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  • 1.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    CFD of Duct Acoustics for Turbocharger Applications2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. In this work the main focus is the turbocharger compressor and a discussion of turbocharger acoustics and earlier work within the area is presented, giving an insight into its sound generating mechanisms and the damping effect it has on pressure pulses, i.e. incoming waves. However, despite the fact that turbo-charging was developed during the first part of the 20th century, there is not much research results available within the area of centrifugal compressor acoustics.

    To improve the understanding of the acoustics of engine duct components, methods based on compressible Large Eddy Simulation (LES) are explored. With these methods it is possible to capture both the complex flow, with sound generating mechanisms, and acoustic - flow interactions. It is also possible to get a detailed insight into some phenomena by access to variables and/or areas where it is difficult to perform measurements. In order to develop these methods the linear scattering of low frequency waves by an orifice plate have been studied, using an acoustic two-port model. This simple geometry was chosen since the flow has several of the characteristics seen in a compressor, like unsteady separation, vortex generation and shock waves at high Mach numbers. Furthermore the orifice plate is in itself interesting in engine applications, where constrictions are present in the ducts. The results have been compared to measurements with good agreement and the sensitivity to different parameters has been studied, showing an expected dependence on inlet Mach number and difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the short times series available in LES. 

    During the development of new engines the industry uses 1D engine CFD tools. These tools are developed to give performance data, but sometimes also the acoustic pulsations are studied. The duct components are modelled and the turbocharger is often modelled with a map, representing its fluid mechanical properties measured under steady state conditions. An aim in this work has been to study the limitations of the models available in the commercial software GT-Power. The scattering of incoming waves was simulated and the results were compared to measurements, showing a large discrepancy for the compressor and a significant discrepancy for the orifice plate.

  • 2.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Flow Duct Acoustics: An LES Approach2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. Simulations are an important tool for enhanced understanding; they give insight into the flow-acoustic interaction in components where it is difficult to perform measurements. In this work the acoustics is obtained directly from a compressible Large Eddy Simulation (LES). With this method complex flow phenomena can be captured, as well as sound generation and acoustic scattering.

    The aim of the research is enhanced understanding of the acoustics of engine gas exchange components, such as the turbocharger compressor.In order to investigate methods appropriate for such studies, a simple constriction, in the form of an orifice plate, is considered. The flow through this geometry is expected to have several of the important characteristics that generate and scatter sound in more complex components, such as an unsteady shear layer, vortex generation, strong recirculation zones, pressure fluctuations at the plate, and at higher flow speeds shock waves.

    The sensitivity of the scattering to numerical parameters, and flow noise suppression methods, is investigated. The most efficient method for reducing noise in the result is averaging, both in time and space. Additionally, non-linear effects were found to appear when the amplitude of the acoustic velocity fluctuations became larger than around 1~\% of the mean velocity, in the orifice.

    The main goal of the thesis has been to enhance the understanding of the flow and acoustics of a thick orifice plate, with a jet Mach number of 0.4 to 1.2. Additionally, we evaluate different methods for analysis of the data, whereby better insight into the problem is gained. The scattering of incoming waves is compared to measurements with in general good agreement. Dynamic Mode Decomposition (DMD) is used in order to find significant frequencies in the flow and their corresponding flow structures, showing strong axisymmetric flow structures at frequencies where a tonal sound is generated and incoming waves are amplified.The main mechanisms for generating plane wave sound are identified as a fluctuating mass flow at the orifice openings and a fluctuating force at the plate sides, for subsonic jets. This study is to the author's knowledge the first numerical investigation concerning both sound generation and scattering, as well as coupling sound to a detailed study of the flow.With decomposition techniques a deeper insight into the flow is reached. It is shown that a feedback mechanism inside the orifice leads to the generation of strong coherent axisymmetric fluctuations, which in turn generate a tonal sound.

  • 3.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sound Generating Flow Structures in a Thick Orifice Plate Jet2014In: Progress in Turbulence V: Proceedings of the iTi Conference in Turbulence 2012, Cham, Switzerland: Springer, 2014, p. 201-204Conference paper (Refereed)
    Abstract [en]

    The aim of thiswork is to study sound generating flowstructures in a thickcircular orifice plate jet, placed in a circular duct. Large eddy simulations (LES)are performed for two jet Mach numbers, 0.4 and 0.9. Characteristic frequenciesin the flow, and their corresponding flow structures, are identified with dynamicmode decomposition (DMD). The results show that a tonal noise is generated atfrequencies where the jet displays strong ring vortices, in the plane wave range.The main sound generating mechanisms seems to be a fluctuating mass flow at theorifice opening and a fluctuating surface force at the plate sides, caused by the ringvortices. The frequencies are believed to be chosen, and strengthened, by a feedbackmechanism between the orifice in- and outlet.

  • 4.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Large eddy simulations of acoustic-flow interaction at an orifice plate2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 345, p. 162-177Article in journal (Refereed)
    Abstract [en]

    The scattering of plane waves by an orifice plate with a strong bias flow, placed in a circular or square duct, is studied through large eddy simulations and dynamic mode decomposition. The acoustic-flow interaction is illustrated, showing that incoming sound waves at a Strouhal number of 0.43 trigger a strong axisymmetric flow structure in the orifice in the square duct, and interact with a self-sustained axisymmetric oscillation in the circular duct orifice. These structures then generate a strong sound, increasing the acoustic energy at the frequency of the incoming wave. The structure triggered in the square duct is weaker than that present in the circular duct, but stronger than structures triggered by waves at other frequencies. Comparing the scattering matrix with measurements, there is a good agreement. However, the results are found to be sensitive to the inflow, where the self-sustained oscillation in the circular duct simulation is an artefact of an axisymmetric, undisturbed inflow. This illustrates a problem with using an undisturbed inflow for studying vortex-sound effects, and can be of interest when considering musical instruments, where the aim is to get maximum amplification of specific tones. Further, it illustrates that at the frequency where an amplification of acoustic energy is found for the orifice plate, the flow has a natural instability, which is suppressed by non-axisymmetry and incoming disturbances.

  • 5.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    LES of Acoustic-Flow Interaction at an Orifice Plate2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Conference paper (Other academic)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with flow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency ($St \approx 0.4$). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fluctuations.

  • 6.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Scattering of Plane Waves by a Constriction2011In: Proceedings of ASME Turbo Expo 2011, Vol 7, Parts A-C, American Society Of Mechanical Engineers , 2011, p. 1043-1052Conference paper (Refereed)
    Abstract [en]

    Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

  • 7.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Helwan University, Egypt.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Methods for Accurate Determination of Acoustic Two-Port Data in Flow Ducts2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Accurate measurement of the acoustic two port data can be used not only to determine the transmission loss but also to determine physical properties like flow resistivty as well as speed of sound and impedance. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. Techniques to improve the acoustic two-port determination have been tested in this paper. A number of possible configurations for connecting loudspeakers to the flow duct have been investigated. It was found that using a perforate pipe section with about 50% porosity between the loudspeaker side branch and the duct gave the best signal-to-noise ratio out of the studied configurations. Different signal processing techniques have been tested for reducing the adverse effects of flow noise at the microphones. The most successful techniques require a reference signal which can be either the electric signal being input to the loudspeakers or one of the microphone signals. As a reference technique stepped sine excitation with cross-spectrum based frequency domain averaging was used. This technique could give good results for most cases. Using a periodic signal (saw-tooth) and synchronised time domain averaging good results could be obtained if a sufficient number of averages was used. At flow velocities higher than M=0.2 about 10000 averages were needed. Random excitation together with cross-spectrum based frequency domain averaging also gave good result if the same number of averages was used. Ordinary frequency domain averaging is not sufficient at high flow velocities. It was also shown that using cross-spectrum based frequency domain averaging an improvement could be obtained if the microphone with the highest signal-to-noise ratio at each frequency was used as the reference microphone rather than a fixed microphone.

  • 8.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Over-determination in acoustic two-port data measurement2006In: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The plane wave acoustic two-port is a 2x2 matrix containing 4 complex quantities at each frequency. To experimentally determine these unknowns the acoustic state variables on the inlet and outlet side must be measured for two independent test cases. The two independent test cases can be created by: changing the acoustic load on the outlet side leading to the so-called two-load technique or by using one acoustic source on the inlet side and one acoustic source on the outlet side leading to the so-called two-source technique. In the latter case the independent test cases are created by first using the source on the inlet side and then the source on the outlet side. As pointed out by Åbom it is also possible to run both sources simultaneously to create more than two independent test cases. This over-determination could be used to improve the measurement results for instance if the data is contaminated by flow-noise. In this paper over-determination is tested by applying up to 5 different test cases. This procedure has been applied to a single orifice test object.

  • 9. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    A New Type of Muffler Based on Microperforated Tubes2011In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 133, no 3, p. 031005-Article in journal (Refereed)
    Abstract [en]

    Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (similar to 400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e. g., for use in automotive exhaust or ventilation systems, is investigated.

  • 10.
    Berglund, Per-Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    An application of the noise synthesis technology (NST) to a system with an axial fan2002In: Forum Acustica 2002, Seville, Spain, 2002Conference paper (Refereed)
  • 11.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Experimental investigation of harmonic interaction effects for perforates2005In: Collection of Technical Papers: 11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, 2005, Vol. 2, p. 1236-1242Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of a small experimental study of acoustic non-linear harmonic interaction effects for perforates. Impedance measurements using multiple pure tone excitation has been used. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

  • 12.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    In-duct source characterization for multiple sources2009In: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, p. 2664-2671Conference paper (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for detecting if there are multiple sources in a duct and obtaining the acoustic characteristics of these sources. Experimental techniques for in-duct source characterization under plane wave conditions in ducts, when we know the location of the source, are well established. In some cases there can however be sources at both ends of a duct. The paper starts with discussing the possibility to, by using a number of flush mounted microphones in the duct, detect sources located on both sides of the test section and to extract the acoustic source characteristics of the sources. First the sound field in a duct with sources at both ends is discussed and described. The theory for experimental determination of source data is then described. A discussion of the consequences of source correlation is included. The methods are first tested using loudspeakers in a duct.

  • 13.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    International Journal of Aeroacoustics, volume 6, number 12007Collection (editor) (Refereed)
    Abstract [en]

    In November 2005 a Workshop with the title ”Active Control of Aircaft Noise – Concept to Reality” was organised by CEAS-ASC (Council of European Aeronautical Societies – Aeroacoustics Specialist Committee). The Workshop was held at KTH (the Royal Institute of Technology) in Stockholm, Sweden and was chaired by Hans Bodén from KTH and Urban Enborg from A2 Acoustics. This was the ninth in a series of annual Workshops organised by CEAS-ASC. It was co-sponsored by_the American Insitute of Aeronautics and Astronautics (AIAA), CARAN SAAB Engineering, SAAB, Airbus, KTH and the EU through the X2-Noise Thematic Network.

                A total of 20 papers were presented during the two day event divided into four sessions: interior noise, airframe noise flow control, jet noise and fan noise.

                The aim of the Workshop was to summarise the state of the art and to indentyfy breakthroughs needed in order to apply active control in reducing aircraft noise. The technique is most mature in control of interior noise where there are 850 systems flying in regional turnoprop aircraft , business turboprop and some jet aircraft and military aircraft. There has been a lot of work on active control of fan noise both on active liners and using flow control to reduce fan tone noise and active control of buzz saw noise. Also for airframe noise there have been studies e.g., on applying active flow control to highlift devices. Closed-loop flow control has been used in control of cavity tones. Studies have also been made of the use of flow injection for reduction of jet noise. Another technique tested for jet noise reduction is deployable chevrons.

    The present issue contains five of the twenty papers presented at he Workshop. The selection is slanted towards active control of fan noise with two papers on the interesting subject of buzz saw noise reduction, one paper on control of fan tone noise using flow induction and one paper on hybrid passive/active treatment for inlet nacelles. In addition, there is one paper on optimisation of interior noise control.

  • 14.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    On impedance measurements for samples with non-linear acoustic properties2008In: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, BC, 2008Conference paper (Refereed)
    Abstract [en]

    This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. The paper starts with a short review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested.

  • 15.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties2012In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 13, p. 3050-3067Article in journal (Refereed)
    Abstract [en]

    Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated.

  • 16.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Single tone excitation techniques for determination of non-linear acoustic properties of perforates2010In: Proceedings of the International Conference on Noise and Vibration Engineering, ISMA 2010, 2010, p. 597-609Conference paper (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New single sided and double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested.  The results of the preliminary experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 17.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Study of nonlinear energy transfer for perforated wall treatment using acoustic source characterisation techniques2011In: 18th International Conference on Sound and Vibration (ICSV18), 2011Conference paper (Other academic)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates used in aircraft engine liners and automotive mufflers. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems. Nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea here is that these sources can be characterised using linear one-port techniques which are traditionally used for obtaining source data for in-duct sources such as fans or IC-engines. The results of the experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 18.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Two-Port Techniques For Characterisation Of Non-Linear In-Duct Sources2008In: 15th International Congress on Sound and Vibration (ICSV15), 2008Conference paper (Other academic)
    Abstract [en]

    This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers.  It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Non-linear wave propagation and wave steepening are not taken into account. The paper starts with a review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. The effect of using different types of excitation and non-linear harmonic interaction mechanisms are discussed. Experiments were previously made using both pure tone and random excitation and the relevant parameters controlling the non-linearity were discussed. A study of harmonic interaction effects using two-tone excitations was made and later extended to multi-tone excitation for different types of perforates. In the linear case the impedance is independent of the sound field but when the sound pressure level is high the perforate impedance will be dependent on the acoustic particle velocity in the holes. For pure tone excitation it is usually assumed that the impedance will be controlled by the acoustic particle velocity at that frequency, even though the non-linearity will in fact cause energy to be transferred to other frequencies. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency may depend on the particle velocity at other frequencies. The results show that the total rms-value of the particle velocity in the holes seems to be the relevant parameter controlling the non-linearity. A study was previously made of using non-linear system identification techniques for this purpose. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed in the present paper. These new techniques take the non-linear energy transfer into account. 

  • 19.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Holmberg, Andreas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Experimental Techniques for Aeroacoustics in Low Mach Number Confined Flows: Keynote Paper2011In: Proceedings of the International Conference on Mechanical Engineering 2011(ICME2011) 18-20 December 2011, Dhaka, Bangladesh, ICME , 2011Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications such as in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The wall mounted pressure transducers normally used will pick up unwanted flow noise mainly in the form of turbulent pressure fluctuations. The problem is then obtaining a signal-to- noise ratio high enough for quality measurements. Techniques to improve acoustic two-port determination have been developed in this paper, including test rig design, signal processing techniques and over-determination.

  • 20.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Aslan, Johan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Yousif, Michel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A study of annoyance caused by ground based activities at Bromma airport2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    Bromma airport is located nearby the city centre of Stockholm Sweden. There are a number of residential areas around the airport. The paper reports results from a measurement campaign and a questionnaire survey investigation among the people living in the area Bromma kyrka, located approximately 500 meters from the airport. The objective of the study was to identify the most annoying sound sources related to ground activities at the airport. This means that the noise events caused by starting and landing airplanes were identified using information from the airport, so that they could be separated from the noise caused by ground based activities. The survey showed that the most annoying ground based noise sources within the airport wee, airplane warm ups and airplane taxiing. Starting and landing airplanes were also important source of annoyance. The most important source of noise annoyance from outside the airport boundaries was road traffic. The results from the survey were compared with the measured noise levels giving reasonable correlation between recorded high noise level events and logged annoyance events.

  • 21.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Eslami, Armin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Determination of non-linear acoustic properties of perforates using single tone excitation2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples accessible from both side such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested.  The results of the preliminary experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 22.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Guo, Ying
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Tözün, Hüseyin Bora
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental investigation of nonlinear acoustic properties for perforates2006In: Collection of Technical Papers: 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 2006, Vol. 1, p. 67-74Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of a study of non-linear acoustic properties of perforates and micro-perforates. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. In the linear limit the perforate acoustic impedance is independent of the sound field but when the sound pressure level is high it will be dependent on the acoustic particle velocity in the holes. For pure tone excitation the impedance will be controlled by the acoustic particle velocity at that frequency. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency will depend on the particle velocity at other frequencies. In this paper a study lias been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.

  • 23.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Torregrosa, A.
    Ollivier, F.
    Peat, K.
    Fairbrother, R.
    Henriksson, B.
    Recouvreur, P.
    Poullard, O.
    Glav, Ragnar
    Scania AB, Sweden.
    Lavrentjev, J.
    Noise from turbo-charged diesel engine exhaust systems2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 2231-2238Conference paper (Refereed)
    Abstract [en]

    This paper summarises the main results of an EU-funded research project, ARTEMIS (G3RD-CT-2001-00511), on noise from turbo-charged Diesel engine exhaust systems. The project started in September 2001 and ended in August 2004 and was co-ordinated by KTH. The project had 10 partners from 6 different European countries, 5 universities and 5 companies including some major truck and car manufacturers. The main objective was to develop new and improved computational tools for predicting noise from exhaust systems. New models for describing the engine as an acoustic source were developed and experimentally tested. They include a linear time-varying source model and a non-linear frequency domain model. Linear time-invariant source data was also determined both from experiments and using 1-D gas-exchange simulations. New and improved models were developed for the turbo-group including non-linear time domain models and a linear time-varying model. New models were developed and experimentally tested for sound transmission through the Diesel particulate filter included in modern Diesel engine after-treatment devices. Improved models were developed for describing perforate mufflers with high mean flow velocities. Improved experimental techniques for determination of transmission properties of duct system components were developed. Models were developed and coded for sound reflection and radiation from tailpipe openings. Full experimental validation of the Munt theory for radiation from open pipes with flow was produced. In conclusion it can be said that the project was successful and gave many useful results.

  • 24.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    An analysis of the acoustic energy in a flow duct with a vortex sheet2009In: MATHEMATICAL MODELING OF WAVE PHENOMENA / [ed] Nilsson B; Fishman L; Karlsson A; Nordebo S, 2009, Vol. 1106, p. 130-139Conference paper (Refereed)
    Abstract [en]

    Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow-acoustic interaction. One way to quantify the interaction is to study the energy in the incident and the scattered field respectively. If the interaction is strong, energy may be transferred between the acoustic and the main flow field. In particular, shear layers, that may be transferred between the acoustic and the main flow field. In particular, shear such as acoustic waves. The vortex sheet model is an analytical linear acoustic model, developed to study scattering of acoustic waves in duct with sharp edges including the interaction with primarily the separated flows that arise at sharp edges and corners. In the model the flow field at an area expansion in a duct is described as a jet issuing into the larger part of the duct. In this paper, the flow-acoustic interaction is described in terms of energy flow. The linear convective wave equation is solved for a two-dimensional, rectangular flow duct geometry. The resulting modes are classified as "hydrodynamic" and "acoustic" when separating the acoustic energy from the part of the energy arising from the steady flow field. In the downstream duct, the seat of modes for this complex flow field are not orthogonal. For small Strouhal numbers, the plane wave and the two hydrodynamic waves are all plane, although propagating with different wave speeds. As the Strouhal numbers increases, the hydrodynamic modes changes to get a shape where the amplitude is concentrated near the vortex sheet. In an intermediate Strouhal number region, the mode shape of the first higher order mode is very similar to the damped hydrodynamic mode. A physical interpretation of this is that we have a strong coupling between the flow field and the acoustic field when the modes are non-orthogonal. Energy concepts for this duct configuration and mean flow profile are introduced. The energy is formulated such that the vortex sheet turns out as a sink for the acoustic field, but a source for the unstable hydrodynamic were. This model is physical only close to the edge, due to an exponentially growing hydrodynamic mode. In a real flow, non-linearities will limit the growth, but this is not included in the model.

  • 25.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Kedhammar, Anders
    Nilsson, Mats E.
    The Influence of Background Sounds on Loudness and Annoyance of Wind Turbine Noise2012In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 98, no 5, p. 741-748Article in journal (Refereed)
    Abstract [en]

    Natural sounds may create pleasant soundscapes that mask wind turbine noise. To explore this, a listening test was performed to investigate the influence of background sounds on perceived loudness and annoyance of wind turbine noise. A magnitude estimation method was used to measure perceived loudness and annoyance of wind turbine noise heard together with and without natural ambient sounds. Results indicate that decreased loudness and annoyance occurs if the level of the background sound exceeds the level of the wind turbine noise. The loudness experiment revealed that ambient sounds influenced the perception of wind turbine noise to a higher degree than predicted from a model of energetic masking. Annoyance ratings were less altered by background sound than perceived loudness. The results of the present listening study indicates that masking of wind turbine noise by positive natural sounds may be used as a complement to conventional noise control measures to improve the sound environment in areas exposed to wind turbine noise.

  • 26.
    Chowdhury, S.C.
    et al.
    BUET.
    Razzaque, M.M.
    BUET.
    Helali, M.M.
    BUET.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Assessment of noise pollution in Dhaka city2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    Like many other mega cities of developing countries, noise pollution in Dhaka city of Bangladeshis a big concern. Here noise is produced from different sources like traffic, loudspeaker,people gathering etc. To mitigate the noise pollution in Dhaka city, the governmentof Bangladesh has recently passed a new ordinance and has modified the existing traffic controlrules. However, the condition did not improve as much as expected. Exposure to highlevel noise may cause severe stress on the auditory and nervous system of the city dwellers,particularly the children. The extreme effects e.g. deafness and mental breakdown are alsooccasionally reported. This paper reports the level of noise pollution in Dhaka city. For thispurpose noise levels have been measured at ten major locations of the city from 8 AM to 10PM during the working days. The data have been analyzed to calculate various noise parameterssuch as Leq, and Lnp. It is observed that at all the locations, the level of noise remains farabove the acceptable limit for all the time. Comparison of present results with the existingprevious results shows that noise level in the Dhaka city is increasing day by day. The papersuggests that urgent measures should be taken into consideration to control the level of noisepollution in the city and vulnerable institutions like kinder gardens, schools and hospitalsshould be located far away from the road side.

  • 27.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Pieper, Timm
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Simulation of Wave Scattering at an Orifice by using a Navier-Stokes Solver2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007, 2007Conference paper (Other academic)
  • 28. El Bardisi, M.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Sources of noise in greater Cairo: example East Cairo2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 3481-3488Conference paper (Refereed)
    Abstract [en]

    Noise in big cities such as Cairo Egypt is an important pollutant in the modern society. Noise coming from airports, road traffic, rail traffic, power plants as well as commercial activities in the city are important contributors to the overall noise level. A noise study including measurements and predictions for noise in East Cairo coming from airport, road traffic, metro and railways was performed and analyzed. A comparison of the different sources was made and the number of affected people in the mentioned area was estimated. The dominating sources and the best mitigation to minimize the noise level was discussed and evaluated. In the analysis, some new projects was discussed individually to find its effect on noise pollution, also expectation for the coming years with the new projects and proposals where discussed. The proposed new projects include the new terminal building and runway at Cairo international airport and the proposed Heliopolis Metro Line-4 Ramsis Square - Nasr City. The analysis showed the dominating noise sources and evaluated the mentioned projects from the noise point of view. Noise out from air traffic was the dominating source of noise in East Cairo.

  • 29.
    El Nemr, Yasser
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Acoustic modeling and testing of exhaust and intake system components2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Intake and exhaust orifice noise contributes to interior and exterior vehicle noise. The order noise radiated from the orifice of the intake and exhaust systems is caused by the pressure pulses generated by the periodic charging and discharging process and propagates to the open ends of the duct systems.

    The propagation properties of these pulses are influenced by the dimensions and acoustic absorption properties of the different devices in the intake/exhaust line (muffler, turbocharger, catalyst, intercooler, particulate filter, etc.). Additional to this pulse noise, the pulsating flow in the duct system generates flow noise by vortex shedding and turbulence at geometrical discontinuities.

    Several turbochargers, catalytic converters, Diesel particulate filters and intercoolers elements were investigated and analyzed by performing two-port acoustic measurements with and without mean flow at both cold conditions (room temperature) and hot conditions (running engine test bed) to investigate these devices as noise reduction elements. These measurements were performed in a frequency range of 0 to 1200 Hz at no flow conditions and at flow speeds: 0.05 and 0.1 Mach.

    A new concept for the acoustic modeling of the catalytic converters, Diesel particulate filters and Intercoolers, and a new geometrical model for the turbocharger were developed. The whole test configuration was modeled and simulated by means of 1-D gas dynamics using the software AVL-Boost. The results were validated against measurements. The validation results comprised the acoustic transmission loss, the acoustic transfer function and the pressure drop over the studied test objects. The results illustrate the improvement of simulation quality using the new models compared to the previous AVL-Boost models.

  • 30. Elnady, T.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Elhadidi, B.
    Validation of an Inverse Semi-Analytical Technique to Educe Liner Impedance2009In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 47, no 12, p. 2836-2844Article in journal (Refereed)
    Abstract [en]

    In this paper, the acoustic impedance of a liner is educed by a novel semi-analytical inverse technique. The liner sample is placed flush with the solid walls in a rectangular duct with grazing flow. The technique uses complex acoustic pressure measured at four positions at the wall of the duct, upstream and downstream of the lined section, and educes the impedance with a mode-matching method. Previous studies neglected grazing flow nonuniformity and the pressure discontinuity that appears at the liner-wall boundary caused by the discontinuity of the acoustic particle velocity into the wall. In the present paper, the mode-matching formulation is rederived in terms of pressure instead of velocity potential which is found to be more numerically stable. Moreover, the proposed methodology is validated with benchmark data from an experiment performed by NASA. First, the ability of the code to reproduce the pressure field for a given impedance is tested. Second, the ability to educe the correct impedance for a given pressure distribution is tested. The results of the mode-matching code are in very good agreement with the experimental data. The effect of shear flow is investigated and it can be concluded that the assumption of uniform flow is appropriate for the chosen liner, duct size, and frequency range of interest.

  • 31. Elnady, T.
    et al.
    Elsaadany, S.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Flow and Pressure Drop Calculation Using Two-Ports2011In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 133, no 4, p. 041016-Article in journal (Refereed)
    Abstract [en]

    Exhaust systems should be carefully designed for different applications. The main objective of an exhaust system is to reduce the engine noise. Maximum noise reduction is usually desired to the limit of a certain backpressure, which is set by the engine manufacturer in order not to deteriorate the engine efficiency. Therefore, a parallel calculation of the flow and pressure drop must be performed. The amount of flow flowing through each element will also affect its acoustic properties. Usually, acoustic and flow calculations are done separately on two different software. This paper describes a new technique that enables both calculations to be done using the same input data on the same platform. Acoustic calculations are usually performed in the frequency domain in the plane wave region using the two-port theory and then the acoustic pressure in the system is solved for using well-known algorithms to handle arbitrary connected two-ports. The stagnation pressure and volume flow can also be calculated using the same algorithm by deriving a flow two-port for each element using the stagnation pressure and the volume flow velocity as the state variables. The proposed theory is first discussed listing the flow matrices for common elements in exhaust elements, and then different systems are analyzed and compared with the measurements.

  • 32. Elnady, T.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    SIDLAB: New 1D sound propagation simulation software for complex duct networks2006In: 13th International Congress on Sound and Vibration 2006, 2006, p. 4262-4269Conference paper (Refereed)
    Abstract [en]

    Low frequency sound generation and propagation in duct and pipe systems is important in many applications. The examples range from ventilation systems to IC-engine exhaust and inlet systems. Plane wave two-port theory can be used to describe the sound transmission along the system. Based on a long experience of different applications, a new user-friendly software (SIDLAB) has been developed to meet today's engineering needs. The new software is MATLAB based and allows access to the source code. This gives the user a flexibility to do other calculations than those already defined and further post-process the data. SIDLAB includes typical two-port elements for many applications but also unique elements, e.g., for modelling devices for exhaust gas cleaning. It is also unique that the two-port elements are allowed to be active, i.e., contain sources. There is no limitation to the number of elements and they can be connected together in any arbitrary scheme. By introducing one-port elements, the network can handle several inlets and outlets. SIDLAB can simulate passive results, such as transmission loss and transfer matrices between arbitrary nodes (points) in the network. It can also simulate active results, such as pressure and sound power at each node in the network. In this paper an overview of the new software is presented together with an example of the analysis of a complex muffler.

  • 33. Elnady, T.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Allam, Sabry
    Modeling perforates in mufflers using two-ports2010In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 132, no 6, p. 061010-Article in journal (Refereed)
    Abstract [en]

    One of the main sources of noise of a vehicle is the engine where its noise is usually damped by means of acoustic mufflers A very common problem in the modeling of automotive mufflers is that of two flow ducts coupled through a perforate A new segmentation approach is developed here based on two port analysis techniques in order to model perforated pipes using general two port codes which are widely available Examples are given for simple muffler configurations and the convergence of the technique is investigated based on the number of segments used The results are compared with closed form solutions form the literature Finally an analysts of a complicated multi chamber perforated muffler system is presented The two port simulation results show good agreement with both the measurements and the simulations using the classical four port elements [DOI 10 1115/1 4001510]

  • 34. Elnady, Tamer
    et al.
    Elsaadany, Sara
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Investigation into modeling of multi-perforated mufflers2009Conference paper (Other academic)
    Abstract [en]

    There is a strong competition among automotive manufacturers to reduce the radiated noise levels. One main source is the engine where the main noise control strategy is by using efficient mufflers. Resistive mufflers are now widely used to attenuate IC-Engine noise due to its better performance over the reactive ones. Resistive damping can be achieved either by using absorbing material or perforates in the form of tubes or sheets. Perforates mufflers have an increased performance with flow when the acoustic impedance is increased by introducing flow through the perforate holes. On the other hand, perforates can deteriorate the engine performance, if badly designed, by increasing the flow back pressure. Modeling of perforated mufflers started in the seventies when simple geometries were used. There were two approaches to analyze two tubes connected with a perforate (i.e. four-port), segmentation and distributed. Both approaches were limited to a few specified geometries. Recently, the authors published a new technique based on the segmentation approach where four ports can be replaced by a number of two-ports so that it can be used in general two-port codes. This paper investigates the use of these techniques in modeling complex perforated muffler geometries. Fifteen different configurations were modeled and compared to measurements. There are some limitations to the use of these models in some configurations because of strong 3D effects that limits the validity of these models to almost half the plane wave region. These configurations are mainly the double plug flow muffler and the parallel tube mufflers.

  • 35.
    Elsaadany, Sara
    et al.
    Ain Shams Univeristy, Group for Advanced Resaerch in Dynamic Systems, Faculty of Engineering, Egypt.
    Elnady, Tamer
    Ain Shams Univeristy, Group for Advanced Resaerch in Dynamic Systems, Faculty of Engineering, Egypt.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Optimization of exhaust systems to meet the acoustic regulations and the enginespecifications2011Conference paper (Other academic)
    Abstract [en]

    Mufflers for internal combustion engines should be carefully designed. The main objective of a muffler is to reduce the engine noise while maintaining the back pressure below a certain limit. A specific target acoustic performance has to be met under space constraints and allowable engine back pressure limit. Usually, the insertion loss of the exhaust system is required to satisfy a certain target performance curve. The insertion loss is most appropriate to describe the exhaust system acoustic performance since it is dependent on the engine acoustic impedance, which varies with the engine loading and rotational speed. In this paper, a muffler optimization problem is formulated so that several shape parameters are optimized under some space constraints with flow. Any combination of linear space constraints can be imposed. The allowable engine back pressure is introduced as a non-linear constraint so that the optimum shape design will meet the engine back pressure specifications. The interior point optimization algorithm, which is available as a built-in MATLAB function "fmincon", is used in this paper. The formulated problem is applied to a real case study, where a truck exhau stsystem consists of a diesel engine, two mufflers, intermediate pipes, and a tailpipe. The first muffler is a typical EU-regulation compliant. The dimensions and location of the second muffler are to be optimized. A limit for the system back pressure is imposed by the engine manufacturer. An optimum design was investigated for different engine speeds and loadings. It was found that using the suggested formulation in this paper; one can obtain an applicable design of a muffler to meet both the acoustic regulations and the engine specifications.

  • 36.
    Elsaadany, Sara
    et al.
    Ain Shams University, Sound and Vibration Lab., Egypt.
    Elnady, Tamer
    Ain Shams University, Sound and Vibration Lab., Egypt.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Insight into exhaust systems optimization techniques2010Conference paper (Other academic)
    Abstract [en]

    Exhaust system mufflers should be carefully designed for different applications. The main objective of an exhaust system is to reduce the engine noise. Maximum acoustic performance is usually desired under the limit of space constraints. Therefore obtaining the muffler optimum design is very crucial. In this paper, the muffler optimization problem is formulated allowing getting the optimum muffler design through calculating the acoustic properties conjugated with the optimization technique using a function "fmincon" from the MATLAB optimization tool-box that finds the minimum of a constrained nonlinear multivariable function. There are several possibilities to evaluate the acoustic performance of a muffler such as the sound transmission loss, the insertion loss, and the acoustic pressure measured by a receiver outside the exhaust system opening. By selecting one of these design targets, the optimum design of a specific muffler configuration in the frequency range of interest can be obtained. In this paper, a shape optimization approach is presented for different mufflers configurations, and the results of transmission loss, insertion loss, and the outside acoustic pressure are compared against optimum designs from the literature obtained using different optimization methods as well as design targets.

  • 37. Fairbrother, R.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Glav, Ragnar
    Linear acoustic exhaust system simulation using source data from non linear simulation2005In: SAE technical paper series, ISSN 0148-7191Article in journal (Refereed)
    Abstract [en]

    Both linear (frequency domain) and non-linear (time domain) prediction codes are used for the simulation of duct acoustics in exhaust systems. Each approach has its own set of advantages and disadvantages. One disadvantage of the linear method is that information about the engine as an acoustic source is needed in order to calculate the insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. This source characterization data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These measurements are time consuming and expensive. However, this data can also be extracted from an existing 1-D non-linear CFD code describing the engine gas exchange process. The pressure and velocity predictions from two acoustic load cases can be used to determine the source strength and impedance at a particular location in the exhaust line. This has been done at a location downstream of the turbocharger in the exhaust system of a heavy diesel truck over a number of speeds and engine loads. This source data is then used in a linear simulation of the exhaust line to predict sound pressure levels at a free field microphone position. The predicted source data and sound output at the microphone position is validated against measured data. The results show that you can obtain reasonably accurate source data and approximate free field sound pressure level predictions using non linear simulation in a linear acoustic model of the exhaust system. This technique can be used to extend the use of linear acoustic simulations to models of the complete exhaust line with the characterized engine as a source and exhaust sound output as a result.

  • 38.
    Färm, Anna
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. Scania.
    Analysis of Acoustic Absorption with Extended Liner Reaction and Grazing Flow2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Acoustic absorbing liners are efficient and commonly used measures to reduce sound levels in many fields of application. The sound reducingperformance of the liners is dependent on the acoustic state, defined by e.g. the flow and sound field interacting with the liner. To enable liner optimization the impact of these factors on the liner performance must be predictable. Studies of the impact of these factors were performed with existing experimental, analytical and numerical methods at low Mach number flows and material used in truck engine compartments. The study showed significant impact of both flow and sound field onthe liner performance. The size of the impact of the flow depends on which of the existing methods and models that was used, implying theneed of complementary methods. A new numerical method to model the boundary layer effect was for this reason developed in this work. The method was shown to predict the impact of flow correctly compared to the Pridmore-Brown solution and the method was computationally efficient. The sound reducing performance of a liner exposed to complex sound field and grazing flow can be predicted using existing methods together with the new proposed method. Extra care has to be taken when bulk reacting liners are considered since additional complications compared to locally reacting surfaces occur in presence the of grazing flow.

  • 39.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    An Extended Transfer Matrix Approach to Model the Effect of Boundary Layers on Acoustic LiningsManuscript (preprint) (Other academic)
    Abstract [en]

    Sound absorbing materials exposed to grazing flow experience a change in the surface properties due to the boundary layer developed above the surface. The effect of this boundary layer is significant even for fairly low Mach numbers, and several attempts to find analytical models to describe this effect have previously been made. This paper proposes a numerical discretization method, based on the classic transfer matrix approach to model the boundary layer effect. The method includes the time averaged flow velocity gradients of the boundary layer, which is shown to be essential in order to obtain convergence to the correct solution. The method is found to predict the effect of the boundary layer on the surface properties correctly compared to previous numerical solutions. The proposed method is simple to implement, and benets from a fast convergence relative to other numerical methods.

  • 40.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows2013Conference paper (Other academic)
    Abstract [en]

    Sound absorbing linings are effective noise treatments in many applications in order to meet noise emission requirements. Stricter noise requirements set harder demands on the performance of the liners, why better prediction models of their performance have to be developed. As of today, several models to predict the sound reducing properties in the presence of flow exist and are shown to give diverging absorption properties for locally reacting liners exposed to high Mach number flows. The effect of flow on absorption properties is often seen as an issue that only needs to be addressed at high Mach number flows. In this paper, the existing models are applied to bulk reacting liners exposed to low Mach number flows and the resulting absorption coefficients are compared. Predictions of absorption coefficients clearly show that the effect of flow needs to be considered also at low Mach number flows and that the difference between the prediction models is indeed significant at low Mach number flows. This shows the importance in choosing the correct model for a specific application in order to avoid introducing erroneous prediction on the effect of flow. This study thus gives well-grounded evidence of the importance to include flow effects in modeling of sound absorptive linings even at low Mach number flows.

  • 41.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dazel, Olivier
    University of Maine, Acoustical Labratory, France.
    Prediction of acoustic surface impedance of bulk reacting lining with grazing flow2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, International Institute of Acoustics and Vibrations , 2014, p. 2332-2339Conference paper (Other academic)
    Abstract [en]

    A transfer matrix methodology to determine the acoustic properties of multi-layered absorbers in different environments is proposed in this paper. The methodology allows inclusion of grazing flow and the boundary layer effects on the surface properties, avoiding the need of several complementary methods to obtain the surface properties of a sound reducing material in a specific environment. The predicted surface properties are given as a function of angle of sound incidence, allowing for arbitrary sound fields to be simulated. This is a useful tool in for example automotive applications such as engine bays where multi-layered bulk reacting sound absorbing materials are exposed to flow and complex sound fields. Correct prediction of the acoustic performance of absorbing material where flow is present enables optimization of the noise reducing components for which conflicting requirements such as weight and space constraints are present as well.

  • 42.
    Färm, Anna
    et al.
    Scania CV AB, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Glav, Regnar
    Scania CV AB, Sweden.
    On sound absorbing characteristics and suitable measurement methods2012In: SAE Technical Paper 2012-01-1534, 2012, Society of Automotive Engineers, 2012Conference paper (Refereed)
    Abstract [en]

    Noise encapsulations are widely used in automotive industry to enclose noise sources, such as e.g. the engine or the gearbox, to reduce externally radiated noise. The sound absorption factor of the material on the inside of the noise encapsulation is obviously vital for the sound attenuation. This parameter is in most cases determined experimentally for which there are several methods. The results received from the various methods may vary as different acoustic states are examined and thus influence the choice of method. The absorption factor is crucial since it is used in specifications to material manufacturers as well as being an input parameter in modeling the performance of the noise shield e.g. during a pass-by noise test.

    In this paper, two standardized measurement methods along with a third, non-standardized method, are applied to determine the properties of an absorbing material used in a commercial noise encapsulation. The methods are based on normal-, random- and oblique incident sound waves. The first and the last methods are based on measuring the acoustic impedance from which the absorption can be calculated while the random incidence method measures the absorption directly. The results retrieved from the three methods are compared and discussed in the light of the differences between them. This paper clarifies the differences and gives a practical guidance for the choice of measurement method and the use of the different absorption factors in modeling.

  • 43.
    Färm, Anna
    et al.
    Centre for ECO Vehicle Design, Scania CV, Södertälje, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Glav, Ragnar
    Scania CV, Södertälje, Sweden.
    On internal mean flow in porous absorbers and its effect on attenuation properties2013In: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, Vol. 19, p. 1-6Conference paper (Other academic)
    Abstract [en]

    In vehicle applications, absorbing materials are often used to attenuate sound. In, for example, exhaust systems and on noise encapsulations, the absorber is exposed to flow. This creates a boundary layer above the absorber, which affects the impedance of the surface, and hence alters the absorption properties. In addition to this effect, the flow itself may enter the absorbent material due to high pressure and forced flow paths. An investigation of the effects that internal flow in the absorber imposes on the acoustic properties is presented. One way to describe the effect is by a change in flow resistivity. The effect is investigated for typical absorbers used in noise encapsulations for trucks. The Transfer Matrix Method is applied to calculate the resulting absorption coefficient for an absorber with changed flow resistivity due to internal flow. The possibility to model the changed properties of the absorber with internal mean flow by means of Biot theory is also explored, together with a discussion on suitable experimental methods to verify and further investigate the effects.

  • 44.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. Acoustics department, Scania CV AB, Södertälje, Sweden.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Acoustics department, Scania CV AB, Södertälje, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    On variation of absorption factor due to measurement method and correction factors for conversion between methods2012In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, Volume 11, 2012, Institute of noise control engineering , 2012, p. 9343-9350Conference paper (Other academic)
    Abstract [en]

    Sound absorbing materials are used in many applications to reduce sound, and their soundabsorbing characteristics are most often determined experimentally since theoreticaldetermination is difficult. Sound absorption factors are used in material specifications aswell as input to numerical simulations.Several methods for experimental determination of the absorption factor exist, two of themstandardized and frequently used. It is commonly known that the absorption factorobtained by these two methods differs as different sound fields are prescribed by thestandards. However, the size of the differences has not been so well described. Due to thisdifference, the choice of method is critical in order to avoid errors in simulations andspecifications of material properties.Experimental determination of absorption factors for three commonly used absorbers wasperformed, resulting in significant differences between the two methods. Correction factorsto compensate the absorption factor determined at one acoustic state and used in anotherare given. Theory verifying the differences is also presented.

  • 45.
    Glav, R
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    The point-matching method on dissipative silencers of arbitrary cross-section1996In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 189, no 1, p. 123-135Article in journal (Refereed)
  • 46.
    Glav, Ragnar
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Exhaust and Intake Noise and Acoustical Design of Mufflers2008In: Handbook of Noise and Vibration Control / [ed] Malcolm J. Crocker, John Wiley & Sons, 2008, p. 1034-1053Chapter in book (Refereed)
    Abstract [en]

    A muffler or silencer is a device used in a flow duct to prevent sound from reaching the openings of the duct and radiating as far-field sound. Reactive silencers do this by reflecting sound back towards the source while absorptive silencers attenuate sound using absorbing material. They are necessary components in the design of any exhaust or intake system for internal combustion (IC) engines. No car or truck can pass the standard noise tests required by legislation or compete on the market without them. There are three basic requirements for a modern exhaust systems; compact outer geometry, sufficient attenuation and low pressure drop.

     

    The aim of this chapter is to discuss acoustical design and analysis of IC-engine exhaust and intake systems. The specific problems of modern intake systems made from plastic material with non-rigid walls are not discussed because not much has been published on this subject. The theory and techniques presented can be used also for other applications such as compressors and pumps and to some extent also for air-conditioning and ventilation systems.

  • 47.
    Glav, Ragnar
    et al.
    Scania AB, Sweden.
    Färm, Anna
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Analysis of a cylindrical micro-perforated resistive silencer2013In: 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, p. 5867-5876Conference paper (Refereed)
    Abstract [en]

    This paper presents an analytical wave decomposition model for predicting the transmission loss a cylindrical silencer with both annular and baffled micro-perforated screens. Numerical simulation shows the fundamental characteristics as well as the potential to achieve large attenuation using micro-perforations. The numerical model is verified by measurements using the 2-microphone technique and shown to be a useful tool in practical design. Clear from the analysis is the sensitivity of the micro-perforated silencer to changes in both porosity and overall layout.

  • 48.
    Guo, Ying
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Allam, Sabry
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Micro-Perforated Plates for Vehicle Applications2008In: Proceedings of the 2008 Congress and exposition of noise control engineering, Inter-Noise 2008, 26-29 Oct, Shanghai, China, 2008Conference paper (Refereed)
  • 49.
    Guo, Ying
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dolinar, Andreas
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Allam, Sabry
    Experimental Investigation of Acoustic Properties of Mufflers with Perforated Pipes2007In: 19th International Congress on Acoustics Madrid, Spain, September 2007, 2007Conference paper (Refereed)
  • 50.
    Hedekäll, Johan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    High frequency vibrations in chipping hammers2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Percussive tools such as chipping hammers, riveting hammers and concrete breakers produce shock-type (impact) vibrations with large amount of vibration energy in the high frequency region (kHz). Reported injuries from shock-type and high frequency vibrations are higher  occurrence of vascular disorders, myelin disruption, edema and reduced motor performance.

    An Atlas Copco Tools customer has reported an increase of VWF (vibration induced white finger) during the last decade and the chipping hammers have been identified as the main cause. A mean of 1.8 workers/year has been injured with VWF and the cost of one injured worker has been estimate to 0.5 million SEK. One way to eliminate the injuries could be to replace the tools from Atlas Copco with better tools from another manufacturer.

    A protective handle was designed for the chipping hammers by Atlas Copco, to prevent operators from holding directly on the vibrating parts. However, the protective handle was not vibration isolated and a follow up project, this thesis, was started to redesign and vibration isolate the handle. An isolated protective handle with two rubber bushings was finally developed from theory of vibration isolation together with a subjective evaluation by experienced personnel and with low and high frequency vibration measurements.

    The final protective handle significantly reduced both the harmful low frequency vibrations (measured according to ISO 5349) and the potentially harmful high frequency vibrations (not measured according to any ISO standard), compared to the non-isolated original handle  developed by Atlas Copco.

12 1 - 50 of 84
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