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  • 301.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Acoustic properties of perforates under high level multi-tone excitation2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. Compared to previously published results the present investigation concentrates on the effect of multiple harmonics. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied.

  • 302.
    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).
    APPLICATION OF NONLINEAR SYSTEM IDENTIFICATION TECHNIQUES FOR DETERMINATION OF ACOUSTIC PROPERTIES OF IN-DUCT COMPONENTS2015Inngår 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]

    This paper discusses the use of nonlinear system identification techniques for determination of linear and non-linear acoustic properties of in-duct components. Examples include perforates, orifices and acoustic liners. These types of components can for instance be found in aircraft engines, IC-engine exhaust and intake systems and ventilation ducts. Multiple input single output nonlinear system identification techniques are revisited and applied to the problem of nonlinear acoustic characterization of these components. Bi-linear signal analysis techniques are also discussed as well as empirical mode decomposition and Hilbert transform techniques applicable for non-stationary and nonlinear problems. Methods for studying nonlinear harmonic interaction effects, for perforates, using single tone excitation has been studied in previous work by the author. These techniques typically require measurements with a number of different acoustic loads. It would be more attractive to directly be able to extract the nonlinear acoustic properties from a more limited set of experiments using either random or periodic excitation. The idea of treating a nonlinear path as a separate non-linear input after which system identification is performed as for a linear two input one output system are revisited here in an attempt to analyze why unsatisfactory results were obtained in a previous study.

  • 303.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Experimental investigation of harmonic interaction effects for perforates2005Inngår i: Collection of Technical Papers: 11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, 2005, Vol. 2, s. 1236-1242Konferansepaper (Fagfellevurdert)
    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.

  • 304.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation2011Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 130, nr 5, s. 2639-2647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristic. The methods developed are intended both 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 and for samples accessible from both sides such as perforates or other top sheets. When harmonic sound waves are incident on the sample nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea is that these sources can be characterized using linear system identification techniques similar to one-port or two-port techniques which are traditionally used for obtaining source data for in-duct sources such as IC-engines or fans. The starting point will be so called polyharmonic distortion modeling which is used for characterization of nonlinear properties of microwave systems. It will be shown how acoustic source data models can be expressed using this theory. Source models of different complexity are developed and experimentally tested. The results of the experimental tests show that these techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 305.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    In-duct source characterization for multiple sources2009Inngår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, s. 2664-2671Konferansepaper (Fagfellevurdert)
    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.

  • 306.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    International Journal of Aeroacoustics, volume 6, number 12007Collection/Antologi (Fagfellevurdert)
    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.

  • 307.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Multi-port techniques for acoustic characterisation of non-linear in-duct discontinuities2009Inngår i: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009Konferansepaper (Fagfellevurdert)
    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. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested. These new techniques take non-linear energy transfer between sound field harmonics into account.

  • 308.
    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).
    Nonlinear source characterisation techniques for IC-engines2012Inngår i: 19th International Congress on Sound and Vibration 2012, ICSV 2012, 2012, s. 2442-2449Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A source characterization model for IC-engines, which can take weakly nonlinear source properties into account, is developed in the paper. It is based on so called polyharmonic distortion modeling, used for nonlinear characterization of microwave systems. Comparisons are made with the results from linear source models and another previously published weakly nonlinear source model. The results show that the new nonlinear impedance matrix model gives improvements in the prediction of sound pressure levels in the exhaust system.

  • 309.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Vibrationsövervakning.
    Non-linear system identification techniques for determination of the acoustic properties of perforates2015Inngår i: 21st AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners. Multiple input single output nonlinear system identification techniques are revisited and applied to the problem of nonlinear acoustic characterisation of perforates. Bi-linear signal analysis techniques are also tested as well as Hilbert transform techniques applicable for non-stationary and nonlinear problems. It is shown that random excitation nonlinear system identification techniques have the potential of identifying and characterising non-linear acoustic properties of these types of samples.

  • 310.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    On impedance measurements for samples with non-linear acoustic properties2008Inngår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, BC, 2008Konferansepaper (Fagfellevurdert)
    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.

  • 311.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties2012Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, nr 13, s. 3050-3067Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 312.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Polyharmonic distortion modelling applied to acoustic characterisation of peforates2011Inngår i: 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference), 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the possibility to apply polyharmonic distortion modelling, used for nonlinear characterisation of microwave systems, to acoustic characterisation of samples with non-linear properties such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. In some previous papers multi-port techniques using sinusoidal excitation for characterization of samples with non-linear properties were developed and experimentally tested. These techniques aimed at taking non-linear energy transfer between sound field harmonics into account. Essentially linear system identification theory was however used assuming that superposition applies and that the functions studied are analytical. Polyharmonic distortion modelling does not assume that the function relating waves incident and reflected or transmitted is analytic nor does it assume application of normal superposition. This technique is tested on experimental data obtained from measurements on a perforate mounted in a duct. The similarity to the previously developed nonlinear scattering matrix techniques is demonstrated. It is shown how the results obtained can be used to analyse nonlinear energy transfer to higher harmonics. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

  • 313.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Recent Advances In  IC-engine acoustic source Characterisation2007Inngår i: 14th International Congress on Sound and Vibration (ICSV14), 2007Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper summarizes work performed at KTH over the years on source characterization for IC-engine exhaust and intake systems. An overview is made of recent advances in experimental and simulation methods for determination of acoustic source data. These include a source model which can consider weakly non-linear sources and application of 1-D CFD codes for extracting source data. Examples are presented for both exhaust and intake systems and for different types of engines. The results show that reasonably accurate results can be obtained using 1-D CFD codes to extract acoustic source data and that the newly developed non-linear multi-load technique has got advantages over the traditional two-load technique for determining source data from experiments.

  • 314.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Single tone excitation techniques for determination of non-linear acoustic properties of perforates2010Inngår i: Proceedings of the International Conference on Noise and Vibration Engineering, ISMA 2010, 2010, s. 597-609Konferansepaper (Fagfellevurdert)
    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.

  • 315.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Study of nonlinear energy transfer for perforated wall treatment using acoustic source characterisation techniques2011Inngår i: 18th International Conference on Sound and Vibration (ICSV18), 2011Konferansepaper (Annet vitenskapelig)
    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.

  • 316.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The effect of high level multi-tone excitation on the acoustic properties of perforates and liner samples2012Inngår i: 18th AIAA/CEAS Aeroacoustics Conf. (33rd AIAA Aeroacoustics Conf.), American Institute of Aeronautics and Astronautics, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates and liner samples. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. First a quasi-stationary model for the acoustic properties of the perforate is discussed and the results are compared to experimental data. The effect of the combination of frequency components in the excitation signal is studied to find out if it matters if we are using tones which are harmonically related or not. The effect the phase of the frequency components is studied using both the model and experimental data. It is also discussed if a parameter controlling the impedance can be found for an arbitrary combination of tones with different frequencies.

  • 317.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    The effect of speed variation on in-duct source data determination2014Inngår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, s. 2395-2401Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental acoustic source characterization is used for IC-engines and fluid machines connected to duct or pipe systems. Information about the engine as an acoustic source is needed to calculate insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is often the linear time invariant 1 -port model. The acoustic source data is obtained from experimental tests or from 1 -D CFD codes describing the engine gas exchange process. Multi-load methods and especially the two-load method are most commonly used to extract the source data. The IC-engine is a high level acoustic source and in most cases not completely linear. The real part of the measured source impedance sometimes has negative values which is un-physical. This effect has been attributed to non-linearity and source time variation. Another possible explanation could be speed variation giving measurement errors especially for higher harmonics. In the present paper this effect is studied by re-visiting source data experiments for IC-engine exhausts and comparing the outcome of different methods for extracting the amplitude and phase of the pressure in terms of frequency components or engine orders.

  • 318.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Two-Port Techniques For Characterisation Of Non-Linear In-Duct Sources2008Inngår i: 15th International Congress on Sound and Vibration (ICSV15), 2008Konferansepaper (Annet vitenskapelig)
    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. 

  • 319.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Two-sided multi-port techniques for characterisation of in-duct samples with non-linear acoustic properties2013Inngår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 99, nr 3, s. 359-378Artikkel i tidsskrift (Fagfellevurdert)
    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 experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 320.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Allam, Sabry
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Experimental Techniques for Aeroacoustics in Low Mach Number Confined Flows: Keynote Paper2011Inngår i: Proceedings of the International Conference on Mechanical Engineering 2011(ICME2011) 18-20 December 2011, Dhaka, Bangladesh, ICME , 2011Konferansepaper (Annet vitenskapelig)
    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.

  • 321.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Aslan, Johan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Yousif, Michel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A study of annoyance caused by ground based activities at Bromma airport2010Inngår i: 17th International Congress on Sound and Vibration (ICSV17), 2010Konferansepaper (Annet vitenskapelig)
    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.

  • 322.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Spillere, A. M.
    Effect of flow direction on acoustic liner impedance measurement results2016Inngår i: ICSV 2016 - 23rd International Congress on Sound and Vibration: From Ancient to Modern Acoustics, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing effort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs for determination of liner impedance including the effect of mean flow use plane wave excitation on the upstream side of the liner. Some studies has compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature to see if the trend of obtaining different results for upstream and downstream excitation is persistent.

  • 323.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Spillere, A. M. N.
    Serrano, P. G.
    Comparison of the effect of flow direction on liner impedance using different measurement methods2017Inngår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There is an ongoing scientific discussion about the effect of flow on experimental techniques for determination of acoustic liner impedance. This paper contributes to this continuing effort to gain confidence in results obtained under different acoustical and flow excitation configurations. A majority of the test rigs for determination of liner impedance including the effect of mean flow use plane wave excitation on the upstream side of the liner, but some studies have compared the results for downstream acoustic excitation. Especially for the so-called inverse impedance eduction techniques, it has been reported that different flow directions compared to the acoustic excitation can provide different educed impedances. It is still an open question if this results are due to the application of the Ingard-Myers boundary condition, to other errors or flaws in the measurements or a characteristic of the liner itself. This paper revisit some previous published results and compares the result obtained by means of inverse impedance eduction techniques, which in general adopt the Ingard-Myers boundary condition, and in-situ impedance measurements, which do not require the definition of a boundary condition. It is seen that discrepancies between downstream and upstream measurement can be observed in both approaches, and a discussion on such behavior is presented.

  • 324.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Aeroacoustics research in Europe: The CEAS-ASC report on 2012 highlights2013Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 332, nr 25, s. 6617-6636Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.

  • 325.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Eslami, Armin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Determination of non-linear acoustic properties of perforates using single tone excitation2010Inngår i: 17th International Congress on Sound and Vibration (ICSV17), 2010Konferansepaper (Annet vitenskapelig)
    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.

  • 326.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Fritzell, Julius
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A study of high level tonal and broadband random excitation for acoustic liners2017Inngår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the effect of high level broad band and tonal acoustic excitation on the acoustic properties of perforates. It is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. In previous studies multiple tone and high acoustic excitation levels were studied. Both normal incidence impedance tube measurements and liners placed in a grazing incidence configuration were considered. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. The combination of tones as well as the relative phase between frequency components has also been shown to influence the result. There is usually also a broadband random level excitation in combination with the harmonic tonal excitation. The effect of this combination on the acoustic properties of a perforate has been studied.

  • 327.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Guo, Ying
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Tözün, Hüseyin Bora
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Experimental investigation of nonlinear acoustic properties for perforates2006Inngår i: Collection of Technical Papers: 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 2006, Vol. 1, s. 67-74Konferansepaper (Fagfellevurdert)
    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.

  • 328.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Guo, Ying
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Tözün, Hüseyin Bora
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Investigation of Nonlinear Acoustic properties for Perforates2006Inngår i: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Konferansepaper (Annet vitenskapelig)
    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 has been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.

  • 329.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Khodashenas, Niloofar Sayyad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Experimental study of nonlinear acoustic properties of perforates using band-limited random excitation information2018Inngår i: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, Vol. 3, s. 1818-1825Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Perforates are used for noise control in automotive mufflers and aircraft engine liners as well as for other vehicles and machines. Their acoustic properties and noise reduction are known to depend on the mean flow field and other parameters such as temperature and acoustic excitation level. It is therefore of interest to understand how the properties of perforates varies with the level of acoustic excitation. This paper gives an overview of high level nonlinear effects on the acoustic properties of perforates. It includes semi-empirical models as well as experimental studies. Methods for studying nonlinear effects and harmonic interaction effects, for perforates, using single tone excitation and Poly-harmonic distortion models or nonlinear scattering matrices are discussed. These techniques typically require measurements with a number of different acoustic loads. It would be more attractive to directly be able to extract the nonlinear acoustic properties from a more limited set of experiments using either random or periodic excitation. Multi input - single output techniques for nonlinear system identification using broadband random excitation has been tried with limited success. One reason is the mixing of the sound pressure signal incident from the acoustic source with the sound pressure transferred to higher frequencies by nonlinear effects at the perforate sample. The present paper includes an attempt to combine band-limited broadband excitation with Poly-harmonic distortion models or nonlinear scattering matrices describing the nonlinear transfer of energy to higher frequencies.

  • 330.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    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 systems2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 2231-2238Konferansepaper (Fagfellevurdert)
    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.

  • 331.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Zhou, L.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing e ort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs use plane wave excitation on the upstream side of the liner for determination of liner impedance including the effect of mean flow. Some studies have compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature as well as some new data to see if the trend of obtaining di erent results for upstream and downstream excitation is persistent. The Ingard-Myers boundary condition and alternative formulations published in the literature are discussed. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

  • 332.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation2012Inngår i: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise): FIV2012, Dublin, Ireland, 3-6 July 2012 FLOW-INDUCED VIBRATION, 2012, s. 187-193Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper experimentally investigates the acousticproperties of an orifice with bias flow under medium andhigh sound level excitation. The test included no bias flowand two bias speeds for three different frequencies. Experimentalresults are compared and discussed with theory.It is shown that bias flow makes the acoustic propertiesmuch more complex compared theory and with theno bias flow case, especially when velocity ratio betweenacoustic particle velocity and mean flow velocity is nearunity.

  • 333.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Zhou, Lin
    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).
    An experimental study of the effect of flow and high level acoustic excitation on the acoustic properties of perforates and orifices2013Inngår i: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, s. 2545-2552Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Perforates are for instance used in mufflers for automotive applications and in acoustic liners for aircraft engines. In these applications they are often exposed to high level acoustic excitation in combination with grazing or bias flow. The paper is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow as well as on a study of an orifice with bias flow under medium and high sound level excitation. The effect of grazing flow is discussed based on data from the literature. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modeling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied. The bias flow tests included different flow speeds for different frequencies. The level of acoustic excitation is varied from much smaller to larger than the mean flow velocity. It is shown that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.

  • 334.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing e ort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs use plane wave excitation on the upstream side of the liner for determination of liner impedance including the effect of mean flow. Some studies have compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature as well as some new data to see if the trend of obtaining di erent results for upstream and downstream excitation is persistent. The Ingard-Myers boundary condition and alternative formulations published in the literature are discussed.

  • 335. Boelens, O. J.
    et al.
    Badcock, K. J.
    Görtz, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Morton, S.
    Fritz, W.
    Karman, S. L., Jr.
    Michal, T.
    Lamar, J. E.
    F-16XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International2009Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, nr 2, s. 369-376Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamics Project flight database. A major part of this work involved the generation of high-quality computational grids. Before the grid generation, an airtight geometry of the F-16XL, aircraft was generated by a cooperation of the Cranked-Arrow Wing Aerodynamics Project International partners. Based on this geometry description, both structured and unstructured grids have been generated. The baseline structured (multiblock) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory. Although the algorithms used by the National Aerospace Laboratory had become available just before the Cranked-Arrow Wing Aerodynamics Project International and thus only a limited experience with their application to such a complex configuration had been gained, a grid of good quality was generated well within four weeks. This time compared favorably with that required to produce the unstructured grids in the Cranked-Arrow Wing Aerodynamics Project International. The baseline all-tetrahedral and hybrid unstructured grids have been generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, trimmed unstructured grids have been generated at the European Aeronautic Defence and Space Company's Military Air Systems, University of Tennessee at Chattanooga SimCenter, Boeing Phantom Works, Royal Institute of Technology, and the Swedish Defence Research Agency. All grids generated within the framework of the Cranked-Arrow Wing Aerodynamics Project International will be discussed in the paper. Both results obtained on the structured grids and the unstructured grids showed a significant improvement in agreement with flight-test data in comparison with those obtained on the structured multiblock grid used during the Cranked-Arrow Wing Aerodynamics Project.

  • 336. Boelens, O. J.
    et al.
    Görtz, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Morton, S.
    Fritz, W.
    Lamar, J. E.
    Description of the F-16XL geometry and computational grids used in CAWAPI2007Inngår i: Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting, 2007, s. 5866-5878Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of the Cranked-Arrow Wing Aerodynamics Project International (CAWAPI) was to allow a comprehensive validation of Computational Fluid Dynamics methods against the CAWAP flight database. A major part of this work involved the generation of high-quality computational grids. Prior to the grid generation an IGES file containing the air tight geometry of the F-16XL aircraft was generated by a cooperation of some of the CAWAPI partners. Based on this geometry description both structured and unstructured grids have been generated. The baseline structured (multi-block) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory NLR. The baseline all-tetrahedral and hybrid unstructured grids were generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, additional unstructured grids were generated at EADS-MAS, the UTSimCenter, and Boeing Phantom Works. All the grids generated within the framework of CAWAPI will be discussed.

  • 337. Boere, Stijn
    et al.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Kuijpers, Ard
    Nijmeijer, Henk
    Tyre/road interaction model for the prediction of road texture influence on rolling resistance2014Inngår i: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 65, nr 2-3, s. 202-221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel modelling approach to predict the influence of road texture on the rolling resistance of car tyres is presented where the large static tyre deformations and the small texture induced tyre vibrations are treated separately. The energy dissipation due to the large continuous cyclic deformation of the tyre cross section for a treadless tyre subject to nominal load on a smooth road is determined in a non-linear steady-state rolling analysis on an FEM tyre model. The additional energy dissipation resulting from the con tact forces and tyre vibrations due to the combined effect of the tread profile and the road texture, are determined based on a modal representation of the deformed tyre. The predicted rolling resistance coefficients are compared to experimental data. Although an offset in the absolute rolling resistance levels can be observed, the model predicts the correct trend regarding the increase of rolling resistance with increasing texture depth.

  • 338.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    An analysis of the acoustic energy in a flow duct with a vortex sheet2009Inngår i: MATHEMATICAL MODELING OF WAVE PHENOMENA / [ed] Nilsson B; Fishman L; Karlsson A; Nordebo S, 2009, Vol. 1106, s. 130-139Konferansepaper (Fagfellevurdert)
    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.

  • 339.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow effects on the acoustic end correction of a sudden in-duct area expansion2009Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 126, nr 3, s. 995-1004Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For scattering of plane waves at a sudden area expansion in a duct, the presence of flow may significantly alter the reactive properties. This paper studies the influence of a mean flow field and unstable separated flow on the reactive properties of the expansion, formulated as an end correction. Theoretical and experimental results show that the expansion end correction is significantly affected by the flow and hydrodynamic waves excited at the edge of the expansion. The effects are different in three regions where the Strouhal number is small, of order 1, and large. The influence is most significant at Strouhal numbers of the order 1, with specific limiting values for large and small Strouhal numbers, respectively. In the analytic model, an important feature is the shear layer at the edge modeled as a vortex sheet with the unsteady Kutta condition applied at the edge. The influence of Mach number, Helmholtz number, and area expansion ratio is studied, and a quasistationary, small Strouhal number, approximation yields an expression for the end correction. Further, the influence of edge condition is explored, emphasizing the importance of interaction between sound and unsteady vorticity shedding at the edge of the area expansion.

  • 340.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Low frequency sound absorption at sharp edges in flow ducts2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 2390-2397Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow-acoustic interaction. The vortex sheet model is an analytical linear acoustic model, where 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, we study plane wave propagation at such an area expansion. The flow-acoustic interaction is described in terms of energy flow. A classification of modes as "hydrodynamic" and "acoustic" is used to separate the acoustic energy from the part of the energy arising from the steady flow field. Theoretical results are presented together with experimental data. The energy distribution and dissipation of acoustic energy is studied schematically, indicating the effects of the flow acoustic interaction due to the area expansion and the sharp edge.

  • 341.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Parameter dependence of flow acoustic interaction2006Inngår i: Mathematical Modeling of Wave Phenomena / [ed] Nilsson, B; Fishman, L, MELVILLE: AMER INST PHYSICS , 2006, Vol. 834, s. 100-108Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The possibility to predict flow acoustic coupling at a sharp edge of an area expansion in a flow duct is explored, starting from the analytical model proposed by Nilsson and Boij. In the model, the vortex shedding is treated as infinitely thin, causing an instability for all frequencies. For small and large values of the Strouhal number, the acoustic field is well defined and can be treated separately from the remaining flow field. For intermediate Strouhal numbers, this classification into acoustic and non-acoustic waves is more complex. In particular, a hydrodynamic wave and higher order, non-propagating acoustic waves are changing properties. The possibility to use the amount of deviation from the asymptotic behaviour as a measure of the strength of the interaction at the edge is explored. It is shown that the interaction is strongly dependent on the area ratio at the duct expansion. Further studies would aim to a more elaborate investigation of the implications of the wave number parameter dependence. The objective would be to better predict the circumstances for strong interaction, in order to design less noisy ventilation and exhaust systems and to enhance dissipation effects.

  • 342.
    Boij, Susann
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cinar, ÖY.
    Gebze Institute of Technology, Turkey.
    Cinar, G.
    Gebze Institute of Technology, Turkey.
    Nilsson, B.
    Linneaus University, School of Computer Science, Physics and Mathematics, Sweden.
    Scattering of sound waves at an area expansion in a cylindrical flow duct2013Inngår i: Proceedings of Meetings on Acoustics: Volume 19, Issue 1, June 2013, Acoustical Society of America (ASA), 2013, s. 030016-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sound propagation in pipes and ducts with flow, like ventilation ducts and exhaust pipes, is influenced by flow separation and vortex production at sharp edges along the ducts, such as at bends and area expansions. Shear layers form at the separation points, and such layers are unstable to low frequency acoustic disturbances. An analytical model, aiming at physical insight into this interaction is presented. Results in the plane wave region for the so called scattering matrix for a sudden area expansion with flow in cylindrical pipes are compared with experimental values. Both the magnitude and the phase, in the form of an end correction, is presented. The model is also compared to a 2 dimensional model, in order to evaluate the anticipated increased accuracy of the 3 dimensional modeling. The scattering coefficients are strongly dependent on the flow speed, which is up to a Mach number of 0.5. It is observed that for low frequencies, the interaction is dominated by the dynamics of an unstable shear layer downstream of the edges. For higher frequencies, the wave propagation is mainly affected by convective effects. Differences in properties for the 2D and the 3D case are also explored.

  • 343.
    Boij, Susann
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Nilsson, B.
    Växjö University, School of Mathematics and Systems Engineering, Sweden.
    Scattering and absorption of sound at flow duct expansions2006Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 289, nr 3, s. 577-594Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The scattering of plane acoustic waves at area expansions in flow ducts is analysed using the vortex sheet model where the flow at the expansion is modelled as a jet, with a vortex sheet emanating from the edge. Of particular interest is the influence of the flow field on acoustic scattering and absorption. First, it is demonstrated that the stability properties of the shear layer can be simulated by modifying the edge condition within the vortex sheet model. To this end the accuracy for the region where the shear layer is changing from unstable to stable is improved by introducing a gradually relaxed Kutta edge condition with empirically derived coefficients. For low Strouhal numbers the vortex sheet model applies and for higher Strouhal numbers the two models converge. Second, it is demonstrated that the acoustic transmission through the jet expansion region can be determined by neglecting the scattering there. Incorporating this assumption, the vortex sheet model reproduces well the experimental results on transmission and absorption for an area expansion. This result supports the assumption that the main part of the scattering occurs at the area expansion at least for the low-frequency range. Furthermore, the influence of the flow field is particularly strong for small Strouhal numbers.

  • 344.
    Boij, Susann
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Nilsson, B.
    Växjö University, International Centre of Mathematical Modelling School of Mathematics and Systems Engineering, Sweden.
    Sound in flow ducts with sharp edges2007Inngår i: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Important transmission paths for the noise produced by fans, engines and other machinery are the connecting ducts used for transport of gases. Hence, reliable methods for calculating the acoustic attenuation in such systems are of great interest. In the presence of sharp edges strong interaction between sound and flow may occur even at low Mach numbers, which should be accounted for. The interaction has been successfully described using the vortex sheet model with an unexpanded and unstable jet. The current paper deals with the generalization to stable jets. By using the so-called Building Block Method, rather complex silencers can be modelled from the results of two canonical problems: the scattering at the trailing and leading bifurcations, respectively. The strong flowacoustic interaction occurs at the trailing edge only. Results are presented here for the bifurcation and the sudden area change at the trailing edge. The flow in the large part of the duct downstream and upstream of an area change is modelled in two regions where the acoustically thin shear layer is described by a newly proposed set of coupling conditions. We use a simple model with physically realistic stability properties for acoustically thin layers allowing for a hydrodynamically thick shear layer. In fact, the dynamic properties of the shear layer are changed continuously with the shear layer Strouhal number s from the unstable at vanishing s to a stable layer at high s. The transfer Strouhal number marks the border between the unstable and stable region. Like the vortex sheet model, two coupling conditions relate the fields on each side of the sheet, one of them being continuity of pressure. The second coupling condition means continuity of a variable ranging from displacement, similar to the vortex sheet model, at vanishing s via velocity to pressure gradient at infinite s. The used shear layer model is uniformly valid for all s and allows a straightforward generalization of a scattering theory for unstable shear layers, i.e. for small s. Analytic as well as numerical results for the acoustic scattering are presented.

  • 345.
    Boij, Susann
    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.
    Pieters, R.
    Eindhoven University of Technology, Department of Applied Physics, Netherlands.
    Reflection properties of a flow pipe with a small angle diffuser outlet2010Inngår i: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 1, 2010, s. 706-712Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The reflection of plane acoustic waves is studied for an open pipe termination where the outlet section about 10 cm long is a diffuser with a small angle. Diffuser angles up to 6o with a sharp outlet edge are considered both without and with a mean flow. The experiments are performed for Helmholtz numbers, He, based on the pipe diameter, up to 1.0 and mean flow Mach numbers, M, up to 0.25. A multi-microphone method is used for accurate measurements of the acoustic fields inside the pipe. With no mean flow, the reflection coefficient results are compared with the theories for thin walls by Levine and Schwinger [1] and for the end correction and thick walls by Ando [2], respectively. The data for the magnitude of the reflection coefficient for different pipe end geometries show that in the low frequency regime it is the outlet radius that determines the magnitude of the energy reflection coefficient. The same collapse in the data is not obtained for the end correction which is strongly affected by the pipe end geometry. Experimental results of the reflection coefficient in the presence of a mean flow show a similar behaviour as without flow. However, it is the Strouhal number of the outlet that governs the losses, i.e., radiation and flow losses. For a region of small Strouhal numbers, the reflection is larger than one, as predicted for straight pipes, [3, 4]. An increased diffuser angle and rounded edges both increase the reflection at the pipe termination in a critical range of Strouhal numbers, which indicates that the reflection coefficient is strongly dependent on the shape, half angle, and edge curvature of the pipe end in this region.

  • 346.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Influence of turbulence and wind speed profiles on vegetation noiseManuskript (Annet vitenskapelig)
  • 347.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Masking of wind turbine sound by ambient noise2006Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The main objective of this work was to gain an increasing understanding of the properties of vegetation noise and also to the relative ratios of different natural ambient noises to mask wind turbine sound.

    A discrete vegetation noise model was developed and compared to an earlier model showing improved estimations, especially at frequencies below 0.5 kHz. Field measurements of sound from deleafed trees are compared to a deleafed tree model with satisfactory agreement. A wind turbulence model (Sandia method) was coupled to the discrete model and thereby time series of fluctuating vegetation noise can be computed. Several measurements including higher wind speeds than reported in earlier literature were compared to predictions of fluctuating vegetation noise with good agreement.

    Psycho acoustic tests was performed by 36 subjects to determine the signal-to-noise (S/N) ratios when wind turbine noise is inaudible in three different natural ambient noises. The masking threshold varied between -6.5 dBA and -2.7 dBA for coniferous tree noise and sea wave noise respectively. Further tests revealed that at S/N ratios of +3dBA and above the wind turbine noise was considered as the dominant sound source.

  • 348.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Prediction method for vegetation noiseManuskript (Annet vitenskapelig)
  • 349.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Wind Turbine Noise and Natural Sounds: Masking, Propagation and Modeling2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Wind turbines are an environmentally friendly and sustainable power source. Unfortunately, the noise impact can cause deteriorated living conditions for nearby residents. The audibility of wind turbine sound is influenced by ambient sound. This thesis deals with some aspects of noise from wind turbines. Ambient sounds influence the audibility of wind turbine noise. Models for assessing two commonly occurring natural ambient sounds namely vegetation sound and sound from breaking waves are presented in paper A and B. A sound propagation algorithm has been compared to long range measurementsof sound propagation in paper C. Psycho-acoustic tests evaluating the threshold and partial loudness of wind turbine noise when mixed with natural ambient sounds have been performed. These are accounted for in paper D.

    The main scientific contributions are the following.Paper A: A semi-empiric prediction model for vegetation sound is proposed. This model uses up-to-date simulations of wind profiles and turbulent wind fields to estimate sound from vegetation. The fluctuations due to turbulence are satisfactory estimated by the model. Predictions of vegetation sound also show good agreement to measured spectra.

    Paper B: A set of measurements of air-borne sound from breaking waves are reported. From these measurements a prediction method of sound from breaking waves is proposed. Third octave spectra from breaking waves are shown to depend on breaker type. Satisfactory agreement between predictions and measurements has been achieved.

    Paper C: Long range sound propagation over a sea surface was investigated. Measurements of sound transmission were coordinated with local meteorological measurements. A sound propagation algorithm has been compared to the measured sound transmission. Satisfactory agreement between measurements and predictions were achieved when turbulence were taken into consideration in the computations.

    Paper D: The paper investigates the interaction between wind turbine noise and natural ambient noise. Two loudness models overestimate the masking from two psychoacoustic tests. The wind turbine noise is completely concealed when the ambient sound level (A-weighed) is around 10 dB higher than the wind turbine noise level. Wind turbine noise and ambient noise were presented simultaneously at the same A-weighed sound level. The subjects then perceived the loudness of the wind turbine noise as 5 dB lower than if heard alone.

    Keywords: Wind turbine noise, masking, ambient noise, long range sound propagation

  • 350.
    Bolin, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Almgren, Martin
    Ohlsson, Esbjörn
    Karasalo, Ilkka
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Long term estimations of low frequency noise levels over water from an off-shore wind farm2014Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 135, nr 3, s. 1106-1114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article focuses on computations of low frequency sound propagation from an off-shore wind farm. Two different methods for sound propagation calculations are combined with meteorological data for every 3 hours in the year 2010 to examine the varying noise levels at a reception point at 13 km distance. It is shown that sound propagation conditions play a vital role in the noise impact from the off-shore wind farm and ordinary assessment methods can become inaccurate at longer propagation distances over water. Therefore, this paper suggests that methodologies to calculate noise immission with realistic sound speed profiles need to be combined with meteorological data over extended time periods to evaluate the impact of low frequency noise from modern off-shore wind farms.

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