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  • 151.
    Tiikoja, Heiki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Rämmal, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lavrentjev, Jüri
    Dept. of Machinery, Tallin University of Technology, Tallin, Estonia.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Investigation of sound reflection from a hot and subsonic flow duct termination2012Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet vitenskapelig)
  • 152.
    Tiikoja, Heiki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Rämmal, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Investigations of automotive turbo-charger acoustics2011Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 4, nr 2, s. 2531-2542Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper an overview of recent experimental studies performed at KTH on the sound transmission and sound generation in turbochargers is presented. The compressor and turbine of the turbochargers are treated as acoustic active 2-ports and characterized using the unique experimental test facility established at KTH. The 2-port model is limited to the plane wave range so for higher frequencies the propagating acoustic power is estimated using an average based on pressure cross-spectra. A number of automotive turbochargers have been studied for a variety of operating conditions systematically selected from the compressor and turbine charts. The paper discusses the experimental procedures including special techniques implemented to improve the quality of the data. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are presented.

  • 153.
    Tiikoja, Heiki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Rämmal, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Sound transmission in automotive turbochargers2011Inngår i: Noise and Vibration Conference and Exhibition (SAE NVH 2011)Grand Rapids, Michigan, USA, May 2011, 2011Konferansepaper (Fagfellevurdert)
  • 154.
    Tiikoja, Heiki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231). KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Rämmal, Hans
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231). KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats E G
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231). KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231). KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Test-rig for complete acoustic characterization of turbochargers2010Inngår i: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this paper is to present description of a novel experimental facility designed and set up in KTH Cicero Centre for complete acoustic characterization of turbochargers. The facility is created to determine both the passive (scattering) and active (source) acoustic properties of automotive turbochargers. In this paper the currently most accurate experimental technique to determine the passive acoustic effect of the turbocharger is described. A detailed overview of the test-rig is given together with the mathematical procedures followed to obtain the acoustic 2-port data for turbochargers. The results, including transmission loss and scattering matrix elements, are presented for the compressor and turbine side of a typical automotive turbocharger working in a number of different operating conditions. The influence of the operating conditions on the passive acoustic effect of the device is studied and summarized.

  • 155. Vizzini, S.
    et al.
    Knutsson, M.
    Dybeck, M.
    Åbom, Mats
    KTH.
    Flow Noise Generation in a Pipe Bend2018Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2018-June, nr JuneArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noise generated by low Mach number flow in duct networks is important in many industrial applications. In the automotive industry the two most important are the ventilation duct network and the engine exhaust system. Traditionally, design is made based on rule-of thumb or slightly better by simple semi-empirical scaling laws for flow noise. In many cases, strong curvatures and local deviations from circular cross-sections are created due to outer geometry restrictions. This can result in local relatively high flow velocities and complex flow separation patterns and as a result, rule-of thumb and scaling law methods can become highly inaccurate and uncertain. More advanced techniques based on time domain modelling of the fluid dynamics equations together with acoustic analogies can offer a better understanding of the local noise generation, the propagation and interaction with the rest of the system. This investigation focuses on validating an SNGR numerical model to predict flow noise generation due to separation in a circular duct with a 90-degree bend carrying a flow lower than 0.3 Mach number. Experimental results are presented and compared to numerical simulations, based on a combination of steady computational fluid dynamics and the stochastic acoustic analogy by Lighthill, as well as semi-empirical models based two-ports.

  • 156. Wagih, M.
    et al.
    Elnady, T.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Analysis of duct networks at high frequencies using two-ports2013Inngår i: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life, OAL-Osterreichischer Arbeitsring fur Larmbekampfung , 2013, s. 5896-5905Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Duct Networks (e.g. HVAC) should be carefully designed to maintain certain pressure drop, flow rate and acceptable noise levels. To accurately analyze the acoustics in a duct network in the high frequency region, the following mechanisms need to be modeled: The sound power injected into the network by sound sources (e.g. Fans), the flow noise generated in different parts in the network (e.g. junctions), and the noise reduction across different parts of the network. Traditionally only transmission of sound power with no reflection is considered in standards, e.g., ASHRAE or VDI, for analyzing noise in HVAC systems. In this paper, a more general approach is considered based on dividing the duct network into two-port elements where each element can be described by a 2×2 scattering matrix. The state variables are taken as acoustic power flow in the up/downstream directions. Junctions are described by multi-ports depending on the number of elements connected to the junction. A source vector is added to each element and junction to handle sound power injection by fans or other aeroacoustic sources. The advantage of this approach is that the same formalism (based on two-port network theory) can be used to analyze both low frequency range and flow distribution / pressure drop as well as the high frequency range. The two-port power based formulation was validated against a detailed HVAC example in VDI 2081: Part 2.

  • 157.
    Wagih, Mina
    et al.
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, Cairo, Egypt..
    Elnady, Tamer
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, Cairo, Egypt..
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Ultraljud. Royal Inst Technol KTH, Marcus Wallenberg Lab Sound & Vibrat Res, Stockholm, Sweden..
    Analysis of Flow and Sound Propagation in HVAC Ducts Using Two-Port Network Theory2014Inngår i: ASHRAE TRANSACTIONS 2014, VOL 120, PT 2, AMER SOC HEATING, REFRIGERATING AND AIR-CONDITIONING ENGS , 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Duct Networks (e.g. HVAC) are designed to maintain flow rates at acceptable noise levels. To accurately analyze the acoustics in a duct network in the high frequency region, the following mechanisms need to be modeled: The sound power injected into the network by sound sources (e.g. Fans), the flow noise generated in different parts in the network (e.g. junctions), and the noise reduction across different parts of the network. Traditionally only transmission of sound power with no reflection is considered in standards, e.g., ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) or VDI (The Association of German Engineers), for analyzing noise in HVAC systems. In this paper, a more general approach is considered based on dividing the duct network into two-port elements where each element can be described by a 2x2 scattering matrix. The state variables are taken as acoustic power flow in the up/downstream directions. Junctions are described by multiports depending on the number of elements connected to the junction. A source vector is added to each element and junction to handle sound power injection by fans or other aero-acoustic sources. The advantage of this approach is that the same formalism (based on two-port network theory) can be used to analyze the low frequency range, the flow distribution and the pressure drop across each network path as well as the high frequency range. This two-port power based formulation was earlier validated against a detailed HVAC example in VDI 2081 part2. In this paper, it is validated against a real-life case study and compared with the measurements.

  • 158.
    Wallin, Hans Petter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Carlsson, Ulf
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Glav, Ragnar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Hildebrand, Robert
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Sound and vibration2010 (oppl. 2., rev. uppl.)Bok (Annet vitenskapelig)
  • 159. Williams, P.
    et al.
    Kirby, R.
    Hill, J.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Malecki, C.
    Reducing low frequency tonal noise in large ducts using a hybrid reactive-dissipative silencer2018Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 131, s. 61-69Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noise generated by fans or turbines normally consists of a combination of narrow and broadband noise. To lower transmitted noise levels, it is attractive to use a combination of reactive and dissipative elements. However, this approach presents a number of challenges for larger systems. This is because reactive elements are commonly placed around the duct circumference where they are normally only effective up to the frequency at which the first higher order mode cuts on in the duct. For larger systems, this means that reactive elements work only in the low, and often very low, frequency range, whereas dissipative elements, which are distributed across the duct cross-section, generally work well in the medium to high frequency range. This can cause noise problems in the low to medium frequency range in larger systems. This article presents an alternative approach for delivering noise attenuation over the low to medium frequency range that is suitable for application in larger duct systems. This approach takes advantage of those splitter silencer designs commonly used in larger systems to integrate a reactive element into the splitter design. This delivers a hybrid splitter that uses a combination of dissipative and reactive elements so that the reactive element partitions the main airway. This has the advantage of introducing a quasi-planar transverse sound pressure field for each resonator in the low to medium frequency range, including frequencies above the first cut-on. It is demonstrated using predictions and measurements taken for a number of example silencers, that this approach enables reactive elements to work over an extended low to medium frequency range, including at frequencies above the first cut-on mode in the main duct. Accordingly, it is shown that a hybrid dissipative-reactive splitter design is capable of delivering improved levels of attenuation in the crucial low to medium frequency range.

  • 160. Williams, P. T.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Kirby, R.
    Hill, J.
    The influence of higher order incident modes on the performance of a hybrid reactive-dissipative splitter silencer2017Inngår i: Proceedings of Meetings on Acoustics, Acoustical Society of America , 2017, nr 1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A hybrid reactive-dissipative splitter silencer offers the potential to attenuate turbomachinery noise over a wide frequency range, including the problematic low to medium frequencies. This article uses a theoretical model to investigate the performance of a hybrid parallel baffle silencer for different complex incident sound fields. This includes an incident sound field with equal modal energy density, as well as the excitation of individual higher order modes. It is shown that provided horizontal and vertical partitions are used in the reactive element, the sound attenuation performance of the reactive chamber under complex incident sound fields is equivalent to that obtained using plane wave excitation over the frequency range of interest. Furthermore, it is demonstrated that the reactive elements work at frequencies above the first cut-on mode in the inlet duct, and so they are capable of extending sound attenuation into the low to medium frequency range. This delivers an efficient hybrid silencer design that is suitable for use in power generation applications, such as gas turbine exhaust systems. 

  • 161. Xianghai, Q.
    et al.
    Lin, D.
    Xiaodong, J.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A combined design method for optimal acoustic treatment of annular aeroengine inlet based on cremer impedance2018Inngår i: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, Vol. 2, s. 1248-1255Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A combined design method of impedance of acoustic nacelle is developed based on the Cremer impedance. First, the Cremer method is further extended to provide the theoretical optimum impedance for infinite uniform annular ducts in the presence of a single azimuthal mode and plug flow. Then, with the Cremer impedance being the initial value, the searching optimization based on a finite element sound propagation model is conducted to determine the impedance for maximizing noise reduction under the conditions of nearly actual duct geometry and flow. A design case of impedance of a typical aeroengine inlet is used to evaluate the method. The TL contour against impedance indicates that the combined design can avoid the local solution and find successfully the globally optimum impedance, thereby leading to the maximum sound attenuation. Additionally, the Cremer impedance is quite close to the final optimum impedance in this case, thereby providing not only a good initial impedance but also a proper searching space for the search optimization. Therefore, the combined design method is of high efficiency and accuracy.

  • 162. Zhang, Z.
    et al.
    Kabral, R.
    Nilsson, B.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Revisiting the cremer impedance2017Inngår i: Proceedings of Meetings on Acoustics, Acoustical Society of America , 2017, nr 1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In a classical paper (Acustica 3, 1953) Cremer demonstrated that in a rectangular duct, with locally reacting walls, there exits an impedance (”the Cremer impedance”) that maximizes the propagational damping for the lowest mode. Later (JSV 28, 1973) Tester extended the analysis to include a plug flow and ducts of both circular and rectangular cross-section. One limitation in the work of Tester is that it simplified the analysis of the effect of flow only considering high frequencies or well cut-on modes. This approximation is reasonable for large duct applications, e.g., aero-engines, but not for many other cases of interest. Kabral et al. (Acta Acustica united with Acustica 102, 2016) removed this limitation and investigated the’exact’ Cremer impedance for circular ducts including flow effects. As demonstrated in that paper the exact solution exhibits some special properties at low frequencies, e.g., a negative real part of the wall impedance. In this paper the exact Cremer impedance is further analyzed and discussed. Also, the exact solution for rectangular ducts is presented. 

  • 163.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    The Cremer Impedance: An Investigation of the Low Frequency BehaviorManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The Cremer impedance, first proposed by Cremer (1953) and then extended by Tester (1973), is supposed to give the maximum propagation damping in an infinitely long waveguide. Previous works including a uniform grazing flow have shown negative resistance in the low frequency range for both circular and 2-D rectangular waveguides, i.e., implying an active boundary. In order to further analyze the low frequency behaviour of the Cremer impedance, especially the negative resistance, two investigations are conducted in the current work. First, the previously used Ingard-Myers boundary condition is replaced by the Brambley boundary condition with the introduction of a thin inviscid boundary layer, and results obtained with the two boundary conditions are compared to see the effect of a sheared flow. The frequency range where the two boundary conditions can be applied is also analyzed. Second, discussions regarding the validity of the low frequency result in both the up- and downstream directions from the perspective of mode-merging are presented. This analysis is further extended from the fundamental mode to higher order modes in the frequency range where they are ‘just cut-on’.

  • 164.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    The Cremer impedance: An investigation of the low frequency behavior2019Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 459, artikkel-id 114844Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Cremer impedance concept based on mode merging is one method that can substantially improve the axial damping in a waveguide. Previous works on the Cremer impedance including a uniform grazing flow have exhibited unexpected phenomenon such as negative resistance in the low frequency range. The current paper is a continuation of earlier works by the authors to extend the investigation of the Cremer impedance with a focus on the low frequency range. Two independent investigations from the perspective of boundary layer effects and mode merging patterns are conducted to better understand the low frequency behavior of the Cremer impedance.

  • 165.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lin, D.
    Xiaodong, J.
    Investigation of the 'exact' cremer impedance2018Inngår i: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, s. 1810-1817Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Cremer impedance, first proposed by Cremer (Acustica 3, 1953) and then improved by Tester (JSV 28, 1973), refers to the locally reacting boundary condition that can maximize the attenuation of a certain acoustic mode in a uniform waveguide. One limitation in Tester's work is that it simplified the analysis on the effect of flow by only considering high frequencies or the 'well cut-on' modes. This approximation is reasonable for large duct applications, e.g., aero-engines, but not for many other cases of interest such as the vehicle intake and exhaust systems. A recent modification done by Kabral et al. (Acta Acustica united with Acustica 102, 2016) has removed this limitation and investigated the 'exact' solution of Cremer impedance, which reveals an appreciable difference between the exact and classic solution in the low frequency range. A measurement campaign is here carried out to experimentally demonstrate such difference. In addition, the exact solution is found to exhibit some special properties at very low frequencies, e.g., a negative resistance. One can question if this negative resistance is physically correct or an artefact of the assumption of a plug flow profile and the use of the so-called Ingard-Myers boundary condition. To investigate this the Cremer solution is here extended to the case with a more general and realistic flow profile, using a modified version of the Ingard-Myers condition suggested by Brambley (AIAA J 49(6), 2011).

  • 166.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Tiikoja, Heiki
    KTH.
    Peerlings, Luck
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Experimental Analysis on the 'Exact' Cremer Impedance in Rectangular Ducts2018Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2018-June, nr JuneArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cremer impedance, first proposed by Cremer (Acustica 3, 1953) and then improved by Tester (JSV 28, 1973), refers to the locally reacting boundary condition that can maximize the attenuation of a certain acoustic mode in a uniform waveguide. One limitation in Tester's work is that it simplified the analysis on the effect of flow by only considering high frequencies or the 'well cut-on' modes. This approximation is reasonable for large duct applications, e.g., aero-engines, but not for many other cases of interest, with the vehicle intake and exhaust system included. A recent modification done by Kabral et al. (Acta Acustica united with Acustica 102, 2016) has removed this limitation and investigated the 'exact' solution of Cremer impedance for circular waveguides, which reveals an appreciable difference between the exact and classic solution in the low frequency range. Consequently, the exact solution can lead to a much higher low-frequency attenuation level. In addition, the exact solution is found to exhibit some special properties at very low frequencies, e.g., a negative resistance. In this paper, liners designed on the basis of the exact solution are tested and the difference between the exact and classic solution in the low frequency range (not low enough to go into the negative resistance region) is experimentally investigated.

  • 167.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Tiikoja, Heiki
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Experimental analysis of whistle noise in a particle agglomeration pipe2018Inngår i: INTER-NOISE 2018 - 47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering, Institute of Noise Control Engineering , 2018Konferansepaper (Fagfellevurdert)
    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.

  • 168.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    ‘Double-’ and ‘Triple-root’ Cremer Impedancefor a Rectangular Duct with Opposite Lined WallsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    To achieve high low frequency damping in an infinitely long double-lined rectangular duct with zero mean flow, the optimization of axial sound attenuation in the sense defined by Cremer (i.e., using the ‘Cremer impedance/solution’ concept) is examined for the fundamental mode. Two double-root Cremer impedance solutions that merge a mode pair into a single mode are presented. Different mode-merging patterns due to symmetry are found for these two solutions. As an extension, two triple-root Cremer impedance solutions (including one with a negative resistance) that merge three modes are also provided by extending the optimum condition proposed by Cremer. The two triple root solutions are theoretically advantageous in damping compared with the double root solutions, and the advantage is explained from the perspective of mode-merging.

  • 169.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Katoshevski, D.
    Particle Number Reduction in Automotive Exhausts Using Acoustic Metamaterials2017Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 10, nr 4, s. 1566-1572Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Air pollution caused by exhaust particulate matter (PM) from vehicular traffic is a major health issue. Increasingly strict regulations of vehicle emission have been introduced and efforts have been put on both the suppression of particulate formation inside the engine cylinders and the development of after-treatment technologies such as filters. With modern direct injected engines that produce a large number of really small sub-micron particles, the focus has increased even further and now also includes a number count.The problem of calculating particle trajectories in flow ducts like vehicle exhaust systems is challenging but important to further improve the technology. The interaction between particles and oscillating flows may lead to the formation of particle groups (regions where the particle concentration is increased), yielding a possibility of realizing particle agglomeration. The oscillating flow may simply be hydrodynamic or as assumed here: the flow oscillations are created by sound propagation rather than hydrodynamic approaches. An analysis is presented which gives the relationship between the speed of sound, the mean flow velocity and the amplitude of the acoustic particle velocity for particle agglomeration to be feasible. It is shown that it can be achieved if the convective speed of sound is reduced to the same order as the mean flow velocity. It is therefore suggested to use the so-called acoustic metamaterials, which can help control, direct and manipulate sound waves. At this stage a phenomenological 1D model is used for the analysis, which allows the authors to build an understanding of the effect of the sound waves and flow oscillations on particle motion and paves the way for further analysis on particle agglomeration.

  • 170. Zhou, J.
    et al.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Study of thermoacoustic engine for automotive exhaust waste heat recovery2019Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2019-April, nr AprilArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the travelling-wave thermoacoustic engine (TAE) and its application for recovery of waste heat from automotive exhaust systems is investigated. The aim is to give some insight into the potential, but also limitations of the technique for practical applications. This includes packaging, physical boundary conditions as heating and cooling available, but also system perspectives as influence of legislative drive cycles and degree of hybridization. First, the travelling-wave TAE is described as a low-order acoustic network in the frequency domain. Models, including non-linear effects, are set up for every component in the network to describe the propagation and dissipation of acoustic waves. For a TAE with looped structure, the continuity of pressure and volumetric velocity is employed to determine the saturation pressure, as well as the stable operating point. These models are validated against experimental data available in the literature [1]. This is an engine designed for high-temperature application, but is well documented and yields a good reference for the models and to further the understanding of the TAE. Next, an optimized design for a system to be adapted to the operating conditions typical for heavy-duty systems is studied and proposed. No actual physical prototype has been built and verified, but the design is based on, and is of the same efficiency, as machines that have been reported in the literature. The proposed design and the original TAE are then used to discuss the practical implementation for heavy- and light-duty vehicles on a system level. To improve the utilization of the available exhaust waste heat, a configuration of system heat exchangers combining a self-circulating loop with multiple TAE modules is preliminarily studied. Further research for this configuration is needed for practical implementation although current simulation results are encouraging.

  • 171.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Acoustic multi-ports with application to duct acoustics2010Inngår i: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 5, 2010, s. 3930-3942Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper the development of multi-port models to describe linear acoustic problems in ducts with flow is presented. From an engineering point of view this field covers many important applications ranging from ventilation ducts in vehicles or buildings to intake/exhaust ducts on ICengines and power plants. Historically the use of multi-port models for ducts started in the 1920's, when the four-pole (2-port) filter models used by electrical engineers were applied to analyse transmission of low frequency 1D (plane) waves with application to automotive mufflers. An important step was then taken in 1971, when Cremer presented the idea that such "black box" models can be applied to describe aerodynamically generated sound in ducts. This implies that any fluid machine or unsteady flow process can be modelled as a "black box", with a "passive part" that describes how incident waves are scattered and an "active part" that describes the sound generation. The active part is normally assumed independent of the acoustic state, which makes the "black box" or acoustic multi-port model consistent with Lighthills acoustic analogy.

  • 172.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Method for reducing noise of a high power combustion engine2003Patent (Annet (populærvitenskap, debatt, mm))
  • 173. Åbom, Mats
    New measurement and control approach for refiners and beaters2001Patent (Annet (populærvitenskap, debatt, mm))
  • 174. Åbom, Mats
    Sensor arrays in acoustic spectroscopy2001Patent (Annet (populærvitenskap, debatt, mm))
  • 175.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Allam, Sabry
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Dissipative silencers based on micro-perforated plates2013Inngår i: SAE Technical Papers, 2013, Vol. 6Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Micro-perforated plates (MPP:s) can be defined as a perforated plate where the hole impedance is dominated by viscous losses. This will always be true for sufficiently low frequencies or small holes. In addition for a standard MPP the perforation ratio is chosen so that the normalized acoustic resistance is between 1-2, which yields optimum damping for incident plane waves. Historically MPP:s have been used as panel absorbers to reduce reflections in rooms and enclosures. More recently the potential for machinery and vehicle applications has come into focus, e.g., dissipative exhaust silencers. Some advantages offered by a MPP solution, when compared to traditional dissipative silencers, are that it can reduce the weight and the problem with fibre breakout. In this paper the work on cylindrical MPP dissipative silencers at KTH is summarized. One important question being how an optimum damping is achieved, for a certain frequency band and for a given volume (length & area ratio) of the silencer.

  • 176.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Allam, Sabry
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Industrial Education College, Cairo, Egypt .
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Aero-acoustics of flow duct singularities at low mach numbers2006Inngår i: Collection of Technical Papers - 12th AIAA/CEAS Aeroacoustics Conference, 2006, s. 3708-3717Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper describes the application of an acoustic 2-port model to describe flow generated noise in ducts. An experimental procedure that enables determination of both the passive (the scattering matrix) as well as the active (source) 2-port data is described. The method is applied to investigate the aero-acoustics of an orifice plate in a duct. The passive data is compared with a simple quasi-stationary model and the active part is analyzed using a scaling law procedure, based on the assumption of a compact dipole source.

  • 177.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH-Centre for Sustainable Aviation.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH-Centre for Sustainable Aviation.
    Ulfvengren, Pernilla
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Industriell Management. KTH-Centre for Sustainable Aviation.
    Air traffic management and noise2018Inngår i: INTER-NOISE 2018 - 47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering, Institute of Noise Control Engineering , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With the steady increase of air traffic the need for developing sustainable aviation increases as well. To meet this need, the Swedish Transport Administration and KTH Royal Institute of Technology have established a Centre for Sustainable Aviation. In a global perspective, aviation research focuses on meeting future capacity needs for increased travel and at the same time achieve sustainability with reduced environmental impact and sustained or increased safety. This paper describes four on-going projects, as examples of the variety of research that may contribute to a sustainable society in both shorter and longer terms as well as both in a local and in an international perspective. Initially the centre will apply and direct existing knowledge towards noise abatement initiatives in aviation. I the long-term perspective the research will contribute to knowledge on a broader spectrum of sustainability aspects of aviation.

  • 178.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Kabral, Raimo
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Turbocharger noise - Generation and control2014Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An important part of modern engine design is the concept of downsizing where a key role is carried by the charging devices. These devices are effective aero-acoustic sources forming a coupled acoustic system with the connected flow-channel components. At KTH a unique test facility for determination of the complete acoustic Two-port for turbochargers has been built. Using this facility both the passive (transmission & reflection) as well as the active (sound generation) data for turbochargers can be measured at a given operating point. One important issue which has been studied in detail using this data is the coupling between the aerodynamic and acoustic fields close to "surge". In addition, the control of compressor noise is an increasing concern. For instance heavy duty diesels and light duty engines with screw (roots) compressors can create strong charging harmonics well below 10 kHz. The standard noise control solution for these cases is to build a series of resonators. As an alternative KTH has developed a novel compact and very efficient silencer in the form of an expansion chamber with locally reacting cavities. The cavities consists of a micro-perforated plate in front of a closed air volume. The micro-perforate and volume are then chosen so that the cavity impedance equals the so called Cremer impedance at a target frequency. This ensures a very high damping at one frequency (hundreds of dB/m) and using this concept compact silencers with a damping higher than 30 dB in octave around the target frequency can be designed.

  • 179.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Can acoustic multi-port models be used to predict whistling2010Inngår i: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, s. 2010-4009-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In duct aeroacoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aeroacoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this kind of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles. The implication of these ideas is that multi-port models can be used to analyze amplification of sound and whistling.

  • 180.
    Åbom, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kierkegaard, Axel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On the use of linear aero-acoustic methods to predict whistling2009Inngår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, s. 2406-2413Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In duct aero-acoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aero-acoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this type of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles.

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