/10.1063/5.0087350.
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A novel concept of utilizing distributed surface compliance to achieve airfoil tonal noise reduction at various loading conditions is proposed. The aeroacoustics of airfoil configuration subjected to different loading conditions at angles of attack (AoAs) from 3° to 7° are numerically studied using high-fidelity two-dimensional direct aeroacoustic simulation at Reynolds and Mach numbers of [Formula: see text] and 0.4, respectively. Initially, airfoil configurations mounted with single elastic panel (SEP) at individual AoA are designed with the knowledge of respective rigid airfoil flow characteristics. Stemming from the analysis of noise reduction potential of SEP configurations using a reduced-order modeling approach, a distributed surface compliance (DSC) airfoil configuration utilizing three resonating panels is designed to attain airfoil tonal noise reduction over entire range of AoA. Comprehensive acoustic analyses establish that the DSC airfoil could provide a maximum noise reduction ranging from 3 to 7 dB without any sacrifice in airfoil aerodynamics. The extent of noise reduction with DSC airfoil is found dependent on the flow-induced modal responses of the panels. At lower AoA, the panel(s) resonate in their designed structural modes, which remarkably weaken the flow instabilities convecting over the airfoil suction surface and eventually airfoil noise radiation. At higher AoA, the panel responses deviate from their designed structural mode shapes but could still give less noise reduction. Therefore, the designed DSC airfoil shows a feasible concept for tonal noise reduction over a wide range of operational AoA, which substantiates its applicability for aerodynamic devices at low Reynolds numbers.
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Zhu, Chunli, Hassan Hemida, Dominic Flynn, Chris Baker, Xifeng Liang y Dan Zhou. "Numerical simulation of the slipstream and aeroacoustic field around a high-speed train". Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 231, n.º 6 (4 de abril de 2016): 740–56. http://dx.doi.org/10.1177/0954409716641150.
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The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.