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  • 101.
    Kierkegaard, Axel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Heopffner, Jerome
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Åkervik, Espen
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Identifications of sources of sound in low Mach number flows by the use of flow field eigenmodes2006Inngår i: 13th International Congress on Sound and Vibration 2006, 2006, s. 2967-2974Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a method to study sound generation processes in low Mach Number flows. Instead of the full flow field obtained from e.g a DNS, we consider a base flow together with a time-dependent perturbation ,where the perturbation satisfy the Navier-Stokes equations linearized around the base-flow. In a reduced model the perturbation is approximated by a linear combination of the cigenmodes of a corresponding eigenvalue problem. The behavior in time is determined by the corresponding eigenvalues. Curie's equation is used to calculate the acoustic field. By studying the source terms in Curie's equation, it is possible to identify mechanisms for sources of sound. This makes it possible to study how the different sources of sound depend on different structures of the flow field. We apply the methodology on a two- dimensional flow over a cavity with smoothed corners. Results of acoustic pressure in the far field and source strengths for different superpositions of eigenmodes are presented.

  • 102.
    Kierkegaard, Axel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    FREQUENCY-DOMAIN LINEARIZED NAVIER-STOKES EQUATIONS FOR FLOWDUCT COMPUTATIONAL AEROACOUSTICS2012Konferansepaper (Annet vitenskapelig)
  • 103. Kim, D. -Y
    et al.
    Ih, J. -G
    Zhang, Zhe
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A virtual herschel-quincke tube using slow sound2017Inngår i: INTER-NOISE 2017 - 46th International Congress and Exposition on Noise Control Engineering: Taming Noise and Moving Quiet, Institute of Noise Control Engineering , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    While an acoustic wave propagates along a duct, of which the wall is treated with either dissipative or a reactive material, the phase speed can be slowed down because of wave dispersion. It has been thought that such slow sound can be used for a novel control method to reduce the in-duct noise at low to medium frequencies generated from a fluid machinery system. In this work, the Herschel-Quincke tube (hereafter, H-Q tube), which exploits the path length difference of two parallel ducts, is modified to demonstrate the application potential of the slow sound. A test rig is designed to create the two different phase speeds by arranging the two parallel, equal-length ducts inside a main duct, one of them is hard-walled and the other one lined with a periodic array of resonators. This slow sound H-Q device is then modelled by both analytical and numerical methods assuming a plane wave incidence. Also, an experiment is conducted to measure the transmission loss. The result reveals a low frequency peak (TL-30 dB) in the range of 200-400 Hz, which occurs far below the lowest resonance of the resonator. At the original resonance frequency of 691 Hz, a small attenuation (TL~6 dB) is obtained due to the fact that one duct is subject to a high loss, and the other is without appreciable loss. The result clearly demonstrates the potential of applying slow sound device to overcome the spatial limitation of the classical H-Q tube.

  • 104.
    Kim, Da-Young
    et al.
    Ctr Noise & Vib Control, Korea Adv Inst Sci & Technol, Dept Mech Eng, Daejeon 34141, South Korea..
    Ih, Jeong-Guon
    Ctr Noise & Vib Control, Korea Adv Inst Sci & Technol, Dept Mech Eng, Daejeon 34141, South Korea..
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Virtual Herschel-Quincke tube using the multiple small resonators and acoustic metamaterials2020Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 466, artikkel-id UNSP 115045Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study is on the practical application of the acoustic metamaterials to the design of a silencer with high acoustic and geometric efficiencies, and negligible pressure drop. The object is to achieve broadband and low-frequency attenuation simultaneously by combining the effects of resonance, periodicity, phase difference, and impedance mismatch. An array of multiple small resonators, which is periodically applied to the wall of a duct, invokes the dispersion of sound propagating in the duct. This phenomenon is implemented to construct a virtual Herschel-Quincke (HQ) tube system. The main duct is split into two parallel ducts of the same length: a rigid duct and a duct with a wall covered by the periodic resonators. For a modelling of sound propagation in a dispersive duct, the phase speed of sound is analytically derived in the presence of a mean flow. Also, the attenuation conditions of the virtual HQ tube are proposed to establish a guideline in selecting the proper design parameters for achieving the required transmission loss (TL) in the desired frequency range. The predicted TL spectra are compared with the test results, for a virtual HQ tube system with 9 identical quarter-wavelength tube resonators, and they generally agree well. With increasing flow speed, the amount of attenuation decreases a bit, but the general spectral characteristics are maintained for vertical bar M vertical bar <= 0.1. Based on the same principle, the acoustic metamaterials (AMM) are applied to the practical silencer design to achieve the wide-band sound reduction at low- to mid-frequencies for a given small space. A virtual HQ tube having 26 cells of AMM is tested, of which a cell is composed of 3 types of quarter-wavelength tube resonators. The experiment well validates the predicted TL. The results show that TL is at least 5 dB for a wide frequency range of 230-1000 Hz. The additional volume due to the attachment of the AMM layer is only 40%, while the TL is far larger than that of the simple expansion chamber or the dissipative silencer having the same excess volume.

  • 105. Knutsson, M.
    et al.
    Lennblad, J.
    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.
    A study on acoustical time-domain two-ports based on digital filters with application to automotive air intake systems2011Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analysis of pressure pulsations in ducts is an active research field within the automotive industry. The fluid dynamics and the wave-transmission properties of internal combustion (IC) engine intake and exhaust systems contribute to the energy efficiency of the engines and are hence important for the final amount of CO2 that is emitted from the vehicles. Sound waves, originating from the pressure pulses caused by the in- and outflow at the engine valves, are transmitted through the intake and exhaust system and are an important cause of noise pollution from road traffic at low speeds. Reliable prediction methods are of major importance to enable effective optimization of gas exchange systems. The use of nonlinear one-dimensional (1D) gas dynamics simulation software packages is widespread within the automotive industry. These time-domain codes are mainly used to predict engine performance parameters such as output torque and power but can also give estimates of radiated orifice noise. However, components with large cross-dimensions, fluid-structural interaction, frequency-dependent damping and boundary conditions are difficult to describe analytically in 1D in the time domain. Since a frequency-domain description in the form of a two-port is normally straightforward to obtain analytically, numerically or experimentally it is of interest to introduce these in time-domain calculations as black box models. This paper suggests the use of Finite Impulse Response (FIR) filters as a method to achieve this improvement. An initial study is presented where tabulated frequency-domain two-port data representing an air cleaner unit on the impedance form is inversely transformed to the time domain and used as FIR filters in nonlinear time-domain 1D calculations with good accuracy. Favourable attenuation, achieved from the filter paper itself, is demonstrated experimentally as well as by the calculations. 

  • 106. Knutsson, M.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Acoustic analysis of charge air coolers2007Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the results from a study of the acoustic properties of charge air coolers for passenger cars. Charge air coolers are used on turbo charged engines to increase the overall performance. The cooling of the charged air results in higher density and thus volumetric efficiency. Important for petrol engines is also that the knock margin increases with reduced charge air temperature. A property that is still not very well investigated is the sound transmission through charge air coolers. The pressure drop in the narrow cooling tubes results in frequency dependent resistive effects on the transmitted sound that is non negligible. Since the cross dimensions of the connecting tanks, located on each side of the cooling tubes, are big compared to the wave length for engine breathing noise, three dimensional effects can also be of importance. In this study an acoustic two-port for sound propagation in narrow tubes, including the effect of viscous and thermal boundary layers, is combined with three dimensional acoustic finite element modeling to represent a complete air-to-air charge air cooler. From this a linear frequency domain model for the entire charge air cooler is extracted in the form of a two-port. The frequency dependent transmission loss is calculated and compared with corresponding experimental data. Finally, there is a discussion of the results and on how the acoustic response of charge air coolers could be modified.

  • 107. Knutsson, M.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Sound propagation in narrow channels with arbitrary cross sections and superimposed mean flow with application to charge air coolers2007Inngår i: 14th International Congress on Sound and Vibration 2007, ICSV 2007, 2007, s. 2633-2640Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Charge air coolers are used on turbo charged IC-engines to enhance the overall gas exchange performance. The cooling of the charged air results in higher density and thus volumetric efficiency. Important for petrol engines is also that the knock margin increases with reduced charge air temperature. A property that is still not very well investigated is the sound transmission through a charge air cooler. The pressure drop in the narrow cooling tubes results in frequency dependent resistive effects on the transmitted sound that is non negligible. As the cross sections of the cooling tubes are neither circular nor rectangular, no analytical solution accounting for a superimposed mean flow exists. The cross dimensions of the connecting tanks, located on each side of the cooling tubes, are large compared to the wavelength for engine breathing noise, here including frequencies up 1.5 kHz, so three dimensional effects are important. In this study an acoustic two-port for sound propagation in narrow tubes, including the effect of viscous and thermal boundary layers, is calculated utilizing a 2D finite element solution scheme. Analytical solutions for circular cross sections are additionally calculated for comparison. The two-port is thereafter combined with 3D acoustic finite element modelling to represent the transmission properties of the charged air when passing the complete air-to-air charge air cooler. From this a linear frequency domain model for the entire charge air cooler is extracted in the form of a two-port. The frequency dependent transmission loss is calculated and compared with corresponding experimental data. Finally, there is a discussion of the results and the potential of using charge air coolers to control the acoustic response of intake systems.

  • 108.
    Knutsson, Magnus
    et al.
    Volvo Car Corporation, Sweden.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Volvo Car Corporation, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. Volvo Car Corporation, Sweden.
    Lennblad, J
    Volvo Car Corporation, Sweden.
    A study on acoustical time-domain two-ports based on digital filters with application to automotive air intake systems2011Inngår i: SAE International Journal of Passenger Cars - Mechanical Systems, ISSN 1946-3995, Vol. 4, nr 2, s. 970-982Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analysis of pressure pulsations in ducts is an active research field within the automotive industry. The fluid dynamics and the wave-transmission properties of internal combustion (IC) engine intake and exhaust systems contribute to the energy efficiency of the engines and are hence important for the final amount of CO 2 that is emitted from the vehicles. Sound waves, originating from the pressure pulses caused by the in- and outflow at the engine valves, are transmitted through the intake and exhaust system and are an important cause of noise pollution from road traffic at low speeds. Reliable prediction methods are of major importance to enable effective optimization of gas exchange systems. The use of nonlinear one-dimensional (1D) gas dynamics simulation software packages is widespread within the automotive industry. These time-domain codes are mainly used to predict engine performance parameters such as output torque and power but can also give estimates of radiated orifice noise. However, components with large cross-dimensions, fluid-structural interaction, frequency-dependent damping and boundary conditions are difficult to describe analytically in 1D in the time domain. Since a frequency-domain description in the form of a two-port is normally straightforward to obtain analytically, numerically or experimentally it is of interest to introduce these in time-domain calculations as black box models. This paper suggests the use of Finite Impulse Response (FIR) filters as a method to achieve this improvement. An initial study is presented where tabulated frequency-domain two-port data representing an air cleaner unit on the impedance form is inversely transformed to the time domain and used as FIR filters in nonlinear time-domain 1D calculations with good accuracy. Favourable attenuation, achieved from the filter paper itself, is demonstrated experimentally as well as by the calculations.

  • 109.
    Knutsson, Magnus
    et al.
    Volvo Car Corporation.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Low frequency damping from turbulence with application to charge air coolers2012Inngår i: Int. Congr. Expos. Noise Control Eng., INTER-NOISE, 2012, s. 9424-9433Konferansepaper (Fagfellevurdert)
    Abstract [en]

    As a consequence of its contribution to the global warming the necessity of reducing the CO2 emissions from transportation is dramatically increasing. One effective measure to meet this requirement with respect to the passenger car segment is to conduct IC-engine downsizing. To meet requirements for high power and torque output turbo- or supercharging in combination with charge air cooling is regularly used. Both compressors and charge air coolers will largely influence the sound transmission though the air intake system. In order to make a proper system optimization where pressure drop, heat exchange efficiency and acoustics are balanced within a given space accurate models are required. Inside most charge air coolers the cooling takes place in parallel narrow channels where boundary layers dominate the behavior. This paper presents a new acoustic model for charge air coolers where low frequency damping from interaction between acoustic boundary layers and turbulence is important. The predictions are compared with experimental data taken at room temperature and show good agreement. More than 5 dB transmission loss is demonstrated at low frequencies that can be used for noise control.

  • 110.
    Knutsson, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO.
    Sound propagation in narrow tubes including effects of viscothermal and turbulent damping with application to charge air coolers2009Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 320, s. 289-321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Charge air coolers (CACs) are used on turbocharged internal combustion engines to enhance the overall gas-exchange performance. The cooling of the charged air results in higher density and thus volumetric efficiency. It is also important for petrol engines that the knock margin increases with reduced charge air temperature. A property that is still not very well investigated is the sound transmission through a CAC. The losses, due to viscous and thermal boundary layers as well as turbulence, in the narrow cooling tubes result in frequency dependent attenuation of the transmitted sound that is significant and dependent on the flow conditions. Normally, the cross-sections of the cooling tubes are neither circular nor rectangular, which is why no analytical solution accounting for a superimposed mean flow exists. The cross-dimensions of the connecting tanks, located on each side of the cooling tubes, are large compared to the diameters of the inlet and outlet ducts. Three-dimensional effects will therefore be important at frequencies significantly lower than the cut-on frequencies of the inlet/outlet ducts. In this study the two-dimensional finite element solution scheme for sound propagation in narrow tubes, including the effect of viscous and thermal boundary layers, originally derived by Astley and Cummings [Wave propagation in catalytic converters: Formulation of the problem and finite element scheme, Journal of Sound and Vibration 188 (5) (1995) 635-657] is used to extract two-ports to represent the cooling tubes. The approximate solutions for sound propagation, accounting for viscothermal and turbulent boundary layers derived by Dokumaci [Sound transmission in narrow pipes with superimposed uniform mean flow and acoustic modelling of automobile catalytic converters, Journal of Sound and Vibration 182 (5) (1995) 799-808] and Howe [The damping of sound by wall turbulent shear layers, Journal of the Acoustical Society of America 98 (3) (1995) 1723-1730], are additionally calculated for corresponding circular cross-sections for comparison and discussion. The two-ports are thereafter combined with numerically obtained multi-ports, representing the connecting tanks, in order to obtain the transmission properties for the charged air when passing the complete CAC. An attractive formalism for representation of the multi-ports based on the admittance relationship between the ports is presented. From this the first linear frequency domain model for CACs, which includes a complete treatment of losses in the cooling tubes and 3D effects in the connecting tanks is extracted in the form of a two-port. The frequency dependent transmission loss is calculated and compared to the corresponding experimental data with good agreement.

  • 111.
    Knutsson, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO.
    The effect of turbulence damping on acoustic wave propagation in tubes2010Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 329, nr 22, s. 4719-4739Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 112.
    Kårekull, Oscar
    et al.
    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.
    CHALLENGES AND OPPORTUNITIES FOR FLOW NOISE PREDICTION IN HVAC SYSTEMS2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the possibilities of noise prediction in Heating Ventilation and Air Conditioning (HVAC) systems using semi empirical scaling laws. An approach is presented where the general noise reference spectra are combined with Reynolds Average Navier Stokes (RANS) simulations. Focus is at applying the suggested noise prediction approach to common HVAC components but also to discuss the properties of the prediction model, e.g. radiation characteristics and chosen reference spectra. A model is presented, using a momentum flux assumption of the noise sources, which is validated by a range of HVAC components of both high and low pressure loss.

  • 113.
    Kårekull, Oscar
    et al.
    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.
    Prediction model of flow duct constriction noise2014Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 82, s. 45-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The scaling law for aerodynamic dipole type of sound from constrictions in low speed flow ducts by Nelson and Morfey is revisited. A summary of earlier published results using this scaling law is presented together with some new data. Based on this, an effort to find a general scaling law for the sound power for components with both distinct and non-distinct flow separation points are made. Special care is taken to apply the same scaling to all data based on the pressure drop. Results from both rectangular and circular ducts, duct flow velocities from 2 to 120 m/s and sound power measurements made both in ducts and in reverberation chambers are presented. The computed sound power represents the downstream source output in a reflection free duct. In particular for the low frequency plane wave range strong reflections from e.g. openings can affect the sound power output. This is handled by reformulating the Nelson and Morfey model in the form of an active acoustic 2-port. The pressure loss information needed for the semi-empirical scaling law can be gained from CFD simulations. A method using Reynold Average Navier Stokes (RANS) simulations is presented, where the required mesh quality is evaluated and estimation of the dipole source strength via the use of the pressure drop is compared to using the turbulent kinetic energy.

  • 114.
    Kårekull, Oscar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Fläkt Woods, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Revisiting the Nelson-Morfey scaling law for flow noise from duct constrictions2015Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 357, s. 233-244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The semi empirical scaling law by Nelson and Morfey [1] predicts the noise generation from constrictions in ducts with low Mach number flows. The results presented here demonstrate that the original model loose accuracy for constrictions of high pressure loss. An extension based on a momentum flux assumption of the dipole forces is suggested and is evaluated against measurement results for orifice geometries of higher pressure loss than earlier evaluated. A prediction model including constrictions at flow duct terminations is also suggested. Improved accuracy for the predictions of the new model are found for orifice geometries of both high and low pressure loss inside and at end of ducts. The extended model is finally evaluated by measurementson a regular ventilation air terminal device.

  • 115.
    Lalit, Manan
    et al.
    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. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    AN ENGINEERING NON-LINEAR MODEL FOR THERMO-ACOUSTIC ENGINES2015Inngår i: PROCEEDINGS OF THE 22ND INTERNATIONAL CONGRESS ON SOUND AND VIBRATION: MAJOR CHALLENGES IN ACOUSTICS, NOISE AND VIBRATION RESEARCH, 2015 / [ed] Crocker, MJ Pawelczyk, M Pedrielli, F Carletti, E Luzzi, S, INT INST ACOUSTICS & VIBRATION , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A thermoacoustic engine is a device converting thermal energy into high amplitude acoustic waves that can be harvested, for example, to electricity. For the practical application of this technique it is vital to identify optimum design parameters and operating conditions. There are numerous reports and tools based on the application of the well-established linear theory first derived by Rott. This is useful for determining the working frequency and yields a first indication of the amplification potential of a given design, but cannot predict the saturation amplitude that is limited by non-linear loss mechanisms. In this work an engineering approach for estimating the final output power of a device is discussed. It is assumed that the fundamental mode of the device is dominating, neglecting the loss of acoustic energy into the harmonics. The core of the engine (heat exchangers and stack/regenerator) is represented as an amplitude-dependent acoustic two port in the frequency domain. To close the system the duct network and acoustic load are treated similarly as the core; all parts are then connected to form a low-order acoustic network. One major difficulty is to represent the non-linear losses in the duct network. Here they are lumped and matched to available data in the literature. Starting at a moderate amplitude, the model is then iterated until the amplification is balanced with the losses in the system. At this stage of balance, the saturation pressure is obtained and the final output acoustic power to the acoustic load is found. Subsequently, parameter studies such as frequency sweeps and altering of the phase of the incoming pressure waves are carried out, to note their effect on the system efficiency.

  • 116. Larsson, G.
    et al.
    Johansson, C. G.
    Saine, K.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Reducing engine noise with an enclosure using micro perforated plate2006Inngår i: EURONOISE - Eur. Conf. Noise Control: Adv. Solutions Noise Control, 2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ship- and power plant combustion engines are complex technical systems that have been spared from noise reducing measures. Since these types of technical systems are commonly placed in sound-insulated rooms or at locations where the emitted sound does not affect people, little effort has been made to reduce the level of noise. The optimal way to reduce noise is at the source, where the sound creating forces are the target of the measure. However, the complexity of an engine makes this a very time consuming project. Described in this paper, the sound is reduced at the sound path, with an enclosure. For an engine, this is a very effective and feasible solution, which also is relatively fast to design and applicable to many different models. The purpose of this enclosure is to reduce sound power from the engine top with 10 dB(A). One part of this project was to construct a mathematical model for the design of an enclosure prototype. The model simulates a three layer wall, consisting of a micro perforated plate (MPP), an absorber and a solid plate and gives as results the absorption and the transmission. The result was confirmed with measurements. By then using classical room acoustics, it is possible to predict the insertion loss of an enclosure. To facilitate the usage of the mathematic model, a stand alone (C++) design application was created. A prototype was manufactured which was tested on the W6L34SG engine. It was tested with loudspeakers and under real condition. This paper describes the mathematical model of the project and also gives result between calculated and measured acoustic quantities.

  • 117.
    Lemne, Jennifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Sack, Stefan
    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.
    Acoustics of micro-perforated orifice plates2018Inngår 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]

    This paper presents a study on the performance of micro-perforated plates (MMP) aimed for application in heating, ventilation and air-conditioning (HVAC) ducts. MPPs are perforated plates with holes or slits in the sub mm range and perforation ratios between 1-10%. When sound waves penetrate the perforation, friction at the hole surfaces leads to acoustic absorption. As MPPs exhibit high flow resistance together with a thin, stiff, and lightweight structure, they can be used to replace internal support structures in flow duct applications to make them acoustically dissipative with small or negligible leakage of flow across the MPP. Here a micro-perforated circular orifice plate is compared to a similar plate without perforation. The comparison is based on measured multi-port data for the plates including both the scattering as well as the flow generated sound.

  • 118. Nashed, M. W.
    et al.
    Elnady, T.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Effect of reflections on HVAC systems power-based acoustic simulation2018Inngår 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]

    Power-based techniques are commonly used in the simulation of the sound propagation in HVAC systems. Sound is generated from supply fan, propagates through the network, experiencing multiple attenuations from different network elements, then it is radiated through the network openings. Several standards (e.g. VDI and ASHRE) describe the attenuation through different HVAC elements and the flow generated noise in other elements. These standards assume no reflections in the network. By neglecting the reflections, the calculation algorithm becomes more easy and robust, but less accurate. However, in a previous work by the authors, the reflection effect was investigated in duct networks, and the results showed that, in several cases, reflections can have a major effect and should not be ignored. This happens when the geometry is complicated with variations in the duct diameter or duct impedance. In this paper, the two-port power-based algorithm is presented after including the reflection effect. The effect of source and outlet impedances is also investigated. The algorithm is validated against FEM simulation on different duct networks built with common duct elements. The results show the effect of reflection on the overall performance of the two-port network, and the influence of diffuse field assumption between elements. 

  • 119.
    Nashed, Mina Wagih
    et al.
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, 1 Elsarayat St, Cairo 11517, Egypt..
    Elnady, Tamer
    Ain Shams Univ, Grp Adv Res Dynam Syst ASU GARDS, 1 Elsarayat St, Cairo 11517, Egypt..
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Modeling of duct acoustics in the high frequency range using two-ports2018Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 135, s. 37-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Design of duct networks is challenging because the design should consider the required flow rate, acceptable noise levels, and minimum pressure drop to achieve optimum performance. This paper presents acoustic analysis in high frequency range using sound power two-ports applied to Heating, Ventilation, and Air Conditioning (HVAC) systems. To simulate the acoustic behaviour one need to model three mechanisms; the sound power generated from sound sources (e.g. Fans), the regenerated sound power caused by the flow in different elements in the network (e.g. junctions), and the sound power loss across different elements of the network. The general approach considered here is based on two-port theory that divides the duct network into two-port elements. Each element can be described by 2 x 2 scattering matrix where the state variables are the acoustic power flow in both up and downstream directions. Junctions and branching are described by multi-port elements depending on the number of elements connected to this multiport. This algorithm is compared to measurements of HVAC system located in an academic building that shows good agreement. An advantage of this approach is the ability to use the same formalism of the two-port network theory to analyse the acoustic behaviour in both low and high frequency ranges beside the flow distribution and the pressure drop.

  • 120.
    Netto Spillere, Andre Mateus
    et al.
    Univ Fed Santa Catarina, Dept Mech Engn, BR-88040900 Florianopolis, SC, Brazil.;Univ Fed Santa Catarina, Acoust & Vibrat Lab, BR-88040900 Florianopolis, SC, Brazil..
    Zhang, Zhe
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, Julio Apolinario
    Univ Fed Santa Catarina, Dept Mech Engn, BR-88040900 Florianopolis, SC, Brazil.;Univ Fed Santa Catarina, Acoust & Vibrat Lab, BR-88040900 Florianopolis, SC, Brazil..
    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. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Optimum Impedance in the Presence of an Inviscid Sheared Flow2019Inngår i: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 57, nr 3, s. 1044-1054Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent years, much effort has been devoted to find the "optimum impedance" (i.e., the impedance that results in the maximum modal decay rate in flow duct acoustics for a given frequency, Mach number, and azimuthal mode order). Although such analysis can be carried out by means of numerical simulations, analytical expressions can also be derived to predict the optimum impedance. Previous works have been concerned with the optimum impedance of higher-order modes in rectangular ducts with uniform flow. In this work, the analysis is expanded to circular ducts for both uniform and sheared inviscid flows. Focus is given to typical operating conditions found in turbofan engine intakes and vehicle exhaust systems. It is shown that, in certain conditions, the optimum impedance is affected even by the presence of a small boundary-layer thickness. It is also noted that, for low Helmholtz numbers, the optimum impedance may have a negative resistance.

  • 121. Okasha, A.
    et al.
    Elnady, T.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic response analysis of pipeline networks 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. 5857-5866Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sound generation and propagation inside pipeline networks has been of major concern in different applications. There is a need to solve performance problems caused by reciprocating equipment or flow generated noise sources in piping and pipeline systems. If the source pulsations coincide with one of the acoustic resonances in the system, high dynamic pressure amplitudes can be generated causing shaking forces at the pipe ends which excite mechanical vibrations and mechanical stress which might lead to fatigue and failure. In this paper, the two-port technique is used to describe the pipeline network where the network can be divided into elements; each is described by a transfer matrix. The compressors are modeled as one-ports described by source strength and source impedance. A pilot plant equipped with a reciprocating compressor was built, and the pressure pulsations were measured in different positions inside the network. The source characteristics of the compressor were measured using the multi-load technique which is commonly used to characterize the acoustics of internal combustion engines. The dynamic pressure was calculated inside the two-port network and compared to the measurements.

  • 122. Okasha, Ahmed
    et al.
    Elnady, Tamer
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Analysis of pipeline networks using two-ports2016Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 109, s. 44-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Majority of vibration problems arise in pipeline networks are attributed to the high-pressure pulsations. Pulsations are generated by fluid machines such as compressors and pumps. These pulsations turn into shaking forces at elements such as pipe bends and pipe reducers, which in turn excite vibrations in the connected piping network. High vibrations beyond the endurance limit of the pipe material may cause damage to pipes, supports, and equipment. In addition, if the source pulsation frequency coincides with one of the natural frequencies of the piping network, resonance will take place and the vibrations will be magnified to a large scale. Obviously, if these vibrations are not well controlled, they might cause damage to the whole system and foundation, and might lead to substantial financial losses. Thus, prediction of pulsations is important for safe and proper operation. In this paper, a pilot plant equipped with a reciprocating compressor, pipes, bends, and terminated by a vessel is built. The network is modeled using the two-port theory that splits the network into several cascaded elements, and predicts the response of the network. The prediction model uses the measured compressor source data as an input, which is determined by the indirect multi-load method that is usually used to characterize internal combustion engines. A pulsation suppression device is designed, modeled, manufactured and inserted into the pilot network. The pressure pulsations are measured with and without the pulsation suppression device, and compared to the predictions using the two-port theory.

  • 123. Orrenius, U.
    et al.
    Betgen, B.
    Feng, Leping
    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.
    Iglesias, E. Latorre
    Thompson, D.
    Brunström, S.
    Rail vehicle source assessment within a virtual certification process2014Inngår i: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2014) AND INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2014), 2014, s. 3511-3525Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The present paper aims at giving an overview of the vehicle noise source modelling work carried out within the Acoutrain FP7 European research project. Results are presented for several areas including: equivalent source modelling concept applied to typical train sources, component based models for aero-acoustic noise generation of pantographs and installation effects of bogie and roof mounted sources. A process to characterize vehicle noise sources in an industrial context is presented. It is shown that equivalent monopole models, for which the source is described by a few monopoles, can be applied to represent real vehicle sources. It is also displayed how analytical models can be used to calculate the insertion loss of screens for sources that can be represented by point sources. Ray tracing and energy BEM models are used to determine the high frequency installation effect of a source in the bogie and a practical, procedure for in-situ testing of installation effects is suggested. For high speed applications a component based model is shown to accurately represent the spectrum of a train pantograph. It is concluded that the results to date are promising but more work is needed to validate the proposed process and methods for real vehicle installations in terms of modelling accuracy and usability in a virtual testing framework for TSI certification purposes.

  • 124. Pedrosa, A. M.
    et al.
    Denia, F. D.
    Fuenmayor, F. J.
    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).
    Experimental measurement of acoustic properties by a two source method with simultaneous excitation2011Inngår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011, 2011, s. 879-886Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, an experimental technique is presented for the acoustic characterization of materials and devices. The developed technique is based on the two source method with simultaneous excitation, thus reducing the time requirements in comparison with the standard two source technique. A decomposition technique is applied to the pressure measurements associated with each microphone, that include noise of two sources acting simultaneously, and the input signals used to excite the two sources. The procedure allows the calculation of the transfer functions between each microphone and each input separately. Once the individual transfer functions have been obtained, it is possible to characterize an acoustic device by means of its four-pole matrix as well as its transmission loss. The technique has been validated by comparison with theoretical results and experimental methods of earlier studies, for several test cases including a straight duct and a reactive muffler.

  • 125.
    Pietroniro, A. G.
    et al.
    Volvo Cars.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. 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.
    Knutsson, M.
    Volvo Cars.
    A Steady-State Based Investigation of Automotive Turbocharger Compressor Noise2018Inngår i: SAE Technical Papers, SAE International , 2018, Vol. 2018-June, nr JuneKonferansepaper (Fagfellevurdert)
    Abstract [en]

    The challenging problem of noise generation and propagation in automotive turbocharging systems is of real interest from both scientific and practical points of view. Robust and fast steady-state fluid flow calculations, complemented by acoustic analogies can represent valuable tools to be used for a quick assessment of the problem during e.g. design phase, and a starting point for more in-depth future unsteady calculations. Thus, as a part of the initial phase of a long-term project, a steady-state Reynolds Averaged Navier-Stokes (RANS) flow analysis is carried out for a specific automotive turbocharger compressor geometry. Acoustic data are extracted by means of aeroacoustics models available within the framework of the STAR-CCM+ solver (i.e. Curle and Proudman acoustic analogies, respectively). This part of the work focuses on the discussion and comparison of the aeroacoustic models, and their suitability towards predicting flow and acoustics trends corresponding to the operating conditions investigated. However, given the unsteady nature of acoustics, the project will have to develop towards an investigation of the problem using more expensive, but more accurate, Large Eddy Simulation (LES) calculations. An entire compressor map with 80 operating conditions was simulated, yielding trends in the behaviour of the performance parameters for the analysed compressor. Detailed results calculated on the same compressor speed-line for one design and one off-design operating conditions are presented in terms of time-averaged pressure coefficient, Mach number, and acoustic power distributions. A total acoustic power map has been generated based on the outcome from the Curle and Proudman acoustic models, giving an indication of the noisiest operating conditions.

  • 126.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Chevalier, M.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    A numerical study of noise characteristics originating from a shrouded subsonic automotive fan2018Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 140, s. 110-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The characteristics of the noise radiated from a reduced automotive cooling module are numerically studied focusing on the interaction effects linked to the sound generation mechanisms and the acoustic scattering caused by the confined installation. The flow field is simulated by adopting the formulation of Improved Delayed Detached Eddy Simulation (IDDES), which is a numerical technique that enables large-scale structures to be resolved and the wall-bounded flow to be treated depending on the turbulent content within the boundary layer. By comparing the simulated fan performance to two sets of measurement data of a similar setup, the aerodynamic results obtained from IDDES are validated and conformed to the volumetric flow rate delivered for the pressure drop measured. The acoustic part of the study comprises evaluation of the sound source associated with the momentum distribution imposed on the surroundings at an interface slightly upstream of the fan. At the microphone positions upstream of the installation, the SPL falls within the SPL range measured and the acoustic power delivered by the fan conforms to the SWL obtained from the comparison method in the reverberation room. The system response function, estimated by subtracting the SWL for the free-field simulation from the SWL associated with the reduced automotive cooling module marks spectral humps at fixed frequencies, irrespectively of sound source. As such, the engineering approach to the spectral decomposition method earlier published, which enables the acoustical properties of the installation to be isolated from the source, is validated and found to hold.

  • 127.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, M.
    Scania AB, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Vibrationsövervakning.
    Acoustic characteristics of a heavy duty vehicle cooling module2016Inngår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 111, s. 67-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.

  • 128.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic characteristics of a heavy duty vehicle cooling moduleManuskript (preprint) (Annet vitenskapelig)
  • 129.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustical Broadband signatures from RANS Turbulence Quantities2014Inngår i: The 21st International Congress on Sound and Vibration, 2014, s. 1541-1548Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The high capacity of today's computers open up the possibility of using numerical simulations to provide a reliable support for optimization of the cooling module placed in heavy vehicles from both an acoustical and aerodynamic perspective. Typically the cooling compartment in heavy trucks consists of a large number of components building a complex, geometrically dense, package. Acoustically, adjacent surfaces are known to modify the sound level and the sound directivity caused mainly by the fan. For this reason, prediction of the sound sources and their radiation, using highly resolved turbulent numerical simulations, is still not feasible. In this paper, we present acoustic predictions that are based on results from Reynolds-Averaged Navier-Stokes (RANS) simulations on a given fan setup with the objective to identify noise characteristics from the turbulent quantities, using analytical expressions derived for isolated airfoils. The analytical formulas give the power spectral density (PSD) in the far-field associated with the noise mechanisms known as incoming turbulence noise and trailing edge noise both caused by the scattering of turbulent structures at the airfoil's leading- and trailing edge, respectively. In the fan setup, the fan was closely mounted to a shroud and placed in a wall between two adjacent rooms. Compared to the intricate underhood engine bay in a truck, the surrounding area affecting the acoustic radiation has been heavily reduced. Emphasis is to seize the apparent broadband trends previously measured in a facility customized for acoustical investigations. The fan studied is running at subsonic speed and consists of 11 blades, having a diameter of 0.75 m. The sound pressure level (SPL) calculated using the analytical expressions was found to show broadband properties previously captured during measurements.

  • 130.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Aeroacoustic calculation using DES together with FW-H for a ducted subsonic fan2014Rapport (Annet vitenskapelig)
  • 131.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania CV, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Quiet and efficient cooling for IC-engine powered systems2013Inngår 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. 5677-5686Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The cooling module placed in heavy vehicles is a compact installation, consisting of several components that all affect the cooling air stream which results in complex flows. Even though the fan is considered the main source of sound, adjacent surfaces affect the flow and the scattering of the sound radiated from the fan and make it difficult to predict the acoustic source distribution and sound field inside and outside of the cooling system. This paper focus on the noise emissions caused by the flow associated with the cooling fan and the interaction with an upstream radiator. The long- Term objective of the work is to obtain an efficient and accurate simulation tool for the design of silent and efficient cooling systems, where the present work will be a viable tool in the evaluation process. A modular test rig was built that consisted of a radiator, shroud, fan and hydraulic engine mounted in a wall, which was located between an anechoic room and a reverberation room in order to control the sound level of the incoming flow. Acoustic characteristics e.g. sound pressure- And sound power levels, have been measured in both rooms and will later be used to validate future numerical simulations.

  • 132.
    Rämmal, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Acoustics of turbochargers2007Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noise from turbo-chargers is increasingly becoming an issue. Partly due to improved noise control of other components and partly due to increased specific mass flows. Despite that the turbocharging technique was developed in the first part of the last century the acoustical behavior is still a field where there is a lack of research. In this paper an overview of the existing research is presented including the work done in the EC-project ARTEMIS. Some first results from recently started investigations at the new gas management research centre, KTH CICERO, will also be described. A turbo-unit always consists of a compressor which normally is driven by an exhaust turbine. Both the turbine and the compressor will have an influence on how the low frequency engine pulsations propagate in the intake/exhaust system. This is referred to as the passive acoustic property of the turbo-unit. If linear acoustic models are applied the passive properties can be described using reflection and transmission coefficients. A turbo-unit will also produce high frequency aerodynamic sound, which is referred to as its active ("sound generating") acoustic property. The sound generation is associated with the rotating blade pressures and for modern turbo-units, with supersonic tip speeds, also with rotating shock waves ("buzz-saw noise").

  • 133.
    Rämmal, Hans
    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.
    Characterization of air terminal device noise using acoustic 1-port source models2007Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 300, nr 05-mar, s. 727-743Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement method to characterize a standard air terminal device as an acoustic 1-port source has been tested and validated. The low-frequency noise generated by flow separation in the device and radiated to a reverberation room has been measured, together with pressure auto- and cross-spectra inside the connected duct. A 1-port source model with parameters derived from the in-duct data was then created. For the source strength part a scaling law was derived showing dipole dependence for the flow speed exponent. To validate the 1-port model and to prove its ability to predict flow noise generation, measurements were performed on a modified duct system.

  • 134.
    Rämmal, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Experimental Determination of Sound Transmission Through Turbo-Compressors2009Inngår i: SAE Technical Paper, no. 2009- 01-2045. May, 2009, 2009Konferansepaper (Fagfellevurdert)
  • 135.
    Rämmal, Hans
    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.
    Experimental determination of sound transmission in turbo-compressors2009Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper experimental procedures to determine the sound transmission through automotive turbo-charger compressors are described. An overview of a unique turbocharger testing facility established at KTH CICERO in Stockholm is given. The facility can be used to measure acoustic two-port data for turbo-compressors. Results from measurements on a passenger car turbo-compressor are presented and the influence of operating conditions on the sound transmission is discussed.

  • 136.
    Rämmal, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Testrig for characterization of turbo-compressor acoustic properties2008Inngår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this paper is to present a description of a novel experimental facility designed for the acoustical 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 experimental procedures for the determination of the scattering data for automotive turbo-chargers at realistic operating conditions will be described. The first experimental results obtained for a Volvo passenger car turbo-compressor are presented for several operating conditions.

  • 137.
    Rämmal, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Tiikoja, Heiki
    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.
    Experimental facility for the complete determination of sound transmission in turbochargers2010Inngår i: SAE Technical Papers, 2010, s. SAE Technical Paper 2010-01-1424-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper a unique experimental facility designed for a complete determination of the sound transmission in turbochargers is introduced. The facility can be used to characterize the passive acoustic effect for turbocharger compressors and turbines working in realistic operating conditions by extracting the acoustic two-port data. The acoustic pressure transmission loss results for a passenger car turbocharger compressor and turbine measured in up- and downstream directions regarding the mean flow are presented. The data are obtained for various operating points of the turbocharger and the influence of operating conditions on the sound transmission is discussed.

  • 138.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Mats, Abom
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Schramz, Christophe
    Kucukcoskunx, Korcan
    Generation and scattering of acoustic modes in ductswith flow2014Inngår i: 20th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The generation and scattering behaviour of fluid machines such as pumps or fans in con-nected duct or pipe systems is of great interest to minimize disturbing and harmful soundemission, for instance of air conditioning systems. One approach to describe the sound-fieldcreated by a fluid machine or in a duct component is to apply a linear multi-port modelthat includes direction-depending transmission and reflection coefficients for the presentwave-modes and the sound generation. Once this characteristic data are determined, thesound-field can be calculated for arbitrary acoustic loads. This paper describes an approachto measure the scattering of the first 8 modes in a duct system with flow, using externalloudspeakers as sound sources.

  • 139.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mats, Åbom
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Experimental characterization of acoustic multi-ports2014Inngår i: Forum Acusticum paper, European Acoustics Association (EAA), 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The generation and scattering behaviour of fluid machines in duct or pipe systems is of great interest to minimize disturbing and harmful sound emission, for instance of air condition systems. In general an in-duct element, e.g., fan, diaphragm, and bend can both generate sound, referred to as the active properties, and scatter sound which is referred to as the passive properties. One approach to describe the sound field created by a fluid machine or in duct components is to apply a linear multi-port model that includes direction-depending transmission and reflection coefficients for the wave-modes and the sound generation. The model parameters can be ascertained either experimentally or numerically.In a first step, a number of external sound fields dominating the existing sound field are applied, in order to determine the system scattering. As the second step, the reflection-free source strength can be computed using the data from the first step. Once the multi-port data are determined, the sound field within the duct can be calculated for arbitrary acoustic loads. This paper discusses an approach to measure the multi-port data in ducts with flow. The method is applied to study a sharp edged orifice as an component for an aircraft climate system with 8 acoustic modes incident on both sides which leads to acoustic multi-ports of the order 16. To perform the measurements loudspeaker and microphone arrays containing 24 sources and 32 microphones were optimized to create well-conditioned matrices to minimize the errors in the resulting multi-port data. The power balance is then applied on the resulting scattering data to evaluate the dissipation of energy from the acoustic field into the vorticity field.

  • 140.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Mats, Åbom
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Numerical Eduction of Active Multi-port Data for In-duct Obstructions2016Inngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 141.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mats, Åbom
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Uncertainty estimation in multi-port measurements2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The generation and scattering behaviour of fluid machines in connected duct or pipe systems isof great interest to minimize disturbing and harmful sound emission, for instance of air condition systems. Within the framework of the European project ’IdealVent’ the acoustic behaviour of airconditioner systems in aircraft is investigated in detail in order to develop strategies to abate sound emission and hence augmenting safety and comfort within the airplane and at the aircraft ramp. One approach to handle such systems is to apply a linear multi-port model that includes direction-depending transmission and reflection coefficients for the propagating wave modes. Those parameters may be ascertained either numerically or experimentally. Once this characteristic data are determined for all elements of interest, the sound scattering and emission behaviour of every considerable com-bination of those elements can be calculated. In order to terminate the system scattering, a numberof external sound fields dominating the existing sound field are applied. This operation consists ofmatrix inversions and wave-number assumptions, which amplify uncertainties induced by the mea-surement procedure. The paper in hand shows a method to estimate the uncertainties for a multi-port of the order 6 by applying a condition number approach and a Monte-Carlo simulation.

  • 142.
    Sack, Stefan
    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.
    Full multi-port characterization of a circular orifice plate2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A multi-port method is used to extract complex mode amplitudes from experimental data of in-duct orifice plates for frequencies with cut-ons of several higher order modes. The two-port method is therefore extended to resolve higher order modes, i.e. spinning modes and radial modes. The work presented in Sack et all.1 is continued and a new test- rig design is presented which enables more stable measurements and cleaner data. The scattering and source data for higher order modes of a circular sharp-edged orifice plate with low Mach-number mean flow is presented and used for advanced post-processing. The gained data is used to predict the scattering of a tandem orifice configuration and the prediction is compared to measurement results.

  • 143.
    Sack, Stefan
    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.
    Modal filters for in-duct sound based on the cremer impedance and micro-perforated plates2016Inngår i: Proceedings of the INTER-NOISE 2016 - 45th International Congress and Exposition on Noise Control Engineering: Towards a Quieter Future, German Acoustical Society (DEGA) , 2016, s. 3215-3222Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The design of a new filter-type is presented that allows a sufficient reduction of in-duct aero-acoustic noise. The filter is a hybrid design containing a lined duct section based on the so called Cremer impedance and a section with combinations of micro-perforated plates. The Cremer impedance section strongly damps the zero-order or plane wave mode while the MPP section which breaks the circumferential symmetry of the duct and damps the higher order modes. Different designs are investigated numerically, solving the linearized Navier-Stokes equations in the frequency domain and decomposing the sound-field into its modal components. Both, the transmission loss and the total power loss is calculated and compared for different assemblies and plate impedances.

  • 144.
    Sack, Stefan
    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.
    Modal Filters for Mitigation of In-duct Sound2016Inngår i: Proceedings of Meetings on Acoustics, American Institute of Physics (AIP), 2016, Vol. 29, nr 040004, artikkel-id 040004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Investigations on noise mitigation strategies for duct systems with a low number of propagating modes, as found in middle size HVAC systems, are sparse. Here, the design of a silencer is presented based on cascades of modal filters and a Cremer silencer. The modal filter aims at mitigating spinning duct modes. The Cremer silencer is a silencer that realizes impedance for optimal attenuation for the plane wave at one frequency (Cremer impedance). The combination of both can create high damping both for planar and non-planar waves. The modal filter consists of micro-perforated plates parallel to the duct axis in mean flow direction. As the concept of modal filters is unprecedented, general investigations of its acoustic behaviour are carried out by solving the Helmholtz equation numerically to investigate the effect of different plate positions, the number of plates and the plate impedance on the acoustic absorption. Finally, the combination of the Cremer silencer and the modal filter is investigated by performing measurements on prototypes. It is shown, that even though the damping of the modal filter is low compared to the Cremer silencer, improved damping and dissipation of fields consisting of plane waves and spinning modes can be achieved by combining the two types.

  • 145.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    On Acoustic Multi-Port Characterisation Including Higher Order Modes2016Inngår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 192, nr 5, s. 834-850Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Methods to design test-procedures for acoustic multi-ports in ducts with a focus on pressure sampling positions for accurate modal decomposition are demonstrated. Acoustic fields up- and downstream of an in-duct acoustic element are excited by external sources and decomposed into transmitted and reflected aeroacoustic modal pres- sure amplitudes in order to first determine the acoustic scattering of the element. Secondly, the determination of the element source strength requires tests with no external sources, but with known terminations and scattering data. Unfavourable source and sensor positions lead to mode coupling and to ill-conditioned or even singular decomposition matrices, which results in high amplifications of uncertainties within the wave decomposition. An unoptimised but over-determined assembly is compared with a setup containing a minimum of sensors but with optimised positions. Lower uncertainty amplification, despite the usage of fewer sensors, is achieved for most frequencies, especially after the cut-on of t he higher order acoustic modes. A genetic algorithm (GA) is used to achieve this optimised setup by minimising the condition number of the decomposition matrix, which is a multi-dimensional optimisation problem with numerous local minima. To estimate the stability of the optimised configuration, a Monte-Carlo Method (MCM) is deployed to introduce normal distributed complex pressure un- certainties into the decomposition. In order to estimate the wave number, different approaches are compared - namely the classical non-dissipative wav e number estimate, an extended Kirchhoff method for viscous-thermal damping and an eigenvalue solution of the Linearised Navier Stokes Equations by Dokumaci. The presented de- composition method is not only applicable to measurement data but is equally useful to post-process results from numerical computation.

  • 146. Shur, M.
    et al.
    Strelets, M.
    Travin, A.
    Christophe, J.
    Kucukcoskun, K.
    Schram, C.
    Sack, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Effect of inlet distortions on ducted fan noise2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The paper presents an investigation of flow and noise produced by a generic ECS fan installed in a circular duct. A focus of the study is the evaluation of the effect of mean flow distortions and elevated turbulence levels upstream of the fan, here created by replacing a baseline smooth bell-mouth duct inlet by inlets with a rectangular-to-circular transition of the duct cross-section and with a T-junction formed by two circular pipes. The study includes both experiments which are aimed primarily at supplying data for a validation of simulation approaches and numerical simulations based on a hybrid RANS-LES approach (Improved Delayed Detached Eddy Simulation – IDDES) combined with an “injection” of resolved turbulent content upstream of the fan with the use of an acoustically adapted volumetric synthetic turbulence generator. Acoustic modal decomposition of the measured and computed unsteady pressure fields is then carried out based on the latest developments of a linear multi-port acoustic approach. This allows extracting “pure” (with filtered out hydrodynamic/turbulent fluctuations) acoustic modes propagating upstream and downstream of the fan under reflection-free conditions. Visualizations of simulation results are presented revealing a wide range of resolved turbulent vortices responsible for the broadband noise. A detailed comparison with experiment is carried out for both the “raw” pressure spectra on the duct walls and the individual acoustic modes propagating along the duct in the upstream and downstream directions. It is shown that in terms of acoustics, a replacement of the clean inlet by the rectangular-circular one is almost neutral, whereas the use of the T-junction inlet causes a strong noise penalty.

  • 147. Spillere, A. M. N.
    et al.
    Zhang, Zhe
    KTH.
    Cordioli, J. A.
    Åbom, Mats
    KTH.
    Bodén, Hans
    KTH.
    Optimum impedance in the presence of an inviscid sheared flow2018Inngår i: 2018 AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2018, artikkel-id AIAA 2018-3777Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In recent years, much effort has been devoted to find the “optimum impedance” i.e. the impedance that results in the maximum modal decay rate in flow duct acoustics. Although such analysis can be carried out by means of numerical simulations, analytical expressions can also be derived in order to predict the optimum impedance. Previous works have been concerned over the optimum impedance of higher order modes in rectangular ducts with uniform flow. In this work, the analysis is expanded to circular and rectangular ducts for both uniform and sheared inviscid flows. Focus is given on a typical aero-engine intake and flight conditions. It is shown that, in certain conditions, the optimum impedance is affected even by the presence of a small boundary layer thickness. It is also noted that for low Helmholtz numbers the optimum impedance may have a negative resistance.

  • 148.
    Temiz, M. A.
    et al.
    Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, The Netherlands.
    Arteaga, I. L.
    Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, The Netherlands.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hirschberg, A.
    Eindhoven University of Technology, Department of Applied Physics, Eindhoven, The Netherlands,.
    Acoustic end correction in micro-perforated plates - Revisited2014Inngår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, s. 1203-1209Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Micro-Perforated plates (MPP) are plates with a porosity of the order of 1% in which the perforation diameter is optimized for absorption of incident acoustic waves. The concept has been introduced by Maa[1], who proposed an analytical model based on the solution for the oscillating viscous flow in a long capillary tube. The finite length of the geometry is taken into account by reactive and resistive end-corrections of Ingard[2]. In order to match experimental data, the single sided resistive end correction of Ingard has been multiplied by a factor a. This factor varies in the literature in the range 2 ≤ α ≤ 4. Bolton and Kim[3] propose the use of CFD to determine these end-corrections. Using a similar approach, our present work proposes an alternative result to their work. We use a linear numerical model based on incompressible Navier-Stokes equations in 2D-axisymmetric coordinates, which is solved in the Fourier domain, rather than the time domain simulation as proposed by Bolton and Kim. Working in the Fourier domain with linearized equations ensures the numerical efficiency and absence of non-linear effects. We furthermore use an alternative procedure to determine the inertial part of the transfer impedance leading to a difference of the order of 10% with the results of Bolton and Kim. Moreover, our results show that resistive and reactive end corrections are mainly a function of the Shear number Sh. The porosity a and plate thickness to perforation diameter ratio t∗ seems to be less important.

  • 149.
    Temiz, Muttalip Askin
    et al.
    Eindhoven University of Technology, Department of Mechanical Engineering, Dynamics and Control, The Netherlands.
    Arteaga, Ines Lopez
    Eindhoven University of Technology, Department of Mechanical Engineering, Dynamics and Control, The Netherlands.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Hirschberg, Avraham
    Eindhoven University of Technology, Department of Applied Physics, Gas Dynamics and Aero-Acoustics, The Netherlands.
    The influence of edge geometry on end-correction coefficients in micro perforated plates2015Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 138, nr 6, s. 3668-3677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Global expressions are proposed for end-correction coefficients in micro perforated plates (MPPs) using non-dimensional parameters. MPPs are sound absorbers with small perforation diameters such that the Stokes boundary layers fill up almost the entire perforation. Sound absorption does not only occur within the perforation, but also takes place just outside of it. The latter contribution plus the outside inertia effect on the transfer impedance of the MPP are referred to as end-corrections. In order to determine them, an analytical solution employing the very thin Stokes layer assumption has been derived. However, this assumption requires empirical coefficients in the end-corrections for accurate results. To explore the effects of various parameters a numerical model is used. This model is verified with open-end reflection coefficient measurements. The most prominent result from this study is that compared to plate thickness, the ratio of perforation diameter to Stokes layer thickness (Shear number) and edge geometry affect the end-correction coefficients more significantly. The effect of plate thickness can be neglected for practical purposes, therefore, expressions for the end-corrections in terms of Shear number and edge geometry are provided. The relative error of these expressions is <3% compared to the numerical results. 

  • 150.
    Tiikoja, H.
    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, MWL Marcus Wallenberg Laboratoriet.
    Rämmal, H.
    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).
    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).
    Investigations of automotive turbocharger acoustics2011Inngår i: SAE technical paper series, ISSN 0148-7191Artikkel 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. Copyright 

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