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The effect of turbulence damping on acoustic wave propagation in tubes
KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO.
KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO.ORCID iD: 0000-0001-7898-8643
2010 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 329, no 22, 4719-4739 p.Article in journal (Refereed) Published
Abstract [en]

The attenuation of sound due to the interaction between a low Mach number turbulent boundary layer and acoustic waves can be significant at low frequencies or in narrow tubes. In a recent publication by the present authors the acoustics of charge air coolers for passenger cars has been identified as an interesting application where turbulence attenuation can be of importance. Favourable low-frequency damping has been observed that could be used for control of the in-duct sound that is created by the engine gas exchange process. Analytical frequency-dependent models for the eddy viscosity that controls the momentum and thermal boundary layers are available but are restricted to thin acoustic boundary layers. For cases with cross-sections of a few millimetres a model based on thin acoustic boundary layers will not be applicable in the frequency range of interest. In the present paper a frequency-dependent axis-symmetric numerical model for interaction between turbulence and acoustic waves is proposed. A finite element scheme is used to formulate the time harmonic linearized convective equations for conservation of mass, momentum and energy into one coupled system of equations. The turbulence is introduced with a linear model for the eddy viscosity that is added to the shear viscosity. The proposed model is validated by comparison with experimental data from the literature.

Place, publisher, year, edition, pages
2010. Vol. 329, no 22, 4719-4739 p.
National Category
Mechanical Engineering Vehicle Engineering
URN: urn:nbn:se:kth:diva-14193DOI: 10.1016/j.jsv.2010.05.018ISI: 000280929700011ScopusID: 2-s2.0-77955418374OAI: diva2:331686
QC 20101130 ändrad från in press till published 20101130Available from: 2010-07-23 Created: 2010-07-23 Last updated: 2011-11-06Bibliographically approved
In thesis
1. Modelling of IC-Engine Intake Noise
Open this publication in new window or tab >>Modelling of IC-Engine Intake Noise
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Shorter product development cycles, densely packed engine compartments and intensified noiselegislation increase the need for accurate predictions of IC-engine air intake noise at earlystages. The urgent focus on the increasing CO2 emissions and the efficiency of IC-engines, aswell as new techniques such as homogeneous charge compression ignition (HCCI) mightworsen the noise situation. Nonlinear one-dimensional (1D) gas dynamics time-domainsimulation software packages are used within the automotive industry to predict intake andexhaust orifice noise. The inherent limitation of 1D plane wave propagation, however, limitsthis technique to sufficiently low frequencies where non-plane wave effects are small. Thereforethis type of method will first fail in large components such as air cleaners. Further limitations,that might not be important for simulation of engine performance but indeed for acoustics,include difficulties to apply frequency dependent boundary conditions and losses as well as toinclude effects of vibrating walls.

The first part of this thesis treats two different strategies to combine nonlinear and linearmodelling of intake systems in order to improve the accuracy of the noise predictions. Paper Adescribes how a linear time-invariant one-port source model can be extracted using nonlineargas dynamics simulations. Predicted source data for a six-cylinder naturally aspirated engine isvalidated using experimental data obtained from engine test bench measurements. Paper Bpresents an experimental investigation on the influence of mean flow and filter paper on theacoustics of air intake systems. It also suggests how a linear source, extracted from nonlinearsimulations can be coupled to acoustic finite elements describing the intake system and toboundary elements describing the radiation to the surroundings. Simulations and measurementsare carried out for a large number of engine revolution speeds in order to make the firstsystematic validation of an entirely virtual intake noise model that includes 3D effects for awide engine speed range. In Paper C an initial study on a new technique for the use of two-portsin the time domain for automotive gas dynamics applications is presented. Tabulated frequencydomaintwo-port data representing an air cleaner unit on the impedance form is inverselytransformed to the time domain and used as FIR filters in nonlinear time-domain calculations.

The second part of the thesis considers detailed modelling of sound propagation in capillarytubes. Thermoviscous boundary effects and interaction between sound waves and turbulencecan, for sufficiently narrow tubes, yield significant attenuation. Several components in the gasexchange system of IC-engines are based on arrays of narrow ducts and might haveunderestimated silencing capabilities. In particular the sound transmission properties of chargeair coolers (CAC) have so far gained interest from very few authors. In Paper D a detailedinvestigation of the acoustic properties of CACs is presented. As a result the first linearfrequency-domain model for CACs, which includes a complete treatment of losses in the narrowtubes and 3D effects in the connecting tanks, is proposed. Interesting low frequency dampingmost likely due to interaction between sound and turbulence is observed in the experimentaldata. A new numerical model that describes this dissipative effect in narrow tubes is suggestedin Paper E. Validation is carried out using experimental data from the literature. Finally, inPaper F the CAC-model presented in Paper D is updated with the new model for interactionbetween turbulence and acoustic waves proposed in Paper E. The updated model is shown toyield improved predictions.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xvi, 32 p.
Trita-AVE, ISSN 1651-7660 ; 2009:16
IC-engine, intake noise, gas dynamics, linear source data, frequency domain, 2-port, losses, air cleaner unit, filter paper, flow, FEM, BEM, charge air cooler, narrow tube
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-10549 (URN)
Public defence
2009-06-01, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 13:15 (English)
QC 20100723Available from: 2009-05-26 Created: 2009-05-26 Last updated: 2010-07-23Bibliographically approved

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