Relevant bibliographies by topics / Acoustic liner, acoustic, aeroacoustic, noise reduction

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Conference papers

Academic literature on the topic 'Acoustic liner, acoustic, aeroacoustic, noise reduction'

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Published: 10 March 2023

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Journal articles on the topic "Acoustic liner, acoustic, aeroacoustic, noise reduction"

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Glover, Jennifer, and 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, no. 6 (August 1, 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, and 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, no. 7 (February 1, 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, and 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, no. 6 (August 1, 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, and Emad Uddin. "Development of a Linear Acoustic Array for Aero-Acoustic Quantification of Camber-Bladed Vertical Axis Wind Turbine." Sensors 20, no. 20 (October 21, 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, and Xiaofeng Sun. "Noise reduction by perforated cascades in annular ducts." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, no. 5 (February 1, 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, and Makoto Yokochi. "Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner." Advances in Acoustics and Vibration 2011 (September 20, 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, and Wenchao Huang. "Acoustic Experimental Technology for Aircraft Nacelle Liner." Aerospace 10, no. 1 (January 5, 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, and Jing Sun. "Computational Aeroacoustic Simulation of Landing Gear." Applied Mechanics and Materials 421 (September 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, no. 8 (November 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, and Paolo Castellini. "A comparison between aeroacoustic source mapping techniques for the characterisation of wind turbine blade models with microphone arrays." ACTA IMEKO 10, no. 4 (December 30, 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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Dissertations / Theses on the topic "Acoustic liner, acoustic, aeroacoustic, noise reduction"

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Pourreza, Atabak. "On the design, realization, and preliminary run of a novel grazing flow test rig for acoustic liners’ assessment under high temperature condition." Doctoral thesis, 2020. http://hdl.handle.net/2158/1198299.

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The installation of acoustic liners can represent an effective strategy for noise reduction in aero engines. The performance of an acoustic liner as a sound absorbing device is expressed by the acoustic impedance which mainly depends on its geometry and on the peculiar flow conditions acting on its surface. Several parameters are involved in the estimation of the impedance through a non-trivial dependence; this is even more complex when such devices are installed within a high-speed and high-temperature flow field such the one characteristic of the core nozzle of an aeroengine. Within such a scenario the experimental investigation is fundamental in order to assess the liner performance accurately. The most reliable way to determine the acoustic impedance is through a grazing flow rig which allows to experimentally investigate the acoustic liner performances under different flow conditions by using a controlled acoustic signal as excitation. At the Department of Industrial Engineering in Florence, a novel grazing flow rig for testing liners at flow conditions representative of the Low-Pressure Turbine (LPT) exit, i.e. at high speed and high temperature, has been designed and realized. The present work describes the design of the test rig and the preliminary experimental outcomes achieved for assessing the rig performances. The design of all the main components has been addressed following a comprehensive approach in order to meet the acoustic and aerodynamic requirements and by considering the thermo-structural effects as well. The design process has been supported by the use of Finite Element Analyses, the main results and the design solutions achieved are shown. As the rig is supposed to work under high temperature conditions, the sensors to be used for collecting the acoustic data shall withstand the hot flow as well. Hence, an experimental analysis has been carried out in order to compare the main market solutions available. As a result, the most suitable measurement device was identified. Once the design and the construction of the rig was finished, a preliminary set of tests was performed to prove the eligibility of the rig for the designed purpose. The uniformity of the flow field into the test section has been verified through a preliminary measurement of the flow profile. From the acoustic point of view, the reflection coefficient was measured at the duct ends and the results demonstrated very low reflections proving the effectiveness of the designed anechoic terminations. In addition, a first test on an acoustic liner sample was performed, i.e. the transmission loss was measured at cold flow condition. The overall results demonstrate that the rig is properly designed for the desired purposes.
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Books on the topic "Acoustic liner, acoustic, aeroacoustic, noise reduction"

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W, Premo John, Hersh Alan S, Langley Research Center, and United States. National Aeronautics and Space Administration., eds. Advanced turbofan duct liner concepts. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.

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Conference papers on the topic "Acoustic liner, acoustic, aeroacoustic, noise reduction"

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Yu, Jia, and Eugene Chien. "Folding Cavity Acoustic Liner For Combustion Noise Reduction." In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference). Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-2681.

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Sarigul-Klijn, Nesrin, Israel Lopez, and Seung-Il Baek. "Scaled Acoustics Experiments and Vibration Prediction Based Structural Health Monitoring." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68613.

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Vibration and acoustic-based health monitoring techniques are presented to monitor structural health under dynamic environment. In order to extract damage sensitive features, linear and nonlinear dimensional reduction techniques are applied and compared. First, a vibration numerical study based on the damage index method is used to provide both location and severity of impact damage. Next, controlled scaled experimental measurements are taken to investigate the aeroacoustic properties of sub-scale wings under known damage conditions. The aeroacoustic nature of the flow field in and around generic aircraft wing damage is determined to characterize the physical mechanism of noise generated by the damage and its applicability to battle damage detection. Simulated battle damage is investigated using a baseline, and two damage models introduced; namely, (1) an undamaged wing as baseline, (2) chordwise-spanwise-partial-penetration (SCPP), and (3) spanwise-chordwise-full-penetration (SCFP). Dimensional reduction techniques are employed to extract time-frequency domain features, which can be used to detect the presence of structural damage. Results are given to illustrate effectiveness of this approach.
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Zenz, Manuel, Loris Simonassi, Philipp Bruckner, Simon Pramstrahler, Franz Heitmeir, and Andreas Marn. "Noise Attenuation Potential Using Helmholtz Absorbers Integrated in Low Pressure Turbine Exit Guide Vanes and Turbine Exit Casing End Walls." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14233.

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Abstract To further reduce the noise emitted from modern aircrafts, every possibility has to be taken into account. Acoustic liners are successfully used in the inlet or the bypass duct of aircraft engines to mitigate the noise emitted by the fan. Due to the rough environment (high temperature, flow velocity, higher order duct modes), the exhaust duct is of limited use concerning the application of acoustic liners. It is well known that the last stage low pressure turbine (LPT) has a dominant influence onto the emitted noise of an aircraft engine especially at low load conditions such as approach. A noise reduction in this area could lead to a beneficial result of decreasing the noise content which is directly emitted in the environment. This paper is about noise attenuation using Helmholtz absorbers in various parts of a turbine exit casing (TEC). These single degree of freedom absorbers have been integrated in turbine exit guide vanes (TEGVs), with the openings on the vanes suction side, as well as in the inner and outer duct end walls. Different absorber neck diameters were investigated and combined with different vane designs. The vane designs studied included a state of the art set-up as well as vanes with a lean. Test runs were performed with altered combinations of vanes and end walls under engine relevant operating conditions in a subsonic test turbine facility for aerodynamic, aeroacoustic and aeroelastic investigations (STTF-AAAI) located at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. Comparisons between all these setups and the respective hard wall reference cases were done. The resulting sound pressure levels as well as sound power levels of all investigated combinations are listed and compared concerning each configurations noise attenuation potential. Additionally, the flow field downstream of every setup is analysed if the aerodynamic behaviour is changing. The investigated operating point is the noise certification point Approach (APP) which is of high importance because of the high acoustical impact onto the environment around airports during the landing procedure of an aircraft. The acoustical data has been obtained by using flush mounted condenser microphones located downstream of the TEC. The whole test section was rotated over 360 deg around the flow channel. To detect if the aerodynamical behaviour changes by including openings into the flow channel end walls as well as into the vanes, aerodynamic measurements have been performed downstream of the TEC. The aerodynamical data was obtained by using an aerodynamic five-hole-probe (5HP) as well as a trailing edge probe.
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Mechefske, Chris K. "Acoustic Noise Reduction Liner for a 4T MRI Scanner." In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84245.

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High-field, high-speed Magnetic Resonance Imaging (MRI) can generate high levels of acoustic noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 Tesla MRI scanner under a variety of conditions. These measurement results show; 1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner, and 2) the true noise levels that are experienced by patients during echo planer imaging (EPI).
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Murugesan, Ramesh, and Vijayanandh Raja. "Acoustic Investigation on Unmanned Aerial Vehicle’s Rotor Using CFD-MRF Approach." In ASME 2019 Gas Turbine India Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gtindia2019-2430.

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Abstract Future developments have been indicated for further research and development in the Aeroacoustics of the components of Unmanned Aerial Vehicles (UAVs). In which the implementation of multi-rotor UAVs in the complex applications is quite high but it has the drawback of high drive-line noise levels, which is one of the prime radar detectability factors. As a result, an idea is emerged to design and test the quite UAV, in which the noise from propellers plays a major role. in order to the successful completion of the design study, a complete is conducted, in which the design parameters and various noise reduction methodologies in the rotating components have been noted and included in the final design. To minimize the noise signature issue in UAV, the idea finalized that to minimize the decibel of small Unmanned Aircraft System (UAS) propellers via leading-edge modifications. A computer-aided design of base propeller and three different versions propeller with leading-edge modifications are generated with the help of CATIA for Computational Fluid Dynamics (CFD) simulations. Comparative noise variation simulations between the existing and the propellers with modification are performed, in which dynamic conditions play a predominant to initiate the analysis and thereby the analyses are carried out with the help of ANSYS Workbench Fluent 16.2. Especially, to make an acceptable solution, the Moving Reference Frame (MRF) approach is used in order to capture the propeller rotation in an effective manner. Finally, a propeller with airfoil cut at the leading edge has induced the low noise.
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Perrino, Michael, Jeffrey Kastner, Ephraim Gutmark, and Sivaram Gogineni. "Towards Development of an Active Single-Layer Acoustic Liner for Jet Engine Noise Reduction." In 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2010. http://dx.doi.org/10.2514/6.2010-655.

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Rajput, Pankaj, and Sunil Kumar. "Directional Noise Reduction via Asymmetric Downstream Fluidic Injection." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71258.

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The main aim of this investigation is to analyze directional noise reduction resulting from asymmetric high momentum fluidic injection downstream of a Mach 0.9 nozzle. Jet noise has been identified as one of the primary obstacles to increasing commercial aviation capacity. Microjets in cross flow are known to enhance turbulent mixing in the shear layer due to the induced stream-wise vortices. This enhanced mixing can be used for reorganizing the spatial distribution of acoustic energy. Targeted reduction in the downward-emitted turbulent mixing noise can be achieved by strategically injecting high momentum fluid downstream of the jet exhaust. Detailed Large Eddy Simulations were performed on a hybrid block structured-unstructured mesh to generate the flow field which was then used for near field and far field noise computation. Aeroacoustic analogy based formulation was used for computing far-field noise estimation. Benchmark cases were validated with preexisting experimental data sets. Mean flow measurements suggest shorter jet core lengths due to the enhanced mixing resulting from fluidic injection. The induced asymmetry due to the fluidic injection gives rise to an asymmetric acoustic field leading to targeted directional noise reduction in the far field as measured by pressure probes.
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Kinzie, Kevin W., and James E. Bridges. "Jet Aeroacoustic Research at NASA (Keynote Paper)." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45052.

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An overview of NASA’s jet aeroacoustic research is provided here along with a description of NASA’s current and recent focused aircraft acoustic programs. These programs are designed to advance jet noise reduction technology through a balanced investigation of jet noise reduction concepts, understanding the fundamentals of jet flows and turbulence, and developing physics-based tools that predict jet flowfields and associated noise. Jet noise goals for these programs are highlighted with examples of key jet noise technologies.
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Mileshin, Victor I., Michael A. Nyukhtikov, Igor K. Orekhov, Sergey V. Pankov, and Sergey K. Shchipin. "Open Counter-Rotation Fan Blades Optimization Based on 3D Inverse Problem Navier-Stokes Solution Method With the Aim of Tonal Noise Reduction." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-51173.

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When developing counter-rotating fans for advanced new-generation aeroengines with unducted blades it is very important to provide high acoustic and aerodynamic characteristics [1]. This paper presents some results of gasdynamic and aeroacoustic optimization of unducted CRF blade profile by using 3D viscous inverse problem. Flow in unducted CRF on the basis of unsteady 3D Navier-Stokes equations is modeled at the 1st stage of designing in order to find the key tonal noise sources. Based on these results, it is found that one of the key tonal noise sources is Rotor 1 - Rotor 2 tip vortices interaction and potential rotor interaction. Then, using 3D solver of the viscous inverse problem, aerodynamic loads are redistributed along R1 and R2 blade height aiming at a decrease in tip vortex intensity and potential rotor interaction with a probable increase in the CRF thrust. To verify the aerodynamic characteristics of the modified CRF, steady flow calculations are carried out with the help of 3D Navier-Stokes equations and “mixing plane” interfaces. To verify the acoustic characteristics of the modified CRF, tonal noise modeling is carried out for original and modified CRFs using aeroacoustic CIAM’s 3DAS solver for solution of unsteady inviscid equations for disturbances. Ffowcs–Williams, Howkings approach is used for acoustic calculations in the far field. The near acoustic field and directivity diagrams in the far field are found. Using 3D inverse problem, the fan tonal noise is decreased by 4 dB for take-0ff and landing with no thrust and efficiency losses.
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Velarde-Sua´rez, Sandra, Rafael Ballesteros-Tajadura, Carlos Santolaria-Morros, and Bruno Pereiras-Garci´a. "Reduction of the Aerodynamic Tonal Noise of a Forward-Curved Centrifugal Fan by Modification of the Volute Tongue Geometry." In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77436.

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In this work, an experimental study about the influence of some geometric features on the aeroacoustic behavior of a squirrel-cage fan, used in automotive air conditioning units, has been carried out. The study focused on the effect of both the shape and the position of the volute tongue on the noise generated by the fan. Different geometric configurations were tested in order to compare the results. First of all, the performance curves were measured in a standardized test facility. Then, the acoustic behavior of the fan was characterized by means of acoustic pressure measurements near the fan inlet. The comparison of the test results indicated a great dependence of both the shape and the position of the volute tongue and the noise generation. In particular, some geometric configurations of the volute tongue were able to reduce the fan noise generation without reducing the fan performance.
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