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Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, 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: urn:nbn:se:kth:diva-33763ISBN: 978-91-7501-008-3OAI: oai:DiVA.org:kth-33763DiVA: diva2:417318
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
List of papers
1. A frequency domain linearized Navier-Stokes equations approach to acoustic propagation in flow ducts with sharp edges
Open this publication in new window or tab >>A frequency domain linearized Navier-Stokes equations approach to acoustic propagation in flow ducts with sharp edges
2010 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 127, no 2, 710-719 p.Article in journal (Refereed) Published
Abstract [en]

Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.

Keyword
acoustic wave propagation, aeroacoustics, Navier-Stokes equations, orifices (mechanical), pipe flow, finite-element method, low-mach-number, sound-absorption, 4-pole, parameters, bias flow, orifice, expansions, scattering, matrix, slit
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-19184 (URN)10.1121/1.3273899 (DOI)000274322200022 ()2-s2.0-76349094069 (ScopusID)
Note

QC 20150727

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2015-07-27Bibliographically approved
2. Simulations of the scattering of sound waves at a sudden area expansion
Open this publication in new window or tab >>Simulations of the scattering of sound waves at a sudden area expansion
2012 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 5, 1068-1083 p.Article in journal (Refereed) Published
Abstract [en]

The scattering of acoustic plane waves at a sudden area expansion in a flow duct is simulated using the linearized Navier-Stokes equations. The aim is to validate the numerical methodology for the flow duct area expansion, and to investigate the influence of the downstream mean flow on the acoustic scattering properties. A comparison of results from numerical simulations, analytical theory and experiments is presented. It is shown that the results for the acoustic scattering obtained by the different methods gives excellent agreement. For the end correction, the numerical approach is found superior to the analytical model at frequencies where coupling of acoustic and hydrodynamic waves is significant. A study with two additional flow profiles, representing a non-expanding jet with infinitely thin shear layer, and an immediate expansion, shows that a realistic jet is needed to accurately capture the acoustic-hydrodynamic interaction. A study with several different artificial jet expansions concluded that the acoustic scattering is not significantly dependent on the mean flow profile below the area expansion. The constructed flow profiles give reasonable results although the reflection and transmission coefficients are underestimated, and this deviation seems to be rather independent of frequency for the parameter regime studied. The prediction of the end correction for the constructed mean flow profiles deviates significantly from that for the realistic profile in a Strouhal number regime representing strong coupling between acousticand hydrodynamic waves. It is concluded that the constructed flow profiles lack the ability to predict the loss of energy to hydrodynamic waves, and that this effect increases with increasing Mach number.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
aeroacoustics, frequency-domain, linearized Navier-Stokes, scattering, duct
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-33774 (URN)10.1016/j.jsv.2011.09.011 (DOI)000299459100008 ()2-s2.0-82955247818 (ScopusID)
Funder
TrenOp, Transport Research Environment with Novel PerspectivesSwedish e‐Science Research Center
Note

QC 20120309

Available from: 2011-05-17 Created: 2011-05-17 Last updated: 2013-04-08Bibliographically approved
3. Simulations of whistling and the whistling potentiality of an in-duct orifice with linear aeroacoustics
Open this publication in new window or tab >>Simulations of whistling and the whistling potentiality of an in-duct orifice with linear aeroacoustics
2012 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 5, 1084-1096 p.Article in journal (Refereed) Published
Abstract [en]

This paper demonstrates a linear aeroacoustic simulation methodology to predict the whistling of an orifice plate in a flow duct. The methodology is based on a linearized Navier-Stokes solver in the frequency domain with the mean flow field taken from a Reynolds-Averaged Navier-Stokes (RANS) solution. The whistling potentiality is investigated via an acoustic energy balance for the in-duct element and good agreement with experimental data is shown. A Nyquist stability criterion based on the simulation data was applied to predict whistling of the orifice when placed in a finite sized duct and experiments were carried out to validate the predictions. The results indicate that although whistling is a non-linear phenomena caused by an acoustic-flow instability feed-back loop, the linearized Navier-Stokes equations can be used to predict both whistling potentiality and a duct system’s ability to whistle or not.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
aeroacoustics, frequency-domain, linearized Navier-Stokes, scattering, duct
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-33779 (URN)10.1016/j.jsv.2011.10.028 (DOI)000299459100009 ()2-s2.0-82955233114 (ScopusID)
Funder
TrenOp, Transport Research Environment with Novel PerspectivesSwedish e‐Science Research Center
Note

QC 20120309

Available from: 2011-05-17 Created: 2011-05-17 Last updated: 2013-04-22Bibliographically approved
4. Flow field eigenmode decompositions in aeroacoustics
Open this publication in new window or tab >>Flow field eigenmode decompositions in aeroacoustics
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.

Keyword
boundary-layer-flow, oscillations, models
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-19014 (URN)10.1016/j.compfluid.2009.09.010 (DOI)000272404900014 ()2-s2.0-70350732792 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-05-17Bibliographically approved

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