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  • 51.
    Glav, R
    et al.
    KTH, Tidigare Institutioner, Farkostteknik.
    Bodén, Hans
    KTH, Tidigare Institutioner, Farkostteknik.
    Åbom, Mats
    KTH, Tidigare Institutioner, Farkostteknik.
    An acoustic model for automobile catalytic converters1988Konferansepaper (Fagfellevurdert)
  • 52.
    Glav, R
    et al.
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Åbom, M
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    A general formalism for analysing acoustic 2-port networks1997Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 202, nr 5, s. 739-747Artikkel i tidsskrift (Fagfellevurdert)
  • 53. Glav, Ragnar
    et al.
    Costa, A.
    Åbom, Mats
    Application of the folded resonator2003Inngår i: Proceedings of the Tenth International Congress on Sound and Vibration, 2003, s. 3203-3210Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A folded side-branch resonator has been designed and tested on a heavy truck. The design procedure is based on numerical simulations of the complete exhaust line and cold flow measurements of resonator inlet resistance and end-correction. A reduction in exhaust noise of as much as 7dB relative to the standard exhaust system shows the potential of the suggested technique to handle low frequency problems without increased volume or backpressure.

  • 54. Glav, Ragnar
    et al.
    Nygård, Stefan
    Åbom, Mats
    Effektiva beräkningsmetoder för akustisk modellering av ljuddämparsystem. D. 2: slutrapport1999Rapport (Annet vitenskapelig)
  • 55. Glav, Ragnar
    et al.
    Regaud, Pierre-Luc
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Åbom, Mats
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Study of a folded resonator including the effects of higher order modes2004Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 273, nr 4-5, s. 777-792Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a derivation of the 2-port matrix for a folded quarter-wave side-branch resonator including higher order modes but neglecting flow interaction effects. The model is restricted to coaxial geometries and two-folds. The derivation is based on the mode matching technique and is verified by measurements done on prototypes. A notable result from these experiments is the effects of a slit-like leakage close to a rigid wall. A parametrical study finally investigates the influence of various lengths and area ratios of the resonator resulting in a set of design rules.

  • 56.
    Glav, Ragnar
    et al.
    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.
    Fairbrother, Robert
    AVL.
    Acoustic modelling for practical intake and exhaust system design2006Konferansepaper (Fagfellevurdert)
  • 57.
    Guo, Ying
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Allam, Sabry
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Micro-Perforated Plates for Vehicle Applications2008Inngår i: Proceedings of the 2008 Congress and exposition of noise control engineering, Inter-Noise 2008, 26-29 Oct, Shanghai, China, 2008Konferansepaper (Fagfellevurdert)
  • 58.
    Guo, Ying
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Dolinar, Andreas
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Allam, Sabry
    Experimental Investigation of Acoustic Properties of Mufflers with Perforated Pipes2007Inngår i: 19th International Congress on Acoustics Madrid, Spain, September 2007, 2007Konferansepaper (Fagfellevurdert)
  • 59.
    Holmberg, Andreas
    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.
    The Error Suppression of an Experimental Over-Determination of In-Duct Flow Noise Sources2010Inngår i: 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, June 2010, 2010, s. 1-19Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The full aeroacoustic two-port measurement procedure in flow ducts involves the determination of a scattering matrix and a source term. In this paper, the improved error suppression of a recently developed over-determination technique for the source is investigated. By inducing disturbances in the reflection coefficients it is shown that by applying the over-determination the accuracy is improved. For errors introduced via the scattering matrix the results are identical regardless of method applied. From measurements it is shown that random errors in the microphone data are better suppressed using the over-determination method. While this is true for bias errors due to external sound sources as well, the accuracy is unsatisfying when the external source generated sound is more than about 3 dB louder than that of the two-port source.

  • 60.
    Holmberg, Andreas
    et al.
    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).
    Karlsson, Mikael
    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 teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2015Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 340, s. 152-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scattering matrices are determined experimentally and used to study the low amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.

  • 61.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mikael, Karlsson
    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. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows: an experimental investigationInngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet vitenskapelig)
  • 62.
    Holmberg, Andreas
    et al.
    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 Marcus Wallenberg Laboratoriet.
    Accurate experimental two-port analysis of flow generated sound2011Inngår i: Sound & vibration, ISSN 1541-0161, Vol. 330, nr 26, s. 6336-6354Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    In the study of in-duct aero-acoustic phenomena two-port analysis based upon in-duct measurements has become an important method for the plane wave region. However already at moderate Mach numbers (0.2 - 0.3) the errors in the results can be hard to suppress. Ways of dealing with this includes the use of over-determination methods and methods of obtaining more accurate wave numbers. In this paper different methods for the determination of the source data and the scattering matrix are evaluated. For the source data in the form of a cross spectrum matrix an over-determination method is introduced. In addition, a method of obtaining the mean Mach number from experimentally determined wave numbers is described.

    In order to evaluate the methods measurements are conducted at a mean Mach number of 0.2 for two test cases – an empty duct and a mixer plate inside the duct. The main improvements in the scattering matrix results are achieved by discarding measurements from an abundant set, based upon the measured coherence between excitation and fluctuating pressures. For the source part, it is shown that the error in the magnitude of the source cross spectrum matrix can be significantly suppressed by having additional (> 2) reference microphones on each side of the two-port.

    The mean Mach number obtained from an experimentally determined wave number is observed to yield more accurate scattering matrix results in both phase and magnitude, than that based upon flow velocity measurements at one point and an assumed flow profile.

  • 63.
    Holmberg, Andreas
    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). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    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). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, M.
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimentally determined scattering matrices are used to study the low-amplitude interaction between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. Common for all flow combinations is that waves incident on the junction at the downstream side are only attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in-flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T junctions of circular ducts, the interaction is stronger for rectangular duct junctions.

  • 64. Hynninen, A.
    et al.
    Turunen, R.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. 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. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Acoustic source data for medium speed IC-engines2011Inngår i: 18th International Congress on Sound and Vibration 2011 (ICSV 18), 2011, s. 811-818Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. Number of studies has been published earlier on the low frequency in-duct exhaust noise of high speed engines. The goal of the present study is to investigate the medium speed IC-engine acoustic source characteristics numerically and experimentally not only in the low frequency - plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multi-load measurements using a one-dimensional process simulation code. The engine model used in the one-dimensional process simulations was validated with measurements. In this study, it is shown that the low frequency in-duct exhaust noise of a medium speed IC-engine can be predicted quite accurately by using a onedimensional process simulation code. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods. According to this study, using the simple cross spectra averaging method instead of two microphone method to estimate the induct downstream acoustic power of medium speed IC-engine exhaust noise seems promising. The simulation of the high frequency exhaust noise is beyond this study.

  • 65. Hynninen, A.
    et al.
    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).
    Acoustic two-port simulation model for the particle oxidation catalyst (POC®)2014Inngår i: INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The reduction of the exhaust noise from internal combustion engine (IC-engine) is mainly managed by proper silencer design, while less attention is paid to the acoustic performance of the after treatment devices (ATD). It is known from the earlier studies, that the transmission loss of a typical ATD unit can be quite significant. An ATD unit for diesel engines is classically assembled from several specific parts such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POC®). The substrate used in the POC-X type filter consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. In this paper an acoustic two-port simulation model for POC-X is sought starting from the classical Kirchhoff solution for prediction of the acoustic wave attenuation in narrow channels. According to experimental studies, correction factors to the narrow channel two-port model are proposed.

  • 66. Hynninen, A.
    et al.
    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).
    Estimating the high frequency in-duct sound power using sound pressures at the duct wall2013Inngår i: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, s. 2553-2559Konferansepaper (Fagfellevurdert)
    Abstract [en]

    When studying the acoustic wave propagation in a Channel, the frequency range can be divided to the low frequency plane wave range and to the high frequency range with non-plane waves. In the low frequency range the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct the lower the frequency limit of the non-plane waves. Therefore taking into account also the three-dimensional acoustic wave propagation is important especially when considering the duct systems used in large structures, e.g., medium speed internal combustion engines (IC-engines), fans, or compressors. Harsh environment and unmovable structures restrict the use of standardized noise measuring methods. To characterize the medium speed IC-engine exhaust noise in situ, the in-duct sound pressures are measured using wall mounted transducers. Then the source sound power is estimated from the propagating sound pressures, which is the power based approach. The power based approach is only valid in frequency averaged sense and therefore the source power must be defined in one-third octave frequency bands, for example. One way to estimate the source sound power in the high frequency range, is to extend the classical plane wave formulation by defining the one-third octave frequency band weighting factors for different excitation types. The aim of this study is to define these weighting factors using finite element method (FEM) simulations of a test duct with non-reflecting terminations. The sound pressures at the duct wall were compared to the sound pressures at the duct end for randomized multi-modal excitations. From statistics, the one-third octave band weighting factors and their reliability were estimated.

  • 67. Hynninen, A.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Procedure to estimate the acoustic performance of the particle oxidation catalyst poc® with low Mach-number flows2015Inngår i: INTER-NOISE 2015 - 44th International Congress and Exposition on Noise Control Engineering, The Institute of Noise Control Engineering of the USA, Inc. , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The main component for the reduction of the exhaust noise from internal combustion engine (IC-engine) is the properly designed silencer. In addition, the acoustic performance of the after treatment devices (ATD) has gained interest as noise reduction components. Typically an ATD for diesel engines is assembled from components such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POCR ). The POC R substrate studied in this paper is of type POC-X, which consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. According to earlier studies the acoustic behaviour of the filter with negligible flow can be estimated with reasonable accuracy starting from the Kirchhoff solution. It was also concluded earlier that treating the filter as an acoustic resistance gives good results in the plane wave frequency range with moderate Mach-number flow. In this paper, the experiments on the acoustic performance of the POC-X in the non-plane wave frequency range with low Mach-number flow (M = 0.01) are introduced. Starting from the earlier findings, procedure to obtain an estimate for the acoustic performance of the filter in the entire audio frequency range is proposed. Using the computationally effective semi-empirical model presented in this paper is especially reasonable when optimizing the complete exhaust system of an IC-engine for the maximum noise reduction.

  • 68. Hynninen, A.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Procedure to estimate the in-duct sound power in the high frequency range with non-plane waves2012Inngår i: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012: Volume 10, 2012, ASME Press, 2012, s. 8026-8036Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.

  • 69. Hynninen, A.
    et al.
    Åbom, Mats.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Procedure to estimate the in-duct sound power in the high frequency range with non-plane waves2012Inngår i: ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012, ASME Press, 2012, s. 181-191Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.

  • 70.
    Hynninen, Antti
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. VTT Technical Research Centre of Finland Ltd.
    Turunen, R.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. 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. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Acoustic source data for medium speed IC-engines2012Inngår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 134, nr 5, s. 051008-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. The goal of the present study is to numerically and experimentally investigate the medium speed IC-engine acoustic source characteristics, not only in the plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multiload measurements by using a one-dimensional process simulation code. The low frequency in-duct exhaust noise of a medium speed IC-engine can be quite accurately predicted. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods; using the simple cross-spectra averaging method seems promising in this instance.

  • 71.
    Hynninen, Antti
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. VTT Technical Research Centre of Finland Ltd.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic Simulation of Medium Speed IC-Engine Exhaust Gas After Treatment Devices with Substrate2014Annet (Fagfellevurdert)
    Abstract [en]

    The after treatment devices (ATD) used in internal combustion engine (IC-engine) exhaust systems are mainly designed with emphasis on emission control, i.e. chemical efficiency, while paying less attention to the acoustic performance. In automotive applications, the duct diameters are so small that studying the acoustic wave propagation only in the plane wave frequency range is usually sufficient. In the case of medium speed IC-engines, used for example in power plants and ships, the three dimensional acoustic phenomena must also be taken into account. The main elements of the medium speed IC-engine ATD are the selective catalytic reducer (SCR) and oxidation catalyst (OC), which are based on a large amount of coated channels, i.e. the substrates. The number and type of the substrates depends not only on the regional environment legislations but also on the engine type. In this study the acoustic attenuation of a medium speed IC-engine ATD is simulated and the results are compared with measurements. The focus is in the low and mid frequency range. That is, the three dimensional waves inside the ATD are taken into account whereas only the plane waves are assumed to propagate at the inlet and outlet ports. The paper also discusses how to extend the classical one dimensional two-port solution into the higher frequencies. Using the computationally effective two-port solution in a wider frequency range is of great importance, e.g., when searching the acoustically optimal substrate configuration.

  • 72. Hynninen, Antti
    et al.
    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).
    Acoustic Source Characterization for Prediction of Medium Speed Diesel Engine Exhaust Noise2014Inngår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 136, nr 2, s. 021008-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To achieve reliable results when simulating the acoustics of the internal combustion engine (IC-engine) exhaust system and its components, the source characteristics of the engine must be known. In the low frequency range only plane waves propagate and then one-port source data can be determined using, for example, the acoustic multiload method. For the medium speed IC-engines used in power plants and ships, the exhaust duct noise often needs to be analyzed up to 10 kHz, i.e., far beyond the plane wave range, and it is then more appropriate to use acoustic power to characterize the source. This power should ideally be measured under reflection-free conditions in the exhaust duct. The results from an earlier study showed that a suitable way to characterize the source for any frequency is to determine the in-duct sound power by extending the plane wave formulation with frequency band power weighting factors. The aim of this study is to apply this high frequency range method in situ to a real test engine. Another aim is to define, theoretically, how to combine the source data in the low frequency plane wave range with those in the high frequency nonplane wave range using a source sound power formulation.

  • 73. Hynninen, Antti
    et al.
    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).
    Determination of in-duct sound power beyond the plane wave range using wall-mounted microphones2015Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 99, s. 24-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When studying the acoustic wave propagation in a duct, the frequency range can be divided into the low frequency plane wave range and the high frequency range with non-plane waves. In the low frequency range, the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct, the lower the frequency limit of the non-plane waves. Therefore, also taking into account the three-dimensional acoustic wave propagation is important, especially when considering the duct systems used in large machines. In practice often a harsh environment and immobile structures restrict the use of standardized noise measuring methods. For instance to characterize the exhaust noise of medium speed internal combustion engines (IC-engines) in situ, the in-duct sound pressures are measured using wall-mounted microphones. Then the low frequency range source sound power can be estimated by wave decomposition ("two-microphone method"). Often a three-microphone array is used to cover a sufficiently large frequency range. One way to formulate the sound pressure and sound power relationship in the high frequency range is to weight the sound pressures at the duct wall in one-third octave bands. The aim of this study is to extend the classical plane wave formulation by determining these weighting factors, so that a three-microphone array also can be used beyond the plane wave range. The results from numerical approach are compared to experimental data.

  • 74. Hynninen, Antti
    et al.
    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).
    Simulation of the particle oxidation catalyst POC (R) acoustics2014Inngår i: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 62, nr 5, s. 368-374Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reduction of the exhaust noise from internal combustion engine (IC-engine) is mainly managed by proper silencer design, while less attention is paid to the acoustic performance of the after treatment devices (ATD). It is known from the earlier studies, that the transmission loss of a typical ATD unit can be quite significant. An ATD unit for diesel engines is classically assembled from several specific parts such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POC (R)). The POC (R) substrate studied in this paper is of type POC-X, which consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. In this paper acoustic two-port simulation models for POC-X are proposed. First model is built up starting from the classical Kirchhoff solution for prediction of the acoustic wave attenuation in narrow channels. According to experimental studies, correction factors to the narrow channel two-port model are proposed. Second model is derived by treating the filter as a lumped acoustic resistance, dependent on the flow resistivity coefficients obtained from the pressure drop measurements.

  • 75.
    Jansson, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Vilela De Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Karlsson, Mikael
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Adaptive stabilized finite element framework for simulation of vocal fold turbulent fluid-structure interaction2013Inngår i: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, s. 1-9Konferansepaper (Fagfellevurdert)
    Abstract [en]

    As a step toward building a more complete model of voice production mechanics, we assess the feasibility of a fluid-structure simulation of the vocal fold mechanics in the Unicorn incompressible Unified Continuum framework. The Unicorn framework consists of conservation equations for mass and momentum, a phase function selecting solid or fluid constitutive laws, a convection equation for the phase function and moving mesh methods for tracking the interface, and discretization through an adaptive stabilized finite element method. The framework has been validated for turbulent flow for both low and high Reynolds numbers and has the following features: implicit turbulence modeling (turbulent dissipation only occurs through numerical stabilization), goal-oriented mesh adaptivity, strong, implicit fluid-structure coupling and good scaling on massively parallel computers. We have applied the framework for turbulent fluid-structure interaction simulation of vocal folds, and present initial results. Acoustic quantities have been extracted from the framework in the setting of an investigation of a configuration approximating an exhaust system with turbulent flow around a flexible triangular steel plate in a circular duct. We present some results of the investigation as well as results of the framework applied to other problems.

  • 76.
    Jiang, Yan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Acoustic Modeling of Heat Exchangers2008Inngår i: 37th International Congress and Exposition on Noise Control Engineering (inter-noise 2008), Shanghai, China. 26-29 October 2008, 2008Konferansepaper (Fagfellevurdert)
  • 77.
    Jiang, Yan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Feng, Leping
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Timouchev, S
    Maliczak, C
    Investigation of sound generation from an axial fan for engine cooling2007Inngår i:  , 2007Konferansepaper (Fagfellevurdert)
  • 78.
    Jiang, Yan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Frid, A.
    Fehse, K.R.
    Cooling Fan Noise Control in Railway VehiclesManuskript (preprint) (Annet vitenskapelig)
  • 79.
    Jiang, Yan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Timouchev, S.
    Investigation of Sound Generation from an Axial Fan for Engine coolingManuskript (preprint) (Annet vitenskapelig)
  • 80. Johansson, C. -G
    et al.
    Saine, K.
    Johansson, P.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Exhaust noise - A new novel in-situ measurement technology in duct2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 1639-1648Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The noise emission from large internal combustion engines, from 500 kW to 20 MW, is inherently difficult to predict with a high degree of confidence. How the actual noise field propagates within a complex exhaust gas system and how to measure exhaust noise where the gas flow in the duct could be as high as 40 m/s and temperature about 350 degree. This translates to increased cost for silencer over-sizing or added costs associated with an exhaust gas system that fails to meet the required noise signature. This paper deals with a new and verified hot gas (< 600 C) in-situ noise measurement technology called SESaM. It makes it possible to accurately measure source strength and specific insertion loss of the various components in the exhaust train behind large 2 or 4 stroke diesels and power plant gas turbine, also under field conditions. When designing an exhaust system for diesel engine it is most important to have a correct source spectrum for the engine and the noise requirement raised by the final customer in order to do the precision design for the attenuation in the system. In the past the source spectrum of diesel engines always has been an issue of large uncertainty due to the fact that no general reliable measurement procedure exists. The paper presents the practical induct SESaM technology and discusses measurement results versus the time consuming and less accurate classic method.

  • 81.
    Kabral, Raimo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Du, Lin
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Vibrationsövervakning.
    Optimum Sound Attenuation in Flow Ducts Based on the "Exact" Cremer Impedance2016Inngår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 102, nr 5, s. 851-860Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Cremer impedance (Acustica 3, 1953) [1] is the locally reacting boundary condition that maximizes the attenuation of a certain mode in a uniform wave guide taken as the lowest order mode or "plane" wave. This paper presents the analysis of the "exact" Cremer impedance model, i.e., the high frequency asymptotic results proposed by Tester for uniform mean flow (JSV 28(2), 1973) [2] are extended to lower frequencies. It is shown that significantly larger attenuation per unit length can be obtained using the exact instead of the asymptotic solution. However, for sufficiently low frequencies the "exact" Cremer solution and optimum attenuation is requiring a wall impedance with a negative real part, i.e. an active boundary. In addition, the effect of a finite length on the resulting attenuation is studied using a finite element method for solving the convected wave equation. Finally, it is demonstrated how a silencer can be built that realize the optimum Cremer impedance at a given frequency by using a micro-perforated panel and locally reacting cavities. The performance of the optimized silencer is determined experimentally and the results are compared to the prediction of the finite element model.

  • 82.
    Kabral, Raimo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Du, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Knutsson, M
    A compact silencer for the control of compressor noise2014Inngår i: SAE International Journal of Engines, ISSN 1946-3936, Vol. 7, nr 3, s. 1572-1578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current trends for IC-engines are driving the development of more efficient engines with higher specific power. This is true for both light and heavy duty vehicles and has led to an increased use of super-charging. The super-charging can be both in the form of a single or multi-stage turbo-charger driven by exhaust gases, or via a directly driven compressor. In both cases a possible noise problem can be a strong Blade Passing Frequency (BPF) typically in the kHz range and above the plane wave range. In this paper a novel type of compact dissipative silencer developed especially to handle this type of problem is described and optimized. The silencer is based on a combination of a micro-perforated (MPP) tube backed by a locally reacting cavity. The combined impedance of micro-perforate and cavity is chosen to match the theoretical optimum known as the Cremer impedance at the mid-frequency in the frequency range of interest. Due to the high damping achieved at the Cremer optimum (hundreds of dB/m) it is easy to create a compact silencer with a significant damping (say > 30 dB) in a range larger than an octave. Both simulations and experimental tests of the novel silencer are presented based on a light duty vehicle application.

  • 83.
    Kabral, Raimo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Du, Lin
    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. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Optimization of Compact Non-Fibrous Silencer for the Control of Compressor Noise2016Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2016-June, nr JuneArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The concept of IC engine downsizing is a well-adapted industry standard, enabling better fuel conversion efficiency and the reduction of tailpipe emissions. This is achieved by utilizing different type of superchargers. As a consequence, the additional charger noise emission, at the IC engine inlet, can become a problem. In order to address such problem, the authors of this work have recently proposed a novel dissipative silencer for effective and robust noise control of the compressor. Essentially, it realizes an optimal flow channel impedance, referred to as the Cremer impedance. This is achieved by means of a straight flow channel with a locally reacting wall consisting of air cavities covered by an acoustic resistance, e.g., a micro-perforated panel (MPP). In this paper, an improved optimization method of this silencer is presented. The classical Cremer impedance model is modified to account for mean flow dependence of the optimal wave number. This modified model leads to significantly different impedance values compared to the classical model and consequently, the high damping of the classical model (hundreds of dB/m) is further increased. Moreover, the modeling herein, is performed by solving the convective wave equation, vital for accounting mean flow effects. The presented model is finally validated by experimental results included in the paper.

  • 84.
    Kabral, Raimo
    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).
    El Nemr, Yasser
    Ludwig, Carlos
    Mirlach, Robert
    Koutsovasilis, Panagiotis
    Masrane, A
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Experimental acoustic characterization of automotive twin-scroll turbine2017Inngår i: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017, KTH Royal Institute of Technology, 2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The present paper focuses on the experimental determination of automotive twin-scroll turbine acoustic performance. The unique test-rig for automotive turbocharger acoustics at KTH CCGEx laboratory is further developed to enable testing of modern twin-scroll turbines under controlled laboratory conditions. It is shown how the passive acoustic properties of such turbines can be accurately characterized by means of an acoustic three-port formulation. Governing equations along with the new test-rig design are presented and discussed in detail. Furthermore, complementary results from the first experimental determination of twin-scroll turbine acoustic three-port data are presented.

  • 85.
    Kabral, Raimo
    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).
    Rammal, H.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustical methods for investigating turbocharger flow instabilities2013Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 4, s. 2013-01-1879-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to increase the internal combustion engine efficiency turbocharging is today widely used. The trend, in modern engine technology, is towards higher boost pressures while keeping the combustion pressure raise relatively small. The turbocharger surge occurs if the pressure at the outlet of the compressor is greater than it can maintain, i.e., a reverse flow will be induced. In presence of such flow conditions instabilities will occur which can couple to incident acoustic (pressure) waves and amplify them. The main objective of the present work is to propose a novel method for investigation of turbocharger flow instabilities or surge precursors. The method is based on the determination of the acoustic two-port data. The active part of this data describes the sound generation and the passive part the scattering of sound. The scattering data will contain information about flow-acoustic interaction and amplification of sound that could occur close to surge. Here the existence of such amplification will be investigated for a compressor operating at different operating points including points near the surge line. In addition the generated sound for reflection-free conditions is also investigated on both the up- and downstream side. All the measurements have been carried out in the unique CCGEx test rig for two-port testing of turbo-compressors.

  • 86.
    Kabral, Raimo
    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).
    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).
    Investigation of flow-acoustic interaction in automotive turbocharger2014Inngår i: Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics, KU Leuven , 2014, s. 1327-1331Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In IC engine design, the surge condition of a turbocharger is a well-recognized phenomena. As the resulting global fluctuation of mass flux in the intake system is hazardous, the implemented safety margins are large. In order to, reduce such safety margins and employ turbochargers more efficiently, it is of interest to investigate acoustic fields as a possible surge triggering mechanism. Regardless the increasing relevance of this topic today, only few publications exist addressing the acoustics of turbochargers from the perspective of surge prediction and triggering. In the present paper acoustical properties of an automotive turbocharger are experimentally studied at the limit of stable operation as well as under normal operating conditions in the unique CCGEx test rig at KTH. The full two-port data including passive and active parts is determined and utilized to investigate the possible coupling effects between unstable flow and acoustic fields. The local flow instabilities, occurring at the limit of globally stable operation, can interact with the acoustic field and amplify incident sound waves which eventually can lead to an unstable situation and surge. This effect can be studied from the passive two-port data. In addition the active data can be used to find the occurrence of compact correlated sources in the compressor such as rotating stall a pre-cursor of surge.

  • 87.
    Kabral, Raimo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Investigation of turbocharger compressor surge inception by means of an acoustic two-port modelInngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet vitenskapelig)
  • 88.
    Kabral, Raimo
    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).
    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).
    Investigation of turbocharger compressor surge inception by means of an acoustic two-port model2018Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 412, s. 270-286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of centrifugal compressors have increased tremendously in the last decade being implemented in the modern IC engine design as a key component. However, an efficient implementation is restricted by the compression system surge phenomenon. The focus in the investigation of surge inception have mainly been on the aerodynamic field while neglecting the acoustic field. In the present work a new method based on the full acoustic 2-port model is proposed for investigation of centrifugal compressor stall and surge inception. Essentially, the compressor is acoustically decoupled from the compression system, hence enabling the determination of sound generation and the quantification of internal aero-acoustic coupling effects, both independently of the connected pipe system. These frequency dependent quantities are indicating if the compressor is prone to self-sustained oscillations in case of positive feedback when installed in a system. The method is demonstrated on experimentally determined 2-port data of an automotive turbocharger centrifugal compressor under a variety of realistic operating conditions.

  • 89. Karlsson, M.
    et al.
    Knutsson, M.
    Åbom, Mats
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Predicting Fluid Driven Whistles in Automotive Intake and Exhaust Systems2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work explores how fluid driven whistles in complex automotive intake and exhaust systems can be predicted using computationally affordable tools. Whistles associated with unsteady shear layers (created over for example side branches or perforates in resonators) are studied using vortex sound theory; vorticity in the shear layer interacts with the acoustic field while being convected across the orifice. If the travel time of a hydrodynamic disturbance over the orifice reasonably matches a multiple of the acoustic period of an acoustic feedback system, energy is transferred from the flow field to the acoustic field resulting in a whistle. The actual amplitude of the whistle is set by non-linear saturation phenomena and cannot be predicted here, but the frequency and relative strength can be found. For this not only the mean flow and acoustic fields needs to be characterized separately, but also the interaction of the two. The flow field is studied using steady state CFD simulations while the acoustic field is calculated with a standard linear acoustics solver. Already from this information one could derive design charts. But to pin point the whistle the interaction of the two fields is needed. This can be achieved numerically or experimentally. In this case available experimental data from other geometries have been rescaled for use in the present case. Finally, linear stability theory is applied to the complete system. Using the proposed method the whistling frequency of a complex intake prototype system was predicted very accurately.

  • 90.
    Karlsson, M.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Glav, Ragnar
    Aeroacoustics of duct branches: with application to silencers2011Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The inclusion of flow-acoustic interaction effects in linear acoustic multiport models has been studied. It is shown, using a T-junction as illustration example, that as long the acoustic system is linear the required information is included in a scattering matrix obtained by experimental or numerical studies. Assuming small Mach numbers and low frequencies-as in most automotive silencer applications-the scattering matrix for the T-junction can be approximated using quasi-steady models. Models are derived that holds for all possible configurations of grazing and bias flow in the T-junctions. The derived models are then used to predict the performance of a novel silencer concept, where a resonator is formed by acoustically short-circuiting the inlet and outlet ducts of a flow reversal chamber. The agreement between experiments and simulations is excellent, justifying the use of the quasi-steady modeling approach.

  • 91.
    Karlsson, Mikael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Glav, Ragnar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The Herschel-Quincke tube: The attenuation conditions and their sensitivity to mean flow2008Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 124, nr 2, s. 723-732Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The classic Herschel-Quincke tube is a parallel connection of two ducts yielding multiple noise attenuation maxima via destructive interference. This problem has been discussed to different degrees by a number of authors over the years. This study returns to the basics of the system for the purpose of furthering the understanding of the conditions necessary for noise attenuation and especially their sensitivity to mean flow. First, the transmission loss for an N-duct system with mean flow and arbitrary conditions of state in the different ducts is derived. Next, the two types of conditions yielding the attenuation maxima are studied. In addition to a discussion of the underlying physics, generic expressions for frequencies at which maximum attenuation occur are presented. Experiments without mean flow generally show good agreement with theory based on straight duct elements. However, more detailed models may be required for accurate simulations in the presence of mean flow. A simple model compensating for the losses associated with bends is shown to improve the results significantly for the geometry studied.

  • 92.
    Karlsson, Mikael
    et al.
    Swenox AB.
    Holmberg, Andreas
    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.
    Fallenius, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fransson, Jens
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Experimental determination of the aero-acoustic properties of an in-duct flexible plate2008Inngår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The potential reduction of the aeroacoustic noise generated by an in duct plate, byallowing it to be flexible, is studied experimentally. The test object is a triangular plateinserted at an angle in a circular flow duct. Results are given for the active and passiveacoustic properties. In addition the flow field and the vibrations of the plate arecharacterized. It is found that an appropriately yielding plate reduces the flow generatednoise while keeping the mean flow field unaffected.

  • 93.
    Karlsson, Mikael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Aeroacoustics of T-junctions: An experimental investigation2010Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 329, nr 10, s. 1793-1808Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An experimental method for determining the aeroacoustic properties of side branch orifices allowing for any combination of grazing and bias flow is presented. The geometry studied, a T-junction, is treated as an active acoustic three-port. The passive properties, describing the reflection and transmission of an incident acoustic wave, are described by a system matrix while the active properties are described by a source vector. Expressions for the acoustic impedance under various mean flow and acoustic incidence configurations are developed. In addition, methods for identifying regions where the system can generate sound, by studying only the passive properties, are discussed. A self-sustained oscillation is triggered at one of the identified regions by coupling a resonant system to the three-port.

  • 94.
    Karlsson, Mikael
    et al.
    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.
    Linear stability analysis applied to flow duct acoustics2010Inngår i: 20th International Congress on Acoustics 2010, ICA 2010 - Incorporating Proceedings of the 2010 Annual Conference of the Australian Acoustical Society: Volume 1, 2010, s. 182-185Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Linear stability analysis is applied to configurations based on a T-junction subjected to grazing flow. This setup is a well-known case where flow-acoustic interaction can result in aperture tones provided sufficient acoustic feedback is present. The flow acoustic interaction is characterised as Rayleigh impedances, these together with the acoustic impedance of the attached components result in a total impedance that characterises the system. Stability analysis is then applied to the derived total impedance using a slightly modified version of the Nyquist criterion as known from control theory.

  • 95.
    Karlsson, Mikael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On the Use of Linear Acoustic Multiports to Predict Whistling in Confined Flows2011Inngår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, nr 1, s. 24-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of linear acoustic multiport models to analyse the existence of flow driven instabilities, that is - self-sustained oscillators or whistles - is addressed. By combining the scattering and reflection matrices for a system and searching for eigenfrequencies (zeros) in the critical half-plane, the existence of exponentially growing instabilities can be determined. In practice, the available frequency domain data are only known along the real axis; then the search for zeros may be done via the so-called Nyquist stability criterion generalized to an N-degree of freedom system. The method has been validated by two test cases, a T-junction and a Herschel-Quincke tube. In both cases, the occurrence and the frequencies of the self-sustained oscillations were correctly predicted.

  • 96.
    Karlsson, Mikael
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Quasisteady model of the acoustic scattering of a T- Junction2011Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 21, s. 5131-5137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    T-junctions are common elements in flow duct networks. It is shown that for low Strouhal numbers, based on the duct diameter, their acoustic scattering properties can be described using an incompressible quasi-steady model. Models are derived for systems subjected to combinations of grazing and bias mean flow, and are shown to work in both the limiting cases that is, grazing or bias flow alone as well as for the joining or dividing flow configurations. The upper Strouhal number for which the quasi-steady models are applicable is limited by flow-acoustic interaction effects, which differ significantly between the different flow configurations. Generally the models are applicable up to Strouhal numbers of approximately 0.1-0.2, which is comparable with previous published models for other configurations such as bends and orifices. This range is sufficient to make the model useful in many important engineering applications.

  • 97.
    Karlsson, Mikael
    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).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Lalit, Manan
    Glav, Ragnar
    A Note on the Applicability of Thermo-Acoustic Engines for Automotive Waste Heat Recovery2016Inngår i: SAE International Journal of Materials & Manufacturing, ISSN 1946-3979, E-ISSN 1946-3987, Vol. 9, nr 2, s. 286-293Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A thermo-acoustic engine is a device converting thermal energy into high amplitude acoustic waves that can be harvested, for example, to obtain electricity. The core of the device is a stack/regenerator along which a temperature gradient is created using one hot and one cold heat exchanger. Correctly designed, the thermal interaction between the working fluid and the regenerator assists in amplifying incident acoustic waves. Previous studies have indicated good efficiency obtained with a system of low geometrical complexity. However, for the practical application of this technique it is vital to understand and identify critical design parameters and operating conditions. This is of special interest in automotive applications where the operating conditions vary significantly over a drive cycle. This works aims at providing a framework for studying the net power generation over a drive cycle. First, an engineering non-linear model for the efficiency of the thermo-acoustic engine is established. It is based on low-order acoustic networks that have the advantage of being computationally effective and allows for individual optimization of components. This model is then used to loop over a drive cycle of a typical commercial vehicle, while also accounting for pump losses given by the heat exchange processes. Although an engine not optimized for the present problem was used, promising performance, with a thermal efficiency of 7%, was found. Also the importance of adapting the engine to the varying operating conditions over the drive cycle was illustrated.

  • 98.
    Kerres, Bertrand
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.). Competence Center for Gas Exchange.
    Kabral, Raimo
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Competence Center for Gas Exchange.
    Nair, Vineeth
    Department of Aerospace Engineering, Indian Institute of Technology, Madras.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Competence Center for Gas Exchange.
    The Hurst exponent as a model-free precursor of centrifugal compressor surgeManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We investigate the generalized Hurst exponent, a measure of signal fractality, as an indicator of compression system stability. Tests were run on a centrifugal compressor of a light duty turbocharger on two test rigs: an acoustic test rig and a cold gas stand. While the compressor type is the same on both test benches, the other components of the compression system differ significantly, including the Greitzer B value and the presence of silencers. The Hurst exponent can be used to distinguish between stable and near-surge operation of the compressor independent of the compression system, with values larger than 0.5 at stable operation and values below 0.2 at the surge line. By extending the analysis towards a general Hurst exponent, we can identify a precursor to compressor surge that is also valid for both systems, namely the switch from monofractality to multifractality of the compressor outlet pressure signal. At low compressor speeds, this switch occurs at on the negative slope section of the compressor characteristic, where the system is theoretically fully stable. At higher compressor speeds, it coincides with the switch from negative to zero-slope, where theoretical models also predict compression system instability.

  • 99.
    Kierkegaard, Axel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Allam, Sabry
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Simulations of whistling and the whistling potentiality of an in-duct orifice with linear aeroacoustics2012Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, nr 5, s. 1084-1096Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 100.
    Kierkegaard, Axel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Simulations of the Whistling Potentiality of an In-Duct Orifice with Linear Aeroacoustics2010Inngår i: 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010, 2010Konferansepaper (Annet vitenskapelig)
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