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Flow field eigenmode decompositions in aeroacoustics
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-9061-4174
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.ORCID iD: 0000-0001-7864-3071
2010 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 39, no 2, 338-344 p.Article in journal (Refereed) Published
Abstract [en]

In this paper an efficient method to study sound generation processes in low Mach number flows is presented. We apply the methodology on a two-dimensional flow over a cavity with smoothed corners. Instead of the full flow field obtained from, for example a Direct Numerical Simulation (DNS), we use a reduced model based on global modes to obtain the aeroacoustic sources. Global modes are eigenmodes to the Navier-Stokes equations, linearized about a steady base flow. In a reduced model the perturbations from a steady state are approximated by a linear combination of the eigenmodes. The time dependence is determined by the corresponding eigenvalues. Curie's equation is used to calculate the acoustic field, and by studying the source terms in Curie's equation, mechanisms for sources of sound are identified. Results of acoustic pressure in the far-field and source strengths for different superpositions of eigenmodes are presented.

Place, publisher, year, edition, pages
2010. Vol. 39, no 2, 338-344 p.
Keyword [en]
boundary-layer-flow, oscillations, models
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-19014DOI: 10.1016/j.compfluid.2009.09.010ISI: 000272404900014Scopus ID: 2-s2.0-70350732792OAI: oai:DiVA.org:kth-19014DiVA: diva2:337061
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Numerical Investigations of Generation and Propagation of Sound Waves in Low Mach Number Internal Flows
Open this publication in new window or tab >>Numerical Investigations of Generation and Propagation of Sound Waves in Low Mach Number Internal Flows
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Traffic is a major source of environmental noise in modern day society. Subsequently, development of new vehicles are subject to heavy governmental legislations. The major noise sources on common road vehicles are engine noise, transmission noise, tire noise and, at high speeds, wind noise. At low speeds (< 30-50 km/h), intake and exhaust noise are particularly important during acceleration. One way to reduce intake and exhaust noise is to attach mufflers to the exhaust pipes. However, to develop prototypes of mufflers for evaluation is a costly and time-consuming process. As a consequence, in recent years so-called virtual prototyping has emerged as an alternative. Current industrial simulation methodologies are often rather simple, either neglecting mean flow or including only one-dimensional mean flows. Also, flow generated noise is rudimentary modeled or not included at all. Hence, improved methods are needed to fully benefit from the possibilities of virtual prototyping.

This thesis is divided in two main parts. The first topic is related to the development and evaluation of methods to simulate sound propagation and generation in two-dimensional confined geometries with arbitrary internal mean flows present. The performance of a new DNS code is evaluated for aeroacoustical purposes and a frequency domain linearized Navier-Stokes equations methodology is developed for acoustic wave propagation applications. Both methods are validated on a case of an in-duct orifice plate.

In the second part, a so-called global mode decomposition technique is evaluated for aeroacoustical purposes. The flow field is described as a sum of the non-orthogonal solutions to its corresponding eigenvalue problem. This enables the acoustic analysis of source terms from each individual global mode, and thus reveals new insight into the sound generating mechanisms.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vi, 33 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:58
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-9388 (URN)
Presentation
2008-10-21, MWL 74, Teknikringen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101115Available from: 2008-10-30 Created: 2008-10-29 Last updated: 2010-11-15Bibliographically approved
2. Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics
Open this publication in new window or tab >>Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Traffic is a major source of environmental noise in modern day's society. As a result, the development of new vehicles are subject to heavy governmental legislations. The major noise sources on common road vehicles are engine noise, transmission noise, tire noise and, at high speeds, wind noise. One way to reduce intake and exhaust noise is to attach mufflers to the exhaust pipes. However, to develop prototypes for the evaluation of muffler performance is a costly and time-consuming process. As a consequence, in recent years so called virtual prototyping has emerged as an alternative. Current industrial simulation methodologies are often rather crude, normally only including one-dimensional mean flows and one-dimensional acoustic fields. Also, flow generated noise is rudimentary modeled or not included at all. Hence, improved methods are needed to fully benefit from the possibilities of virtual prototyping.

This thesis is aimed at the development of simulation methodologies suitable both as industrial tools for the prediction of the acoustic performance of flow duct systems, as well as for analyzing the governing mechanisms of duct aeroacoustics. Special focus has been at investigating the possibilities to use frequency-domain linearized Navier-Stokes equations solvers, where the equations are solved either directly or as eigenvalue formulations.

A frequency-domain linearized Navier-Stokes equations methodology has been developed to simulate sound propagation and acoustic scattering in flow duct systems. The performance of the method has been validated to experimental data and analytical solutions for several cases of in-duct area expansions and orifice plates at different flow speeds. Good agreement has generally been found, suggesting that the proposed methodology is suitable for analyzing internal aeroacoustics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 78 p.
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-33763 (URN)978-91-7501-008-3 (ISBN)
Public defence
2011-05-27, Sal E3, Osquars backe 14, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research CenterTrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20110517Available from: 2011-05-17 Created: 2011-05-16 Last updated: 2012-06-12Bibliographically approved

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Efraimsson, GunillaHenningson, Dan Stefan

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