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1
Kingan, Michael Joseph. "Aeroacoustic noise produced by an aerofoil." Thesis, University of Canterbury. Mechanical Engineering, 2005. http://hdl.handle.net/10092/6596.
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This thesis describes an investigation into the aeroacoustic noise produced by an aerofoil
using experimental, computational and theoretical methods. Several different types of
aeroacoustic noise generation mechanisms and the parameters which affect these
mechanisms were identified and investigated.
The aerofoils used' in this investigation all had chord lengths of 100mm and had a
maximum thickness between 18mm and 30mm. Experimental testing was undertaken in
the low noise wind tunnel in the Department of Mechanical Engineering at the University
of Canterbury with the aerofoils mounted at the exit of the tunnel. Airflow speeds from
10m/s to 40m/s and a range of angles of incidence were investigated. A number of
modifications were made to reduce the noise and improve the operation of the wind
tunnel. Different methods of measuring the aeroacoustic noise produced by an aerofoil
were also investigated.
The theory of aeroacoustic noise generation is described and the effect of a scattering
surface on the efficiency of these aeroacoustic noise sources was investigated. A number
of different mechanisms by which an aerofoil produces aeroacoustic noise were
identified. These mechanisms were divided into three main categories: (1) blunt trailing
edge aerofoil noise (2) sharp trailing edge aerofoil noise and (3) stalled aerofoil noise.
The effect of air temperature on the production of aeroacoustic noise was also
investigated. It was found that in most instances air temperature would have little effect
on aeroacoustic noise generation.
An extensive study of the aeroacoustic noise produced by a number of different aerofoils
was undertaken. Modelling of the airflow over the aerofoils was used to determine the
mechanism by which aeroacoustic noise is produced. Several different aeroacoustic noise
generation mechanisms were identified. Theoretical models were also used to model the
aeroacoustic noise produced by the aerofoils.
Several treatments to reduce the level of aeroacoustic noise produced by an aerofoil were
investigated. The treatments reduced the aeroacoustic noise produced by an aerofoil with
varying degrees of success.
A method for measuring the aeroacoustic noise produced by car roof racks mounted on
the roof of a vehicle using a relatively small wind tunnel was established. The noise level
produced by a roof rack installed 011 the roof of a vehicle measured using this technique
compared favourably with measurements made on a full vehicle in a large wind tunnel.
The method shows promise as a low cost method of accurately measuring the
aeroacoustic noise produced by roof racks installed on a vehicle roof.
2
Boorsma, Koen. "Aeroacoustic control of landing gear noise using perforated fairings." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/66081/.
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A study was performed to investigate and optimize the application of perforated fairings for landing gear noise control. The sparse knowledge about this new subject has necessitated a more fundamental study involving a basic fairing-strut configuration, followed by wind tunnel tests on a simplified landing gear configuration incorporating perforated fairings. For the basic configuration, various exchangeable perforated half-cylindrical shells shrouding a circular cylinder were the subject of aerodynamic and acoustic tests. A qualitative and quantitative description has been given of the influence of perforated fairings on time averaged and unsteady flow and the related acoustics. The bled air through the shell prevents the formation of large scale vortices associated with the shell and thereby reduces low frequency noise. However, a test with a noisy H-beam replacing the circular cylinder has indicated that increasing porosity can result in adverse noise effects due to the bled mass flow washing the strut. Shearing flow past the perforate has been shown to create adverse self-noise of which both intensity and spectral content are dictated by the local velocity past the perforate. The application of perforated fairings to the simplified landing gear model reduces the low frequency noise introduced by the solid fairings to values below the baseline landing gear configuration in both side and ground view directions. Exposing the perforate outside the stagnation area does not yield extra noise reduction but introduces perforate self-noise. The synthesis of the conducted studies has shed new light on the application of perforated fairings for landing gear noise control. In particular the effects of porosity and perforation location have been clarified. However more research is needed for further optimization of these parameters.
3
Yardibi, Tarik. "Source localization and power estimation in aeroacoustic noise measurements." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024868.
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Gea-Aguilera, Fernando. "Aerodynamic and aeroacoustic modelling of engine fan broadband noise." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/412640/.
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This thesis investigates simplified but representative configurations of the fan wake-OGV interaction noise, which is a major source of engine fan broadband noise during take-off and landing. To this end, Computational AeroAcoustics (CAA) simulations are performed by using the Linearised Euler Equations (LEEs) and synthetic turbulence methods. An advanced digital filter method is presented to generate divergence-free synthetic turbulence with explicit control on the resulting turbulence spectrum. The method, which is based on the Random Particle-Mesh (RPM) method and synthetic eddy methods, is able to produce two- and three-dimensional fluctuating velocity fields of homogeneous isotropic and anisotropic turbulence. It is also shown that similar levels of simulation accuracy can be achieved by using digital filter and Fourier mode methods. Nevertheless, the advanced digital filter method provides enhanced performance in terms of computational cost (up to 3:9 times faster for two-dimensional simulations in this study). CAA simulations using the advanced digital filter method are performed to improve current understanding of leading edge noise from single aerofoils. For example, the method is used to examine the distortion of turbulent structures in the leading edge region. Furthermore, a comparison between numerical and experimental noise measurements in open-jet wind tunnel experiments indicate that the advanced digital filter method is capable of reproducing experimental results with an accuracy to within 3 dB. This thesis also presents a parameter study to assess the effects of moderately anisotropic turbulence, as occurs in the fan wakes, on leading edge noise from single aerofoils. Finally, fan wake modelling assumptions, such as cyclostationary variations in turbulent kinetic energy and integral length scale, are investigated using a cascade of thin aerofoils. Results indicate that broadband noise mainly depends on the circumferentially-averaged spectrum that is perceived by the cascade, and not on the instantaneous features of the fan wakes. A parameter study on cascade noise using isotropic turbulence is also included in this thesis, where variations in the vane count, aerofoil thickness, camber, mean flow Mach number, stagger angle, and inter-vane spacing are investigated. It is confirmed that the flat plate assumption provides sufficient accuracy for the frequency range in which engine fan broadband noise is relevant.
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Kiran, Amit. "Jet noise : aeroacoustic distribution of a subsonic co-axial jet." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/3914/.
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The noise generated by aircraft can be easily heard by those living under the flight path of passenger or cargo carriers. It is considered an environmental pollutant and is treated as such by the International Civil Aviation Organization (ICAO) who monitor and review noise levels. The ICAO imposes substantial fines on those carriers who do not adhere to the decibel limitations. With the new limit or `stage' enforced in 2006, aircraft manufacturers (including jet engine manufacturers) are seeking ways to reduce the noise created by an aircraft. A 1/150th scale model, based on the exit geometry typically found on commercial jet engines, was designed and manufactured at Warwick. The laboratory jet flow conditions operated at 0.7 Mach. The work presented in this thesis looks at the noise generated in a subsonic, co- owing jet, with particular focus given to the distribution sound sources from 5 kHz to 80 kHz (0.375 St to 6.0 St). An acoustic mirror mounted on a motorized 3-way traverse measured radiated sound in the co-flowing jet to produce 2D sound source maps. This is done using combinations of smooth cowl and chevrons for the core and bypass nozzles. For frequencies less than 30 kHz, a reduction of noise was observed using the bypass chevron nozzle compared with the bypass smooth cowl nozzle. Laser Doppler Anemometry (LDA) was used to reveal the 2D flow dynamics of the jet, supporting the acoustic distribution results with velocity profiles of the flow. The change in the flow dynamics with different nozzle combinations is discussed and different regions of the flow were identified.
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Ghadiani, Ali. "Aerodynamics and aeroacoustic of sail masts." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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In this thesis, the turbulent flow induced by sail masts is simulated using compressible k-w SST detached eddy simulation (DES). The mast is investigated in two different yaw angles at 0 and 90 and the predetermined condition is V = 20 m/s to find the main broadband and tonal noise sources. And then the same cases are compared to simple shape of sail mast without internal cavities. The purpose of this work is to investigate whether the cases generate tonal noise when winds past the sail mast. Another objective is to study aerodynamic parameters around the four cases. The influence of the mast tips is assessed and the Sound Pressure Levels (SPL) that are gotten from pressure fluctuations are shown at the end to find the tonal noise and show the study cases with a cavity inside make much more noise than simplified sail mast. By looking at the peaks in the sound pressure level (SPL) the tonal noise at specific frequencies can be found.
The commercial software STAR-CCM+ was used for all three parts pre-processing, running simulations, and post-processing to understand the noise generation and aerodynamic features.
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Yu, Chao. "An acoustic intensity-based method and its aeroacoustic applications." Diss., Connect to online resource - MSU authorized users, 2008.
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Pignier, Nicolas. "Sound propagation from sustainable ground vehicles : from aeroacoustic sources to urban noise." Licentiate thesis, KTH, Farkost och flyg, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174182.
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Transportation is the main source of environmental noise in Europe, with an estimated 125 million people affected by excessive noise levels from road traffic, causing a burden of noise related diseases and having a substantial economic impact on society. In order to reduce exposure to high levels of traffic noise, two approaches are the topic of extensive research: preventing sound from propagating from roads and railways using for example noise barriers, and reducing the sources of noise themselves. The second solution, which addresses directly the cause of the problem, requires improved design methods, with a more systematic resort to multi-functional design. Addressing cross-functions simultaneously reduces the number of design iterations and the high cost of prototyping. The work presented in this thesis aims at developing methods that can be used to design quieter vehicle concepts within a multi-functional approach, and is articulated around two main axis of research, aerodynamic sound generation and sound propagation. The first axis aims at performing an aeroacoustic analysis to predict aerodynamic sound sources. A hybrid method is used on the example of a type of submerged air inlet called a NACA duct, where the near-field flow is solved through detached eddy simulation (DES) and where the far-field acoustics is computed using the Ffowcs Williams and Hawkings integral. Results for the flow for various operating conditions are presented and validated against experimental data from the literature, with very good agreement. Far-field acoustic results are shown, exhibiting levels and components that are strongly dependent on the operating conditions. This analysis gives a framework for future aeroacoustic analysis in the project, and sets the path for the development of air inlets with improved aerodynamic and aeroacoustic characteristics. The second axis focuses on the propagation of sound from a given source, moving in an urban environment. An approximate boundary method is presented, which relies on the Kirchhoff approximation applied to the Kirchhoff-Helmholtz integral equation. Using this approximation speeds up the computational time compared to using a regular boundary element method. The resulting expression is extended to account for multiple scattering through consecutive updates of the surface pressures, and for moving sources through the introduction of a retarded time and of a Doppler shift. Validation tests for this method are presented, from simple scatterers to a more realistic configuration, showing good agreement with analytical, experimental and simulated work.<br>Fordon är den främsta källan till bullerexponering i Europa med uppskattningsvis 125 miljoner människor som är utsatta för höga ljudnivåer från vägtrafik, vilket kan orsaka bullerrelaterade häsloproblem samt har en betydande ekonomisk effekt på samhället. För att minska exponeringen för höga ljudnivåer från fordon, finns det två angreppssätt som båda idag är ämne för omfattande forskning: att förhindra ljudutbredning från vägar och järnvägar (till exempel med hjälp av bullerskydd), samt att minska ljudnivån från olika bullerkällor. Den sistnämnda, som direkt riktar sig till problemets orsak, kräver förbättrade designmetoder med mer systematisk användning av multifunktionell design. Att hantera flera funktioner hos fordonet samtidigt minskar antalet designiterationer och den höga kostnaden för prototyper. Arbetet som presenteras i denna avhandling syftar till att utveckla metoder som kan användas för att utforma tystare fordonskoncept inom ramen för en multifunktionell strategi och fokuserar på två spår i forskningen: aerodynamisk ljudalstring och ljudutbredning från rörliga källor. Det första spåret i forskningen syftar till att utföra en aeroakustisk undersökning för att modellera aerodynamiska ljudkällor. En hybridmetod tillämpas på ett typ av nedsänkt luftintag, kallat NACA-intag, där källområdet i strömningen löses genom detached eddy simulation (DES) och akustiken i fjärrfältet beräknas enligt Ffowcs Williams och Hawkings integral. Resultat för strömningen för olika driftförhållanden presenteras och valideras mot experimentella data från litteraturen, med mycket god överensstämmelse. Resultat för det akustika fjärrfältet visas, vilket uppvisar nivåer och komponenter som är starkt beroende av driftförhållandena. Denna analys ger en ram för kommande analyser av aeroakustik inom projektet och visar vägen för utvecklingen av luftintag med förbättrade aerodynamiska och aeroakustika egenskaper. Det andra spåret i forskningsprojektet är inriktat på ljudets utbredning från en given källa som rör sig i en urban miljö. En approximativ randvärdesmetod presenteras som bygger på Kirchhoff approximation tillämpad på Kirchhoff-Helmholtz integralekvation. Med hjälp av denna approximation minskas beräkningstiden jämfort med vanlig boundary element method (BEM). Modellen utvecklas sedan för att kunna hantera flera reflektioner genom att det akustiska trycket på ytorna uppdateras för varje reflektion samt för att kunna hantera rörliga källor genom att introducera tidsfördröjningar och Dopplerförskjutning. Validering för denna modell presenteras, från enkla spridare till en mer realistisk urban konfiguration, som visar god överensstämmelse med analytiskt, experimentellt och simulerat data.<br><p>QC 20151002</p>
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Nance, Douglas Vinson. "Finite volume schemes optimized for low numerical dispersion and their aeroacoustic applications." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12110.
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Leitch, Thomas A. "Reduction of Unsteady Rotor-Stator Interaction Using Trailing Edge Blowing." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/30527.
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An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of four stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform. In these experiments a reduced number of stators (four) was used in a 1/14 scale model inlet which was coupled to a 4.1 in (10.4 cm) turbofan engine simulator with 18 rotors and 26 downstream stators. This study is a preliminary step toward a more in depth investigation of using trailing edge blowing to reduce unsteady rotor-stator interaction. Steady-state measurements of the aerodynamic flow field and acoustic far field were made in order to evaluate the aeroacoustic performance at three simulator speeds: 40%, 60%, and 88% of the design speed. The lowest test speed of 40% design speed showed the most dramatic reduction in radiated noise. Noise reductions as large as 8.9 dB in the blade passing tone were recorded at 40% design speed, while a tone reduction of 5.5 dB was recorded at 60% design speed. At 88% design speed a maximum tone reduction of 2.6 dB was recorded. In addition, trailing edge blowing reduced the overall sound pressure level in every case. For both the 40% design speed and the 60% design speed, the fan face distortion was significantly reduced due to the trailing edge blowing. The addition of trailing edge blowing from the four upstream stators did not change the total pressure ratio, and the mass flow added by the blowing was approximately 1%. The results of these experiments clearly demonstrate that blowing from the trailing edges of the stators is effective in reducing unsteady rotor-stator interaction and the subsequent forward radiated noise.<br>Master of Science
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Remillieux, Marcel Christophe. "Aeroacoustic Study of a Model-Scale Landing Gear in a Semi-Anechoic Wind Tunnel." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31674.
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An aeroacoustic study was conducted on a 26%-scale Boeing 777 main landing gear in the Virginia Tech (VT) Anechoic Stability Wind Tunnel. The VT Anechoic Stability Wind Tunnel allowed noise measurements to be carried out using both a 63-elements microphone phased array and a linear array of 15 microphones. The noise sources were identified from the flyover view under various flow speeds and the phased array positioned in both the near and far-field. The directivity pattern of the landing gear was determined using the linear array of microphones. The effectiveness of 4 passive noise control devices was evaluated. The 26%-scale model tested was a faithful reproduction of the full-scale landing gear and included most of the full-scale details with accuracy down to 3 mm. The same landing gear model was previously tested in the original hard-walled configuration of the VT tunnel with the same phased array mounted on the wall of the test section, i.e. near-field position. Thus, the new anechoic configuration of the VT wind tunnel offered a unique opportunity to directly compare, using the same gear model and phased array instrumentation, data collected in hard-walled and semi-anechoic test sections.
The main objectives of the present work were (i) to evaluate the validity of conducting aeroacoustic studies in non-acoustically treated, hard-walled wind tunnels, (ii) to test the effectiveness of various streamlining devices (passive noise control) at different flyover locations, and (iii) to assess if phased array measurements can be used to estimate noise reduction.
As expected, the results from this work show that a reduction of the background noise (e.g. anechoic configuration) leads to significantly cleaner beamforming maps and allows one to locate noise sources that would not be identified otherwise. By using the integrated spectra for the baseline landing gear, it was found that in the hard-walled test section the levels of the landing gear noise were overestimated.
Phased array measurements in the near and far-field positions were also compared in the anechoic configuration. The results showed that straight under the gear, near-field measurements located only the lower-truck noise sources, i.e. noise components located behind the truck were shielded. It was thus demonstrated that near-field, phased-array measurements of the landing gear noise straight under the gear are not suitable. The array was also placed in the far-field, on the rear-arc of the landing gear. From this position, other noise sources such as the strut could be identified. This result demonstrated that noise from the landing gear on the flyover path cannot be characterized by only taking phased array measurement right under the gear.
The noise reduction potential of various streamlining devices was estimated from phased array measurements (by integrating the beamforming maps) and using the linear array of individually calibrated microphones. Comparison of the two approaches showed that the reductions estimated from the phased array and a single microphone were in good agreement in the far-field. However, it was found that in the near-field, straight under the gear, phased array measurements greatly overestimate the attenuation.<br>Master of Science
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Kuhn, Thomas [Verfasser]. "Quantification of Uncertainty in Aeroacoustic Cavity Noise Simulations with a Discontinuous Galerkin Solver / Thomas Kuhn." München : Verlag Dr. Hut, 2021. http://d-nb.info/1238422926/34.
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Zavala, Paulo Alexandre Galarce. "Identificação de fontes aeroacústicas e fontes em movimento = Aeroacoustic source and moving source identification." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265357.
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Orientador: José Roberto de França Arruda<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-20T09:40:59Z (GMT). No. of bitstreams: 1
Zavala_PauloAlexandreGalarce_D.pdf: 48986854 bytes, checksum: a4b9853c4e0f7957b591afad2a9d4974 (MD5)
Previous issue date: 2012<br>Resumo: Identificação de fontes acústicas é uma ferramenta de análise importante para as melhorias mecânicas necessárias para o atendimento de normas de ruído restritivas, em especial em duas áreas: engenharia de aeronaves e engenharia de veículos. Esses dois setores têm de cumprir com as normas de sobre-vôo de aeroportos e ruído de passagem, respectivamente. Este trabalho tem o objetivo de desenvolver um método de identificação para problemas de fontes aeroacústicas e fontes em movimento. O método baseado no beamforming inverso generalizado tem a vantagem de localizar fontes distribuídas e multipólos e é usado neste trabalho. A estratégia é a de se realizarem verificações em casos simples, com simulações e avaliações experimentais. No teste aeroacústico inicial, um cilindro sob fluxo subsônico, os eventos dominantes de ruído são analisados, e o centro do dipólo e sua orientação são identificados. No teste seguinte, duas-estruturas sob fluxo subsônico, o método híbrido e o mapeamento híbrido inverso generalizado, ambos propostos neste trabalho, permitem uma comparação direta dos níveis de mapeamento com os resultados de beamforming convencional, e uma atenuação das auto-potências da matriz de espectros cruzados é usada para melhorar a resolução. Na identificação de dipólos, uma grade 3D é usada, e a orientação do dipolo é identificada com um componente em direção à malha de microphones, o que é possível devido à utilização de um re-escalonamento da matriz de transferência. Avaliações de diretividade para as distribuições de dipólo são realizadas e comparadas com microfones de campo-distante. No terceiro caso aeroacústico, o aerofólio NACA-0012 sob fluxo subsônico, identificações de monopólos são comparados com resultados da literatura obtidos com o DAMAS2. Para os estudos de identificação de fonte em movimento, duas medições são realizadas: ruído de passagem de um veículo de passageiros, e ruído de passagem de caminhão. A de-Dopplerização baseada no centro da grade é adotada, e dois artifícios são desenvolvidos: uso de imagem de fonte na função de transferência; e compensação de foco para fonte de radiação não-esférica. A malha de microfones tem um arranjo especial para melhor resolução horizontal em frequências baixas. Mapeamentos com a contribuição no nível de ruído de passagem são utilizados nas verificações efetuadas de 50Hz a 7kHz, utilizando dois alto-falantes com radiação de ruído tonal e com ruído de banda larga. No final, o desempenho global do método beamforming inverso generalizado é discutido, apresentando suas vantagens, e.g. detecção de fonte multipólo, e suas desvantagens, e.g. sensibilidade a fontes estranhas<br>Abstract: Identification of acoustic sources is an important analysis tool for the mechanical design improvements required to compliance with restrictive noise regulations, specially on two areas: aircraft and vehicle engineering. These two industries have to comply with the airplane fly-over noise and vehicle pass-by noise limits, respectively. This thesis has the objective to develop an identification method for aeroacoustic and moving source problems. The method based on the generalized inverse beamforming has the advantage to locate distributed sources of multipole type of radiation and is used in this thesis. The strategy is to perform verifications on simple cases, with simulations and experimental assessments. On the aeroacoustic initial testing, with a cylinder under subsonic flow, peak noise events are analyzed, and the dipole center and orientation are identified. In the following test case, two-structures in subsonic flow, the Hybrid Method and the Hybrid Generalized Inverse Mapping, both proposed in this work, allow a direct comparison of mapping levels to the conventional beamforming results, and an attenuation of the auto-powers in the cross-spectral matrix is used to improve resolution. For dipole identification, a 3D grid is used, and its orientation is identified with a component towards array, which is possible due to the use of a transfer matrix re-scaling. Directivity assessments are performed for dipole distributions and compared to far-field microphones. In the third aeroacoustic case, NACA-0012 airfoil under subsonic flow, monopole identifications are compared to DAMAS2 results from the literature. On moving source identification, two measurements are performed: passenger vehicle pass-by noise; and truck pass-by noise test. The de-Dopplerization based on grid center is adopted, and two artifices are developed: image source in transfer function; and focus compensation for source non-spherical radiation. The microphone array has a special design for improved low frequency horizontal resolution. Pass-by noise level contribution mappings are used on verifications performed from 50Hz to 7kHz using two loudspeakers with tonal and broadband noise radiation. Finally, overall performance of the generalized inverse beamforming method is discussed, presenting its advantages, e.g. multipole source detection, and limitations, e.g. sensitivity to extraneous sources<br>Doutorado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Doutor em Engenharia Mecânica
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Allampalli, Vasanth. "Fourth order Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme for NASA Glenn Research Center's Broadband Aeroacoustic Stator Simulation (BASS) Code." Toledo, Ohio : University of Toledo, 2010. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1270739741.
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Dissertation (Ph.D.)--University of Toledo, 2010.<br>Typescript. "Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering." "A dissertation entitled"--at head of title. Title from title page of PDF document. Bibliography: p. 152-156.
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Scheit, Christoph [Verfasser]. "Hybrid Aeroacoustic Methods for Broadband Noise Calculation : Hybride aeroakustische Verfahren zur Berechnung von Breitbandlärm / Christoph Scheit." Aachen : Shaker, 2016. http://d-nb.info/1120864372/34.
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Werner, Maike [Verfasser]. "Experimental Study on Tonal Self-Noise Generation by Aeroacoustic Feedback on a Side Mirror / Maike Werner." München : Verlag Dr. Hut, 2018. http://d-nb.info/1164293540/34.
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Erbig, Lars [Verfasser], and Claus-Dieter [Akademischer Betreuer] Munz. "Aeroacoustic simulation of turbulent boundary layer induced automotive gap noise / Lars Erbig ; Betreuer: Claus-Dieter Munz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2021. http://d-nb.info/122792786X/34.
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Tang, Kefan. "Numerical simulation of flow induced noise by means of the hybrid method with LES and aeroacoustic analogy." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972838066.
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Tautz, Matthias [Verfasser], Stefan [Akademischer Betreuer] Becker, Stefan [Gutachter] Becker, and Manfred [Gutachter] Kaltenbacher. "Aeroacoustic Noise Prediction of Automotive HVAC Systems / Matthias Tautz ; Gutachter: Stefan Becker, Manfred Kaltenbacher ; Betreuer: Stefan Becker." Erlangen : FAU University Press, 2019. http://d-nb.info/1191480828/34.
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Swanson, Elizabeth. "An investigation into the use of aeroacoustic jet noise theory in the interpretation of volcanic infrasound signals." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682351.
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Researchers in volcanic infrasound have proposed links between the acoustic signals of industrial jets and those recorded during sustained plume-generating volcanic eruptions (Matoza et aI., 2009; Fee et aI., 201Ob). If valid, this link offers a scaling law between the peak frequency of the volcanic signal and the exit velocity, a key parameter in determining the behaviour of eruption columns and predicting the dispersal of volcanic products. This PhD explores the validity and practicality of applying the engineering aeroacoustic results to volcanology through laboratory experiments with a range of nozzle geometries and a field case study. PIV analysis of a series of laboratory jet experiments demonstrated significant differences between the near to intermediate fields (NIP) of jets exiting from convergent nozzles, such as those commonly reported in the engineering literature, and those exiting from straight and divergent nozzles. As the NIP is the main region for sound generation, changes in its flow have implications for jet noise generation. Spectral analysis and adaptive beamforming of the acoustic signals of these jet flows showed them to be dominated by internal noise sources. Though the identification of differing noise sources was achieved, retrieval of the jet operating conditions via the standard empirical spectra was not possible. These results have important implications for the interpretation of infrasonic signals from sustained volcanic eruptions. The complex non-convergent geometry and large diameter of volcanic vents mean that high levels of internal volcanic noise are expected in infrasound from sustained explosive volcanic eruptions; As a substantial component of infrasound generated by a sustained eruption might not be from the plume itself, it is important to separate generation regions of different sources before inferring source parameters from infrasound data. Such separation requires a good understanding of the propagation path. Results from a multi-array field study at Sakurajima volcano, Japan, demonstrated the influence of local topography on the recorded infrasound signals. These influences require robust modelling before the vertical location of volcanic infrasound signals can be identified. This thesis serves as a reminder of the infancy of the infrasonic monitoring in terms of sustained events and identifies key goals for future laboratory experiments.
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Cheung, Lawrence C. "Aeroacoustic noise prediction and the dynamics of shear layers and jets using the nonlinear parabolized stability equations /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Kapa, Lilla. "Numerical prediction of noise production and propagation." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209828.
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Numerical simulation of noise production and propagation is a very complex problem. A methodology fitting for one particular problem can fail for another one. So there are no general guidelines on how to deal with such phenomena. In the present work, noise propagated in non-uniform mean-flow is considered. For most cases, in the propagation field, there is a rather significant region where the mean flow is not uniform, but the sound production is negligible compared to the noise emitted by the source region. In this<p>nearfield, a linear set of propagation equations may be considered (LEE). For such problems, the following simulation methodology is proposed:<p>1. Incompressible/compressible LES simulation in the source region.<p>2. Linearized Euler Equations to propagate the noise through the nonlinear mean flow.<p>3. Kirchhoff method in the farfield, if necessary.<p>This thesis deals with the second item of this system (LEE), including interfacing with the other two steps.<br>Doctorat en Sciences de l'ingénieur<br>info:eu-repo/semantics/nonPublished
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Schenk, Austin R. "Computational Investigation of the Effects of Rotor-on-Rotor Interactions on Thrust and Noise." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8611.
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Recent advancements in electric propulsion systems have made electric vertical takeoff and landing aircraft a reality, and one that is seen as a partial solution to the growing issue of urban traffic congestion. Designing an aircraft with multiple smaller motors and rotors spread across the wings–referred to as distributed electric propulsion (DEP)–has shown great potential in help- ing improve electric aircraft performance by offering increased propulsive efficiency, augmented lift, and structural load distribution. For these reasons, DEP is one configuration that is currently being implemented into multiple prototype designs (e.g. NASA’s Maxwell X-57, Airbus Vahana, Opener BlackFly, and Joby S2). However, while a DEP configuration has many potential benefits, it complicates the aerodynamics by introducing complex rotor-on-rotor interactions which can significantly affect noise generation. In this study we use unsteady Reynolds-averaged Navier–Stokes (RANS) simulations (STAR-CCM+) with an aeroacoustic solver (PSU-WOPWOP) to quantify thrust fluctuations and noise generation for two distinct rotor-rotor configurations. The configurations investigated in this study are: 1) coplanar rotors with a varying tip separation distance and 2) one rotor downstream of the other at varying distances for a fixed tip separation distance. Both configurations are investigated using an APC 10x7E and DJI-based 0.24 m rotor. It was found that tip-to-tip separation distance has a stronger influence on noise generation than the downstream separation distance does. A one diameter change in tip separation distance resulted in a ∼15 dBA change in noise while a three diameter change in downstream separation distance only resulted in a ∼9 dBA change in noise for the same rotor. Changes in thrust fluctuations were found to predict trends in noise generation well for multi-rotor configurations. Additionally, it was shown that when rotors are located less than 10% of the diameter apart from each other, noise can be decreased by up to 9 dBA by moving one rotor ∼0.5 diameter downstream of the other.
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Matouk, Rabea. "Calculation of Aerodynamic Noise of Wing Airfoils by Hybrid Methods." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/240641.
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This research is situated in the field of Computational AeroAcoustics (CAA). The thesis focuses on the computation of the aerodynamic noise generated by turbulent flows around wing, fan, or propeller airfoils. The computation of the noise radiated from a device is the first step for designers to understand the acoustical characteristics and to determine the noise sources in order to modify the design toward having acoustically efficient products. As a case study, the broadband or trailing-edge noise emanating from a CD (Controlled-Diffusion) airfoil, belonging to a fan is studied. The hybrid methods of aeroacoustic are applied to simulate and predict the radiated noise. The necessary tools were researched and developed. The hybrid methods consist in two steps simulations, where the determination of the aerodynamic field is decoupled from the computation of the acoustic waves propagation to the far field, so the first part of this thesis is devoted to an aerodynamic study of the considered airfoil. In this part of the thesis, a complete aerodynamic study has been performed. Some aspects have been developed in the used in-house solver SFELES, including the implementation of a new SGS model, a new outlet boundary condition and a new transient format which is used to extract the noise sources to be exported to the acoustic solver, ACTRAN. The second part of this thesis is concerned with the aeroacoustic study where four methods have been applied, among them two are integral formulations and the two others are partial-differential equations. The first method applied is Amiet’s theory, implemented in Matlab, based on the wall-pressure spectrum extracted in a point near the trailing edge. The second method is Curle’s formulation. It is applied proposing two approaches; the first approach is the implementation of the volume and surface integrals in SFELES to be calculated simultaneously with the flow in order to avoid the storage of noise sources which requires a huge space. In the second approach, the fluctuating aerodynamic forces, already obtained during the aerodynamics simulation, are used to compute the noise considering just the surface sources. Finally, Lighthil and Möhring analogies have been applied via the acoustic solver ACTRAN using sources extracted via SFELES. Maps of the radiated noise are demonstrated for several frequencies. The refraction effects of the mean flow have been studied.<br>Doctorat en Sciences de l'ingénieur et technologie<br>info:eu-repo/semantics/nonPublished
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Frank, Hannes [Verfasser]. "High Order Large Eddy Simulation for the Analysis of Tonal Noise Generation via Aeroacoustic Feedback Effects at a Side Mirror / Hannes Frank." München : Verlag Dr. Hut, 2017. http://d-nb.info/1147674434/34.
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Dizemen, Ilke Evrim. "Assessment Of An Iterative Approach For Solution Of Frequency Domain Linearized Euler Equations For Noise Propagation Through Turbofan Jet Flows." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609095/index.pdf.
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This study, explores the use of an iterative solution approach for the linearized Euler equations
formulated in the frequency domain for fan tone noise propagation and radiation through bypass
jets. The aim is to be able to simulate high frequency propagation and radiation phenomena
with this code, without excessive computational resources. All computations are performed
in parallel using MPI library routines on a computer cluster. The linearized Euler equations
support the Kelvin-Helmholtz type convective physical instabilities in jet shear flows. If these
equations are solved directly in frequency domain, the unstable modes may be filtered out for
the frequencies of interest. However, direct solutions are memory intensive and the reachable
frequency is limited. Results provided shown that iterative solution of LEE is more efficient
when considered memory requirement and might solve a wider scope of frequencies, if the
instabilities are controlled.
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Frank, Hannes [Verfasser], and Claus-Dieter [Akademischer Betreuer] Munz. "High order large eddy simulation for the analysis of tonal noise generation via aeroacoustic feedback effects at a side mirror / Hannes Frank ; Betreuer: Claus-Dieter Munz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1147381550/34.
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Caldas, Luciano Coutinho. "In-duct beamforming and mode detection using a circular microphone array for the characterisation of broadband aeroengine fan noise." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-29082016-142207/.
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The development of technologies to reduce turbofan engine noise reveals the fan noise, the first stage of an engine, as a great contributor for the total noise of an airplane. So a better understanding of the fan noise generation came up and motivated the construction of a fan rig test facility at the University of São Paulo in São Carlos by a partnership between the university and EMBRAER S.A.. The fan rig is composed of a long duct (12mlong) comprising a 16-bladed fan rotor and 14-vaned stator. The rotor is powered by an 100 hp electrical motor allowing speed up to 4250 RPM resulting in 0.1Mach axial flow. A 77-microphone wall-mounted array was designed for fan noise analysis. A cooperation with NASA-Glenn allowed data and information exchanging from their similar fan rig setup, the ANCF, grating then the validation of the in-house developed software. A short guide for duct-array is proposed in this work. Complex software was developed to process the data from the microphones array. We performed 3 different types of analysis: power spectral density, noise imaging obtained by acoustic beamforming and modal analysis.We proposed a different technique for modal analysis based on beamforming images in this work.We did not find any similar technique in the references. The results obtained by this technique were validated with data from ANCF-NASA. Comparative results are presented for both fan rigs, such as: power spectral densities for different fan speeds, modal analysis at the blade passing frequency (strong tones generated by the fan), noise imaging obtained by beamforming for rotating and static noise sources. Finally, results achieved in this work are in agreement with those observed in the references consulted.<br>Como desenvolver de tecnologias para redução de ruído de motores aeronáuticos turbofans, o ruído gerado pelo fan (primeiro estágio do motor) vem se mostrando cada vez mais um grande contribuinte na emissão total de ruído em um avião. Com isso, a necessidade de se estudar mecanismos geradores de ruído nestes motores veio à tona e motivou a construção de uma bancada de experimentos aero-acústicos junto àUniversidade de São Paulo, campus São Carlos, oriundo da parceria entre EMBRAER S.A. e Universidade de São Paulo. A bancada de ensaios compõe um conjunto rotor/estator, sendo que o fan (rotor) é equipado com 16 pás e a estatora 14 pás, conectado a um motor elétrico de 100 hp através de um eixo ao rotor, alcançando 4250 RPM com velocidade de escoamento axial médio de 0,1 Mach. Esta bancada é composta por um longo duto e a seção de ensaio com o fan localiza-se ao centro. Uma antena dispondo de 77 microfones foi especialmente projetada para fazer aquisição do ruído gerado pelo fan. Uma parceria com a NASA-Glenn possibilitou a troca de informações e dados experimentais de sua bancada de experimentos similar (ANCF) ajudando assim a validar os códigos desenvolvidos bem como comparar resultados para ambas as bancadas. Umpequeno roteiro para projeto de antena para análise modal e beamforming em duto é apresentado neste trabalho. Um complexo software foi desenvolvido a fim de processar sistematicamente os dados aquisitados pelos microfones da antena. Três tipos de análise são feitas: Via espectro densidade de potência; Imagem de ruído acústico obtido através da técnica de beamforming, e por último, análise modal. Uma técnica diferente para análise modal baseada em imagens obtidas através de beamforming é proposta neste trabalho. Nada similar foi encontrado nas referências consultadas. Os resultados foram validados com dados de fontes sintéticas produzidas pela bancada ANCF-NASA. Resultados comparativos para ambas as bancadas são exibidas neste trabalho, tais quais: Análise do espectro densidade de potência para diferentes rotações do fan; análise modal nas frequências de passagem das pás (forte ruído tonal gerado pelo fan); imagem acústica do ruído gerado tanto por fontes rotativas quanto para fontes estáticas. Finalmente, os resultados obtidos estão de acordo com o esperado e de antemão observados nas referências consultadas.
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Ansaldi, Tobias. "Compressible single and dual stream jet stability and adjoint-based sensitivity analysis in relationship with aeroacoustics." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17505/13/Ansaldi_Tobias.pdf.
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This thesis leads to a better knowledge of the physic and of the control of acoustic radiation in turbulent single and dual-stream jets.It is known that jet noise is produced by the turbulence present in the jet that can be separated in large coherent structures and fine structures. It is also concluded that these large-scale coherent structures are the instability waves of the jet and can be modelled as the flow field generated by the evolution of instability waves in a given turbulent jet. The growth rate and the streamwise wavenumber of a disturbance with a fixed frequency and azimuthal wavenumber are obtained by solving the non-local approach called Parabolized Stability Equations (PSE). Typically the Kelvin-Helmholtz instability owes its origin into the shear layer of the flow and, moreover, the inflection points of the mean velocity profile has a crucial importance in the instability of such a flow. The problem is more complex in case of imperfectly expanded jet where shock-cells manifest inside the jet and strongly interaction with the instability waves has been observed. Several configurations are tested in this thesis, from a subsonic incompressible case to the dual-stream underexpanded supersonic jet obtained by solving Large Eddy Simulations LES (CERFACS). The acoustic far-field is determined by the Ffowcs-Williams-Hawkings acoustic analogy. Then a sensitivity analysis of the jet with respect to external forcing acting in a localized region of the flow are investigated by solving the adjoint PSE equations. High sensitivity appeared in the shear-layer of the flow showing, also, a high dependency in the streamwise and radial direction. In the case of dual-stream jet the propagation of the instability in the inner and outer shear layer should be taken into account. This configuration leads to two different distinct Klevin-Helmholtz modes that are computed separately. The highest sensitivity is determined in the exit of the nozzle outside of the potential core of the jet. In addition, comparison between sensitivity computed by adjoint equations and Uncertainty Quantification (UQ) methods has been done, in the case of a single-stream jet, showing a link between these two methods for small variations of the input parameters. This result leads to the application of a lower cost tool for mathematical analysis of complex problem of industrial interest. This work and in particular the sensitivity theory investigated in this thesis contribute to a development of a new noise control strategy for aircraft jet.
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Van, Herpe Francois. "Computational aeroacoustics for turbulent duct flow." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336488.
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梁志堅 and Chi-kin Randolph Leung. "Studies in aeroacoustics of coaxial vortex rings." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B30166068.
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Leung, Chi-kin Randolph. "Studies in aeroacoustics of coaxial vortex rings /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19003158.
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Júnior, Carlos do Carmo Pagani. "Mapeamento de fontes aeroacústicas de um eslate em túnel de vento de seção fechada utilizando beam-forming com deconvolução DAMAS." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-06122014-232641/.
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A redução do ruído externo gerado por aeronaves operando nas proximidades de grandes centros urbanos é apontada como uma questão vital para a manutenção e expansão sustentável das atividades da aviação civil. Nas últimas décadas, reduções significativas no ruído gerado pelos sistemas de propulsão da aeronave tornaram relevantes as contribuições do trem de pouso e dos dispositivos de hiper-sustentação (flapes e eslates) para o ruído global da aeronave. A caracterização do espectro acústico de cada componente hiper-sustentador é necessária para o desenvolvimento de métodos preditivos de ruído e projetos aerodinâmicos que viabilizem a redução de ruído sem penalizações severas para o desempenho e a segurança da aeronave. Experimentos com modelos em escalas mostram que a contribuição de cada elemento hiper-sustentador para o ruído global é determinada pelo tamanho e modelo da aeronave. Tal fato dificulta a generalização dos resultados experimentais e determina a caracterização do espectro acústico de cada componente de um aerofólio em termos de sua geometria e configuração operacional. Este trabalho tem como objetivo principal a caracterização do ruído do eslate a partir de medições experimentais com um aerofólio hiper-sustentador McDonnell Douglas (30P30N), composto por flape, eslate e elemento principal. Os experimentos foram realizados em túnel de vento de seção fechada, e as medições acústicas contaram com o uso de uma antena composta por 62 microfones. Os dados acústicos foram processados com algoritmos de beam-forming convencional e deconvolução DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources). A aplicação de técnicas de beam-forming permite representar uma distribuição espacial de fontes na forma de um mapa acústico e determinar o nível de ruído gerado por fontes que concorrem de forma independente para o ruído global. A base de dados experimentais permite o estudo do ruído do eslate sob diferentes configurações operacionais e geométricas do aerofólio. A análise do espectro acústico do eslate revela a ocorrência de ruído tonal em baixa e alta frequências, e ruído de banda larga em média frequência. Os mapas de beam-forming obtidos associam o ruído de banda larga com uma distribuição bidimensional de fontes ao longo da envergadura do eslate. O ruído do eslate aumenta com a velocidade de escoamento livre, enquanto que os picos tonais de baixa frequência e o ruído de banda larga decrescem com o aumento do ângulo de ataque do aerofólio de 2° para 10°. Os espectros de ruído do eslate colapsam quando reescalados pelo número de Mach do escoamento livre elevado a uma potência entre 4 e 5, e o ruído tonal colapsa em Strouhal dado pela corda do eslate e pela velocidade do escoamento base. Os resultados mostram que o ruído do eslate é fortemente dependente da geometria do aerofólio, particularmente para variações de overlap. Uma boa correspondência quantitativa foi obtida comparando-se espectros experimentais de ruído do eslate com espectros numéricos, obtidos a partir de um modelo com a mesma geometria e em condições de teste idênticas, o que indica a viabilidade do uso de túneis de vento de secção fechada para a realização de experimentos aeroacústicos.<br>The reduction in the noise produced by aircraft operating in the vicinity of large urban centers is an important issue for a sustainable growth in the civil aviation activities. Over the last decades, from a signicant reduction achieved in the noise generated by aircraft propulsion systems, the contribution of both landing gears and high-lift devices (flaps and slats) has become important to the aircraft overall noise. The identication of the noise signature of each high-lift component is required for the development of both noise prediction methods and new aerodynamic design concepts toward achieving a noise reduction without severe penalty over the aircraft performance and safety. Scaled model experiments have shown that the importance of each airframe component to the overall noise is determined by particularities in both aircraft geometry and size. Such noise model dependence hampers the generalization of experimental results from a reference testing model and leads to the necessity of assessing noise generation according to the testing model geometry and operational condition. This study focuses mainly on the characterization of slat noise from experimental measurements on a high-lift Mcdonnell Douglas (30P30N) airfoil, composed of a slat, a ap and a main element. Measurements were performed in a closed-section wind tunnel by a 62-microphone array and the acoustic data were processed with in-house codes based on conventional beam-forming and DAMAS (Deconvolution Approach for theMapping of Acoustic Sources) algorithms. Beam-forming techniques potentially enable the representation of a spatial source distribution as an acoustic map, from which the contribution of independent sources to the overall noise can be estimated. The experimental database enables the study of the slat noise from dierent airfoil operational conditions and geometrical settings. The slat noise spectral signature reveals the occurrence of tonal noise over both low- and high-frequency bands and also broadband noise over a mid-frequency range. Beam-forming maps indicate the slat broad-band noise originates from a source spatially distributed along the slat span. The slat noise increases in function of the ow speed, whereas low-frequency tonal peaks and the broadband noise decrease as the airfoil angle of attack increases from 2 to 10. The slat noise spectra scalle when the Mach number is raised to a power between 4 and 5, and the tonal noise collapses with Strouhal based on the slat chord and the ow speed. Results show the slat noise is strongly in uenced by the airfoil geometry, particularly for variations in the overlap. A good quantitative agreement was achieved through the comparison between the experimental and numerical slat noise spectra for the same model geometry and test conditions, which indicates the viability of performing aeroacoustic experiments in closed-section wind tunnels.
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鄧兆強 and Shiu-keung Tang. "The aeroacoustics of free shear layers and vortex interactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31233235.
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Peake, Nigel. "The aeroacoustics of high-speed propellers and fans." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387124.
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Pande, Abhijit. "Effect of struts on aeroacoustics of axisymmetric supersonic inlets." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07292009-090449/.
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Cand, Matthew Morgan. "A 3D high-order aeroacoustics model for turbomachinery fan noise propagation." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424998.
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Ewert, Roland [Verfasser]. "A Hybrid Computational Aeroacoustics Method to Simulate Airframe Noise / Roland Ewert." Aachen : Shaker, 2003. http://d-nb.info/1179034333/34.
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Ahmad, Arsalan. "Experimental aeroacoustics study on jet noise reduction using tangential air injection." Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2319.
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Aircraft jet exhausts are a source of undesirable noise and continue to be an area of investigation driven by increasingly stringent regulation. The noise is produced by the unsteady mixing of the jet with the surrounding air and is dominated by the effects of the shear layer. In this study, the mechanisms of noise suppression are investigated on an unheated Mach 1.3 jet through three distinct control techniques. The first consists of tangential steady flow injectors located upstream of the nozzle exit whereas the second involves an equal number of control jets spaced further downstream around the nozzle exit. The third technique pulses air tangential into the shear layer at a frequency coinciding with the preferred modes of the jet (St~0.17, f~2kHz). Near and far-field acoustic measurements were made in anechoic chamber with an array of 10 free-field microphones. All three forms of tangential air injection induced reductions in overall sound pressure levels (OASPL) across a range of observer angles. External tangential injection was found to be the most efficient technique, as it produced comparably similar noise reductions at only a fraction of the injection mass flow ratio. The most significant acoustic benefit was an 8dB SPL reduction at the sideline observer angle, subsequently eliminating both screech and broadband shock noise at Strouhal numbers of St~0.74 (f~9.6kHz) and St~1(f~13kHz) respectively. An OASPL reduction of up to 5dB was also recorded at a downstream angle of 15º. However, the low-frequency noise benefits from these control jets came at the expense of increased high frequency noise beyond St>2 (f~26kHz). The flow-fields of the jet were observed using stereoscopic Particle Image Velocimetry (PIV). The introduction of a swirling component of velocity downstream of the nozzle exit was found to have a stabilizing effect on the jet shear layer. Reductions in turbulence intensity and Reynolds stress were recorded towards the end of the potential core by up to 18% and 25% respectively. The ultimate objective of this study was to develop an injection configuration that is effective at reducing jet noise whilst minimising penalties in weight and thrust.
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Perrault-Joncas, Dominique C. "Linear stability of coaxial jets with application to aeroacoustics." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112343.
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Motivated by a practical interest in noise generated by turbofan engine, this thesis studies the stability of parallel coaxial jets with velocity and temperature profiles characteristic of the exhaust region of the engine. Because the bypass stream mixes with both the exhaust and the ambient air, these profiles contain thin layers in which the velocity and temperature may vary rapidly. As a consequence, multiple instability modes are possible. In accordance with Rayleigh's theorem for axisymmetric incompressible shear flows, it follows that there are three possible modes, only two of which are unstable. To complement the study of parallel flow stability, this thesis also includes the derivation of the amplitude evolution equation for slowly varying axisymmetric incompressible flows.
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Tang, Shiu-keung. "The aeroacoustics of free shear layers and vortex interactions /." [Hong Kong] : University of Hong Kong, 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13311633.
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Saunders, Christopher A. II. "Noise Reduction in an Axisymmetric Supersonic Aircraft Inlet using Trailing Edge Blowing." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/31385.
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Acoustic experiments were conducted in an anechoic chamber with a 1/14th scale model of a supersonic aircraft engine inlet using Trailing Edge Blowing (TEB) to reduce the engine fan noise from a turbofan propulsion simulator (TPS). The TPS is 4.1 in. (10.4 cm) in diameter and is powered by compressed air. The supersonic inlet is connected to the TPS and is geometrically and acoustically scaled from a working design. The supersonic inlet is operated in a takeoff or landing operating condition where the inlet core flow is subsonic. TEB is the process of ejecting high pressure air to re-energize the wakes of upstream fan disturbances such as struts or inlet guide vanes (IGV). The elimination of the wakes will provide a uniform flow field at the engine fan face and reduce noise at the blade passing frequency. The TEB was implemented on six non-uniformly spaced support struts in the inlet. Acoustic tests were then performed at 40%, 60% and 88% of the fan design speed (PNC) to measure the reduction in the blade passing tone (BPT) due to TEB from the struts with and without the presence of IGV.
The noise reductions without IGV at 40 PNC show the best results with the blade passing tone (BPT) being reduced by an average of 3.1 dB. The first harmonic of the BPT and the overall Sound Pressure Level (SPL) were also reduced by 1 dB. The addition of the IGV in the inlet reduced the effectiveness of the TEB. The addition of IGV changed the reduction in BPT at 40 PNC by 0.5 dB and the overall SPL was unchanged. At 60 PNC the addition of IGV reduced the reduction due to TEB in the BPT from an average of 2 dB to an average of 1 dB. The tests performed at 88 PNC showed negligible effects due to TEB. Aerodynamic experiments performed on the inlet that showed that the wakes of the IGV have a larger velocity defect than the struts, thus making the IGV a greater noise source.<br>Master of Science
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Thomas, Paul Huw. "High fidelity open rotor noise prediction." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270307.
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As improving the performance of turbofan designs becomes increasingly difficult, manufacturers are looking to new technologies for the next generation of jet engines. An 'open rotor' replaces the fan of the turbofan with a set of external rotors. This has the potential to offer a significant improvement in propulsive efficiency, but the design for low noise is a key challenge. Hence, high fidelity noise prediction methods are needed to accurately predict and compare the noise of different designs. This thesis focuses on one set of methods based on the Ffowcs Williams-Hawkings (\fwh) equation. This equation is considered to be the most realistic description of aeroacoustic noise generation, as it is a direct rearrangement of the Navier-Stokes equations. The \fwh\ equation is difficult to solve for realistic test cases such as an open rotor, and is susceptible to several types of error. This thesis categorises these errors as ``input'', ``neglection'' and ``discretisation'' errors. Discretisation errors arise from the need to integrate a discretised source field for the total noise, neglection errors result from needing to ignore part of the source field for practical reasons, and input errors relate to any errors caused by inaccurate input to the solver. The fundamental motivation of this thesis is to advance the understanding of neglection and discretisation errors and how they can be mitigated, in order to develop best practice solvers and methodologies for application to open rotors. Dimensional analysis is combined with analytical flow solutions to develop a process for isolating and quantifying discretisation errors. This process is used to study a wide range of solver methodologies and select a best practice solver methodology for open rotor noise prediction. This first-of-a-kind study produces a solver methodology that reduces discretisation errors by an order of magnitude compared to an industry standard solver. Previous research into neglection errors has shown that avoiding density perturbations in acoustic source terms can be beneficial. This thesis uses a generic aeroacoustic analogy to provide a new, physically intuitive method of incorporating a surface discontinuity that enables density perturbations to be avoided in a far more elegant manner than previous research. The above method improvements are investigated using a modern open rotor rig test case. The results demonstrate that discretisation and neglection errors can be severe in realistic cases and the potential of the method improvements to significantly mitigate them.
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Parsons, C. "An experimental and theoretical study of the aeroacoustics of external-Coanda gas flares." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384704.
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Lim, Teck-Bin. "A unified computational fluid dynamics-aeroacoustics analysis of high speed propeller." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/12064.
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Daniel, Kyle Andreas. "Space-time Description of Supersonic Jets with Thermal Non-uniformity." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/95942.
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The supersonic jet plumes that exhaust from the engines of tactical aircraft produce intense noise signatures that expose the Navy personnel working on the deck of aircraft carriers to dangerously high levels of noise that often results in hearing damage. Reducing the noise radiated by these supersonic plumes is of interest to the Department of Defense and is the primary motivation of this research. Fundamentally, jet noise reduction is achieved by manipulating the nozzle boundary condition to produce changes in the turbulence development and decrease the acoustic efficiency of coherent structures. The research presented here focuses on a novel jet noise reduction technique involving a centered thermal non-uniformity that alters the base flow by introducing a temperature-driven centerline velocity deficit into a perfectly expanded Mach 1.5 jet. The results indicate $2 pm 0.5$ dB reductions in peak narrowband spectral sound pressure levels upstream of peak directivity directions for the non-uniform jet compared to a thermally uniform baseline, even for static thrust matched conditions. This reduction is hypothesized to be related to perturbations induced by the thermal non-uniformity that convect inside the irrotational core and reduce the correlation length scales of turbulence at locations far downstream. This hypothesis was evaluated by studying the coherent turbulence via its convective hydrodynamic footprint in the near-field. An indirect investigation of the near-field using a far-field-informed model of the wavenumber-frequency spectra indicate a reduction in the energy contained in the tail of the wavenumber spectra amplitude, suggesting a reduction in the size of large scale structures. A direct evaluation of the spatio-temporal behavior of the near-field was performed using temporally resolved schlieren images. Space-time correlations of the frequency-filtered near-field identified high frequency acoustic waves radiated by compactly coherent turbulent structures and low frequency Mach waves produced by large scale instabilities. In the thermally non-uniform case these features and their sources were found to be decorrelated at downstream regions. These results provide strong evidence that a centered thermal non-uniformity reduces the radiated noise compared to a uniform baseline by shortening the correlation length scales of coherent structures in regions far from the nozzle exhaust.<br>Doctor of Philosophy<br>A more complete understanding of the intense noise sources present in supersonic jet plumes is of value to both government and industry, and is a necessary step towards optimizing noise reduction techniques. Tactical aircraft that operate on the deck of aircraft carriers expose Navy personnel to dangerously high levels of noise that often results in permanent hearing damage. Supersonic jet noise reduction is also of relevance to the recent efforts to revitalize supersonic air transport over land. For supersonic air transport to become a reality, the noise produced by these future aircraft during takeoff and landing must meet the increasingly stringent community noise requirements. Fundamental jet noise research is needed to guide the design of future engine architectures for these aircraft to ensure their commercial success. The research presented herein examines a novel noise reduction technique that involves a centered thermal non-uniformity consisting of a heated jet plume with a spot of locally cooler, slower moving air concentrated along the centerline of a Mach 1.5 jet. This temperature driven velocity deficit is shown to reduce the radiated noise by up to 2.5 dB at peak frequencies and at angles just outside of the peak directivity direction. The cause of the noise reduction is hypothesized be related to a reduction in the size of the coherent structures that radiate a majority of the noise produced by turbulent jets. This hypothesis is evaluated by examining the 'footprint' of the coherent structures in the ambient field directly outside of the jet shear layer in an area called the near-field. An indirect investigation of the near-field using a far-field informed analytic model suggests a reduction in the size of large scale structures. A direct evaluation of the space time structure of the near-field was performed using temporally resolved schlieren images. Statistical processing of the density gradient provided by the schlieren images revealed acoustically intense structures known as Mach waves and high frequency acoustic waves. These features and their sources, large scale instabilities and compactly coherent turbulence, were found to be decorrelated by the introduction of the thermal non-uniformity. These results provide strong evidence that the centered thermal non-uniformity produces a noise benefit by reducing the size of the turbulent structures.
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Clark, Ian Andrew. "Bio-Inspired Control of Roughness and Trailing Edge Noise." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77531.
Full textAbstract:
Noise from fluid flow over rough surfaces is an important consideration in the design and performance of certain vehicles with high surface-area-to-perimeter ratios. A new method of noise control based on the anatomy of owls is developed and consists of fabric or fibrous canopies suspended above the surface. The method is tested experimentally and is found to reduce the total far-field noise emitted by the surface. The treatment also is found to reduce the magnitude of pressure fluctuations felt by the underlying surface by up to three orders of magnitude. Experimental investigations into the effects of geometric parameters of the canopies lead to an optimized design which maximizes noise reduction.
The results obtained during the canopy experiment inspired a separate new device for the reduction of trailing edge noise. This type of noise is generated by flow past the wing of an aircraft or the blades of a wind turbine, and is a source of annoyance for those in surrounding communities. The newly developed treatment consists of small fins, or "finlets," placed near the trailing edge of an airfoil. The treatment is tested experimentally at near-full-scale conditions and is found to reduce the magnitude of far-field noise by up to 10 dB. Geometric parameters of the finlets are tested to determine the optimal size and spacing of the finlets to maximize noise reduction. Follow-up computational and experimental studies reveal the fluid mechanics behind the noise reduction by showing that the finlets produce a velocity deficit in the flow near the trailing edge and limit the magnitude and spanwise correlation lengthscale of turbulence near the trailing edge, factors which determine the magnitude of far-field noise.
In a final experiment, the finlets are applied to a marine propeller and are found to reduce not only trailing edge noise, but also noise caused by the bluntness of the trailing edge. The results of this experiment show the potential usefulness of finlets to reduce noise from rotating systems, such as fans or propellers, as well as from structures which feature blunt trailing edges.<br>Ph. D.
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Robison, Rosalyn Aruna Venner. "Turbulence ingestion noise of open rotors." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243244.
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Renewed interest in open rotor aeroengines, due to their fuel efficiency, has driven renewed interest in all aspects of the noise they generate. Noise due to the ingestion of distorted atmospheric turbulence, known as Unsteady Distortion Noise (UDN), is likely to be higher for open rotors than for conventional turbofan engines since the rotors are fully exposed to oncoming turbulence and lack ducting to attenuate the radiated sound. However, UDN has received less attention to date, particularly in wind-tunnel and flight testing programmes. In this thesis a new prediction scheme for UDN is described, which allows inclusion of many key features of real open rotors which have not previously been investigated theoretically. Detailed features of the mean flow induced by the rotor, the form of atmospheric turbulence, asymmetries due to installation features, and the effect of rotor incidence are all considered. Parameter studies are conducted in each of these cases to investigate their effect upon UDN in typical static testing and flight conditions. A thorough review of the technological issues of most relevance and previous theoretical work on all types of turbulence-blade interaction noise is first undertaken. The prediction scheme is then developed for the case in which the mean flow into the rotor is axisymmetric. This shows excellent qualitative agreement with previous findings, with increased streamtube contraction resulting in a more tonal noise spectrum. The theoretical framework involves using Rapid Distortion Theory to calculate the distortion of an isotropic turbulence field (such as given by the von Karman spectrum) by the mean flow induced by the rotor (such as given by actuator disk theory), leading to an expression for the velocity incident upon the leading edge of the rotor blades. Strip theory is then used to calculate the pressure jumps across the blades, input as the forcing term in the far-field wave equation. Models are derived for open rotor-induced flow which account for the variation of blade circulation with radius, and the presence of the rotor hub and rear blade row. An investigation of appropriate turbulence models and realistic turbulence parameters is also undertaken. A key finding is that the heights of the tonal peaks are determined by the overall magnitude of the induced streamtube contraction (dependent on the total thrust generated) whereas the precise form of distortion (affected by the detailed components of the mean flow and the form of atmospheric turbulence present) alters the resulting broadband level. The prediction scheme is formulated in such a way as to facilitate extension to the asymmetric case, which is also fully derived. The model is applied in the first instance to the case of two adjacent rotors and then to the case of a single rotor at incidence. Under flight conditions, when distortion is reduced but UDN can still contribute a significant broadband component to overall noise levels, asymmetry is found to increase broadband levels around 1 Blade Passing Frequency but reduce levels elsewhere.
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Gonzalez, David R. "Development of a Semi-Lagrangian Methodology for Jet Aeroacoustics Analysis." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1467201142.
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MYERS, MATTHEW RONALD. "EFFECT OF AIRFOIL MEAN LOADING ON HIGH-FREQUENCY GUST INTERACTION NOISE (AEROACOUSTICS, FAN, TURBOMACHINERY)." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184032.
Full textAbstract:
This dissertation investigates the effect of airfoil steady loading on the sound generated by the interaction of an isolated, zero-thickness airfoil with a high-frequency convected disturbance. The analysis is based on a linearization of the inviscid equations of motion about a nonuniform mean flow. The mean flow is assumed to be two-dimensional and subsonic. Throughout most of the dissertation, we assume that the Mach number is 0(1), though in one section we concentrate on the leading-edge region and study the behavior of the sound field as the Mach number tends to zero. The small parameter representing the amount of airfoil camber and incidence angle, and the large parameter representing the ratio of airfoil chord to disturbance wavelength, are utilized in a singular perturbation analysis. The analysis shows that essentially all of the sound is generated at the leading and trailing edges, in regions the size of the disturbance wavelength. The solution in the local-leading-edge region reveals several sound-generating mechanisms which do not exist for an airfoil with no mean loading. These mechanisms are not present at the trailing edge; the trailing edge is important only as a scatterer of the sound produced at the leading edge. The propagation of sound away from the airfoil edges is described by geometric acoustics, with the amplitude varying on the scale of the airfoil chord and the phase varying on the much smaller scale of the disturbance wavelength. In addition, a diffraction-type transition region exists downstream of the airfoil. Calculations of radiated acoustic power show that the sound field depends strongly on Mach number, gust characteristics, and airfoil steady loading. Small changes in these properties can produce large changes in radiated power levels. Most importantly, we find that the amount of power radiated correlates very well with the strength of the mean flow around the leading edge.