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Experimental analysis of whistle noise in a particle agglomeration pipe
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0001-7898-8643
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0002-8474-8563
2018 (English)In: INTER-NOISE 2018 - 47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering, Institute of Noise Control Engineering , 2018Conference paper, Published paper (Refereed)
Abstract [en]

A self-sustained sound, more usually known as a whistle, refers to a distinct tonal noise created due to the interaction between the sound and flow field. When a positive feedback loop is formed between the two fields, the energy in the mean flow will be transferred into the sound wave, thus giving rise to a whistle. In engineering practice, whistles are destructive as they can produce high sound and vibration levels and may result in risk for mechanical failures. In this work, a flow-related high level tonal noise was found during a measurement on a particle agglomeration pipe, which is a quasi-periodic corrugated structure designed for the exhaust system of heavy-duty trucks. The purpose of the pipe is to enhance particle agglomeration to increase the size of exhaust gas particles. To investigate the origin of the detected tonal noise additional measurements were carried out. Based on the measurement result, the aero-acoustic coupling in the agglomeration pipe was analyzed, revealing that the pipe has a large potentiality to amplify the incident sound power in the presence of a mean flow. Furthermore, the Nyquist stability criterion was applied to confirm the existence of exponentially growing modes in the system at certain conditions.

Place, publisher, year, edition, pages
Institute of Noise Control Engineering , 2018.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-241859ISI: 000456356800019Scopus ID: 2-s2.0-85059372519OAI: oai:DiVA.org:kth-241859DiVA, id: diva2:1282683
Conference
47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering, INTER-NOISE 2018, Marriott Magnificent Mile DowntownChicago, United States, 26 August 2018 through 29 August 2018
Note

QC 20190122

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-05-14Bibliographically approved
In thesis
1. Optimal damping and slow sound in ducts
Open this publication in new window or tab >>Optimal damping and slow sound in ducts
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis is dedicated to expanding knowledge on two duct acoustic issues including: 1) the optimal damping of low frequency sound and 2) the development and application of ‘slow sound’.

To address the first issue, the ‘Cremer impedance’ proposed more than half a century ago has been revisited and further developed. The original motivation is to extend the concept from large duct applications, such as aero-engines, to low frequency applications including vehicle intake and exhaust or cooling and ventilation systems. This leads to the derivation of the ‘exact’ solution of the Cremer impedance for single-lined rectangular ducts valid in the low frequency range in the presence of a ‘plug’ flow. A substantial improvement in the low frequency damping is achieved with the exact solution and a measurement campaign is carried out to validate this.

However, for both circular and rectangular ducts (including single-lined and double-lined types) the exact solution of the Cremer impedance has a negative real part in the low frequency range. This indicates that an active boundary is required to provide the optimal damping. Two investigations on the negative resistance are conducted. First, the ‘plug’ flow is replaced by a sheared flow by changing the boundary condition in the optimization model. With this modification, the Cremer impedance is recalculated and the negative resistance is still found in most cases, demonstrating that the negative resistance is not necessarily an artefact of the boundary condition. Second, since the Cremer impedance is based on mode-merging, a mode-merging analysis is carried out. The merging result shows that the downstream results are always valid, but some of the upstream results in the low frequency range are invalid in the sense that unexpected mode pairs merge, and the corresponding damping is smaller than expected. This finding is true for both the fundamental mode and higher order modes.

Regarding the second issue, ‘slow sound’ or sound with a much reduced ‘phase velocity’ is investigated using a resonant periodic system in the low frequency range. This can be seen as an acoustic metamaterial where sound propagates at a much smaller-than-normal speed around its resonance frequency. Following a hydrodynamic particle agglomeration model, the slow sound is applied to manipulate the distribution of small particles in the vehicle exhaust system. Although in principle this acoustic agglomeration method can work, it will only be efficient if the wave damping in the metamaterial is kept small. 

Abstract [sv]

Denna avhandling har till syfte att öka kunskapen om akustiska problem i kanaler, inklusive: 1) optimal dämpning av lågfrekvent ljud och; 2) utveckling och tillämpning av ‘slow sound’.När det gäller det första problemet, har ‘Cremer-impedansen’, som föreslogs för mer än ett halvt sekel sedan studerats och vidareutvecklats. Detta möjliggör nya tillämpningar svarande mot lågfrekvent ljud som insugnings- och avgassystem för fordon samt ventilationssystem. En ‘exakt’ lösning av Cremer-impedansen för rektangulära kanaler med en ljuddämpande vägg giltig i lågfrekvensområdet har härletts. En väsentlig förbättring av lågfrekvent dämpning har uppnåtts med denna lösning vilket även validerats med mätningar.Emellertid har den exakta lösningen av Cremer-impedansen en negativ realdel (‘resistans’) i lågfrekvensområdet, vilket betyder att en aktiv väggbeklädnad är nödvändig för att åstadkomma optimal dämpning. Två undersökningar av den negativa resistansen har genomförts för att studera om dessa lösningar är realiserbara. I den första ändrades randvillkoret för att inkludera gränsskikt i strömningen. Resultatet visade att negativ resistans erhålls i de flesta fall även med det modifierade randvillkoret. I den andra studerades lösningens giltighet i det komplexa vågtalsplanet. Resultatet visade att lösningen nedströms alltid är giltig medan vissa lösningar uppströms i lågfrekvensområdet är ogiltiga. Detta resultat gäller i princip för alla vågor eller moder i en kanal.När det gäller det andra problemet undersöktes möjligheterna att skapa ‘slow sound’, dvs ljud som utbreder sig mycket långsammare än normalt, genom att utnyttja ett resonant periodiskt system i en kanal i lågfrekvensområdet. Detta kan ses som ett s.k. akustiskt metamaterial och kan nyttjas för att med hjälp av starka ljudvågor påverka små partiklar som tvingas att kollidera och bli större. En studie om denna metod för sammanslagning av partiklar (‘particle agglomeration’) kan nyttjas för avgasrening har genomförts. Metoden är teoretiskt möjlig men begränsad av att tekniken för att skapa ‘slow sound’ inte bara saktar ned ljudvågen utan även dämpar dess amplitud och därigenom minska ljudvågens påverkan på partiklar.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 75
Series
TRITA-SCI-FOU ; 2019:22
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-251443 (URN)978-91-7873-176-3 (ISBN)
Public defence
2019-06-04, F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC20190514

Available from: 2019-05-14 Created: 2019-05-14 Last updated: 2019-05-14Bibliographically approved

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Zhang, ZheÅbom, MatsBodén, Hans

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