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Sound propagation from sustainable ground vehicles: from aeroacoustic sources to urban noise
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.ORCID iD: 0000-0002-7006-067X
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xiii, 65 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:67
Keyword [en]
sound propagation, sound generation, ground vehicle, aeroacoustics, aerodynamics, Kirchhoff approximation, detached eddy simulation, Ffowcs Williams and Hawkings
Keyword [sv]
ljudutberdning, ljudalstring, markfordon, aeroakustik, aerodynamik, Kirchhoff approximation, detached eddy simulation, Ffowcs Williams and Hawkings
National Category
Fluid Mechanics and Acoustics Vehicle Engineering
Research subject
Vehicle and Maritime Engineering; Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-174182ISBN: 978-91-7595-704-3 (print)OAI: oai:DiVA.org:kth-174182DiVA: diva2:858252
Presentation
2015-10-15, D2, Lindstedtsvägen 5, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20151002

Available from: 2015-10-02 Created: 2015-10-01 Last updated: 2015-10-02Bibliographically approved
List of papers
1. The impact of traffic noise on economy and environment: a short literature study: Performed within the scope of the ECO2 project Noise propagation from sustainable ground vehicles
Open this publication in new window or tab >>The impact of traffic noise on economy and environment: a short literature study: Performed within the scope of the ECO2 project Noise propagation from sustainable ground vehicles
2015 (English)Report (Other academic)
Abstract [en]

This report discusses the societal impacts of environmental and traffic noise, and the benefits that could be withdrawn from their reduction. Environmental noise pollution is considered as one of the main environmental problems in today’s society. Around 80 million European citizens are exposed to unhealthy noise level. These levels can affect health and well-being, which will be reflected on working and living conditions, consequently affecting the economy. To deal with this issue, always stricter regulations are being voted by states to set up action plans to prevent noise exposure and to reduce the noise at its source. The main source of environmental noise is transportation noise which is pulled up by always increasing needs for goods, energy, and personal transportation. Excluding airways traffic noise which affects only a small percentage of the population, reducing traffic noise comes down to either isolating roads or railways from living and working areas or achieving reductions of noise at its source - on ground vehicles. The position of the ECO2 project Noise propagation from sustainable vehicle concepts in a more global effort to reduce noise pollution is described. The impact of traffic noise on health and environment is discussed, as well as various aspects of the impact on the economy. Estimations of the costs of traffic noise are presented for different types of vehicles, as well as the influence on housing prices. Response from the state in terms of legislation is tackled . Finally, societal benefits of traffic noise reduction are discussed.

Publisher
16 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:29
Keyword
traffic noise, impact, economy, health, vehicle, transportation, noise pollution
National Category
Vehicle Engineering Environmental Engineering Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-166289 (URN)978-91-7595-615-2 (ISBN)
Note

QC 20150518

Available from: 2015-05-15 Created: 2015-05-07 Last updated: 2015-10-02Bibliographically approved
2. Aerodynamic and aeroacoustic analyses of a submerged air inlet in a low-Mach-number flow
Open this publication in new window or tab >>Aerodynamic and aeroacoustic analyses of a submerged air inlet in a low-Mach-number flow
2016 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 133, 15-31 p.Article in journal (Refereed) Published
Abstract [en]

Computational aerodynamic and aeroacoustic analyses of a submerged air inlet are performed at a low Mach number. A hybrid method is used, in which the flow in the vicinity of the inlet is solved through detached eddy simulation (DES) and the acoustic pressure in the far-field is computed through the use of a Ffowcs Williams and Hawkings integral. Several surfaces of integration are used, both solid and permeable. The inlet design is based on an experimental inlet developed by the National Advisory Committee for Aeronautics (NACA). The flow is solved first through steady-state RANS simulation, then time-dependent DES is run from the converged results. The results from both RANS simulations and DES show good agreement with experimental data from NACA, both in terms of integral quantities and surface pressure coefficients. Pressure fluctuations are observed on both sides of the lip of the inlet, and are greater at low velocity ratios, with the velocity ratio defined as the ratio between the flow velocity at the duct entrance and in the free stream. A transition is observed between a quasi-laminar flow at a velocity ratio of 0.8 and a turbulent flow at velocity ratios of 0.6 and 0.4. This turbulent behaviour at low velocity ratios is associated with much higher acoustic levels in the far-field. At low velocity ratios, the acoustic spectra in the far-field exhibit a broadband character with maximum levels distributed around a characteristic frequency given by the ratio between the flow velocity at the duct entrance and the duct entrance depth. At high velocity ratios, the spectra show tonal characteristics with peaks at around 90 percent of this characteristic frequency and at the corresponding harmonics. A comparison between the spectra from solid and permeable surfaces reveals that volume sound sources are negligible at this low Mach number. A visualization of the integrands in the Ffowcs Williams and Hawkings integral show that sound sources are located on both sides of the lip of the inlet, at the position of impact of the vortices, and along the vortex wakes. Some observations regarding the use of solid and permeable surfaces of integration are made.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
submerged air inlet, NACA duct, NACA inlet, detached eddy simulation, DES, Ffowcs Williams and Hawkings
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering; Aerospace Engineering; Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-174180 (URN)10.1016/j.compfluid.2016.04.010 (DOI)000377740000002 ()2-s2.0-84963936303 (Scopus ID)
Note

QC 20160523

Available from: 2015-10-01 Created: 2015-10-01 Last updated: 2017-12-01Bibliographically approved
3. A Kirchhoff approximation-based numerical method to compute multiple acoustic scattering of a moving source
Open this publication in new window or tab >>A Kirchhoff approximation-based numerical method to compute multiple acoustic scattering of a moving source
2015 (English)In: Applied Acoustics, ISSN 0003-682x, Vol. 96, 108-117 p.Article in journal (Refereed) Published
Abstract [en]

Within the scope of a study of external noise propagation from moving ground vehicles, a numerical method is developed to compute the acoustic field emitted by a moving source in the presence of scattering objects such as roads, buildings or noise-shields. This method is developed with the purpose of being used in a vehicle design process and therefore it must have a low computational cost, which requires a certain number of approximations. The case of a fixed point source is studied first then the effect of a movement of the source is taken into account through the introduction of a retarded time. The acoustic source is assumed to be represented by one or many harmonic monopoles of possibly different frequency moving with a constant speed in a quiescent flow field. Scattering from nearby perfectly reflecting objects is computed through a Kirchhoff–Helmholtz integral equation applying the Kirchhoff approximation. A ray-surface intersection algorithm to compute shadow areas is proposed. The method is validated against analytical solutions and experimental results for a fixed source, and against a higher-order finite difference time-domain method for the multiple scattering of a moving source. Results are good and show that this method can potentially be used to predict urban noise.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Multiple scattering, Moving source, Kirchhoff–Helmholtz integral, Kirchhoff approximation, Urban noise
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-163047 (URN)10.1016/j.apacoust.2015.03.016 (DOI)000355033900013 ()2-s2.0-84926306952 (Scopus ID)
Note

QC 20150424

Available from: 2015-03-26 Created: 2015-03-26 Last updated: 2017-12-04Bibliographically approved

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Pignier, Nicolas

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