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Investigation of perforated mufflers and plates
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. (MWL)
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

 

 

Mufflers are used in for instance exhaust system of cars or trucks to reduce noise.

Perforated pipes are one of the main components of modern mufflers. To study acoustic properties of mufflers with perforated pipe is one of the main targets of this thesis. Furthermore, how flow is distributed along perforated pipes is critical for the acoustic prediction of mufflers since it controls the acoustic impedance of the perforate. Therefore another goal of the thesis is to investigate a simple flow model which can predict the flow distribution in perforated pipe mufflers. So called micro-perforated plates have a large potential to be applied in vehicle applications. To understand the acoustic properties of microperforated plates and their application in mufflers is another purpose of the thesis.

 

A set of typical perforated mufflers, through flow, plug flow and eccentric, were built and tested with and without flow. In this work three issues were studied: i) effects of perforations, ii) effects of higher order modes and iii) effects of the presence of a mean flow. The measurements were compared with numerical simulations using two commercial softwares the 1-D Boost linear acoustics tool and the 3-D FemLab tool.

 

A quasi-steady semi-analytical model is proposed to predict the grazing-bias flow in a perforated-pipe muffler at low Mach numbers for high Reynolds numbers based on the diameter of the perforation. Firstly two one-hole models are presented which are the small hole model and the large hole model. The next is to apply the one-hole model to the whole perforated pipe muffler. This model allows the prediction of the steady flow distribution through a muffler and the pressure drop of the muffler. The model was compared with experimental and numerical data from the literature.

 

Micro-perforated plates (MPP:s) can be subjected to both flow, high temperatures as well as high sound levels and the effect of this on the MPP impedance must be known. In the present work two types of MPP:s have been investigated: i) plates with circular holes and ii) plates with slit-shaped holes. Non-linear effects were investigated with both random noise and pure tone excitation and the results compared with models from the literature. The effect of a grazing mean flow was also investigated and based on the results correction terms for the MPP impedance are proposed. As an application of the work a new type of MPP muffler has been investigated. Based on numerical simulations performed a very efficient through flow

multi-chamber MPP muffler configuration was found. The performance of the new muffler was also verified by experiments.

 

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 19 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:06
Keyword [en]
sound, perforated, micro-perforated, muffler, flow, hole, impedance, model, experiment
Identifiers
URN: urn:nbn:se:kth:diva-10170OAI: oai:DiVA.org:kth-10170DiVA: diva2:209844
Presentation
2009-03-13, Room 40, Teknikringen 8, KTH MWL, 10:15 (English)
Opponent
Supervisors
Available from: 2009-03-31 Created: 2009-03-27 Last updated: 2010-10-13Bibliographically approved
List of papers
1. Experimental Investigation of Acoustic Properties of Mufflers with Perforated Pipes
Open this publication in new window or tab >>Experimental Investigation of Acoustic Properties of Mufflers with Perforated Pipes
2007 (English)In: 19th International Congress on Acoustics Madrid, Spain, September 2007, 2007Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-25215 (URN)
Conference
19th International Congress on Acoustics Madrid, Spain, September 2007
Note
QC 20101013Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2012-03-29Bibliographically approved
2. A Semi-analytical Model for Perforated Pipe Mufflers
Open this publication in new window or tab >>A Semi-analytical Model for Perforated Pipe Mufflers
2008 (English)In: Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics , 2008, 092407- p.Conference paper, Published paper (Refereed)
Abstract [en]

A quasi-steady semi-analytical model is proposed to predict the grazing-bias flow in a perforated-pipe muffler at low Mach numbers for high Reynolds numbers based on the diameter of the perforation. This model allows both the prediction of the steady flow distribution through a muffler and the prediction of the acoustical response of the perforated pipe in terms of the impedance. The model is compared with experimental and numerical data from the literature. The incorporation of the influence of the flow in this impedance allows predicting the global acoustical response of the muffler by means of a Finite Element Method solution of the Helmholtz equation, neglecting other convective effects. This procedure is tested for two extreme cases. Firstly we consider a through flow muffler consisting of an expansion chamber mounted axis-symmetrically around a perforated pipe. Secondly a plug flow muffler is considered, which is the same muffler but with a plug placed halfway along the perforated pipe, forcing the flow through the pipe perforations. In both cases the model predicts the transmission loss of the muffler within 1 dB for Strouhal numbers (based on the perforation diameter and main flow velocity) of order unity. The performance of the through flow muffler is essentially that of an expansion chamber without major contribution of flow effects. In the plug flow muffler the flow does significantly enhances the muffler performance, but this is at the cost of a significant static pressure loss.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2008
Keyword
Acoustical response, Convective effects, Expansion chamber, Extreme case, Flow distribution, Flow effects, Flowthrough, High Reynolds number, Low Mach numbers, Numerical data, Pipe mufflers, Plug flow, Quasi-steady, Semi-analytical model, Static pressure, Transmission loss
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-25217 (URN)2-s2.0-78249270781 (Scopus ID)9781563479397 (ISBN)
Conference
AIAA Conference, Vancouver, Canada, May, 2008
Note

QC 20101013

Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2014-10-10Bibliographically approved
3. Micro-Perforated Plates for Vehicle Applications
Open this publication in new window or tab >>Micro-Perforated Plates for Vehicle Applications
2008 (English)In: Proceedings of the 2008 Congress and exposition of noise control engineering, Inter-Noise 2008, 26-29 Oct, Shanghai, China, 2008Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:kth:diva-25220 (URN)
Conference
37th International Congress and Exhibition on Noise Control Engineering, Shanghai, China October, 2008
Note
QC 20101013Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2012-03-29Bibliographically approved

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