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  • 1.
    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.

  • 2.
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Aeroacoustic Characterization using Multiport Methods2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Noise is a major environmental pollutant, which can inict physical and psychologicalinjury. An important noise contribution stems from aeroacousticsources, which are found in e.g., ventilation ducts, engine exhaust systems andairplane engines.In this thesis, research methods for low Mach number aeroacoustic sourcesin ducts are developed. The basis of the methods is the ability to describe theintrinsic linear properties of the source as an N-port (multiport), where theoutput sound eld is related to the input sound eld and the generated soundeld, all consisting of plane waves. The methods presented are both numericaland experimental. The numerical method treats the passive properties, i.e.,scattering, attenuation and amplication of incident sound, while the experimentalmethod treats the active part (intrinsic sound generation) as well. Themethods are applied in the study of noise generation by a vortex mixer plate,placed in an airow of Mach 0.2, and in the study of acoustic-hydrodynamicinteraction in a T-junction of rectangular ducts.It is found that the accuracy of the experimental methods is signicantly increasedwhen the equations are over-determined, which is achieved by addingadditional microphones to the test rig. In the frequency range studied, themixer plate is found to generate less sound when made exible, without disturbingthe mixing quality.For the numerical method { based on the linearized Navier-Stokes equations,a model of the oscillation of the Reynolds stress (\turbulent damping")due to the acoustic eld is introduced. By comparing with experimental results,it is found that not using this model results in an over-prediction of theamplication at higher frequencies with several factors in magnitude, whileimplementing the model results in a much better agreement.

  • 3.
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Experimental Determination of Aeracoustic Sources in Low Mach Number Internal Flows2010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, the in-duct experimental methods for determining aeroacoustic N-ports of in-duct elements are discussed and improved. The scattering matrix determination methods and the related wave decomposition methods are evaluated from measurements in an empty duct carrying a mean flow. The improvements of a new over-determination method for the source part of the N-port is studied using simulations and measurements; in quiescent air as well as measurements of the flow associated noise of a mixer plate, here a triangular plate inserted at an angle in a duct. The new method is shown to improve suppression of random errors while no improvement is achieved for bias errors.

     

    Further, the methods are applied in the study of two different aeroacoustic phenomena; one is the effect on the flow associated noise of the triangular plate achieved by varying the bending stiffness. For the most resilient plate tested, it is observed that when the Strouhal number of the flow noise coalesce with the Helmholtz number of a specific eigen-mode of the plate, the noise is drastically dampened. There is also a weaker broad band effect.

     

    The other phenomena studied is the amplification and attenuation obtained for sound waves propagating in a T-junction of rectangular ducts. It is found that by adding only 10% of inflow in the side branch relative to that in the main branch, the amplification is heavily increased. By adding another 10% the amplification is again similar to that of no side branch flow. Adding further flow lessens the effects still.

  • 4.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    The Error Suppression of an Experimental Over-Determination of In-Duct Flow Noise Sources2010Inngår i: 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, June 2010, 2010, s. 1-19Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 5.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A test rig and experimental procedure to determine the aeroacoustic properties of a splitter plate2009Inngår i: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009, s. 2009-3258-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A test rig for a study of aero-acoustic phenomena over a sharp edge inside a duct is developed and described. The aero-acoustic losses over the edge are experimentally determined in quiescent air by measurements of a three-port, from which a power balance analysis yields the dissipated acoustic energy. The phenomenon of interest is interaction between the vortices shed by an acoustic wave propagating over a sharp edge and the wave itself. However, this phenomenon require high levels of particle velocity. The levels achieved are low, thus the dominating losses seen in the results are instead due to transfer of acoustic energy from sound waves into vibration energy in the splitter plate. This fact was observed by calculating the two-port scattering matrix over each sidebranch.

  • 6.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    The effect of grazing-bias flow on the self sustained oscillations in a side branch2010Inngår i: 20th International Congress on Acoustics 2010, ICA 2010 - Incorporating Proceedings of the 2010 Annual Conference of the Australian Acoustical Society, 2010, s. 176-181Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The flow-acoustic interaction in a T-junction can result in both amplification and attenuation of incoming waves. The frequency ranges of amplification are mainly governed by the time scales of convection of hydrodynamic instabilities over the side branch opening. With bias flow, i.e. flow through the side branch the amplification can increase or completely vanish. In this paper this effect is studied for a T-junction of rectangular ducts, with a grazing Mach number of 0.1 and a varying bias inflow. When the bias inflow Mach number changes from 0 to 0.01 the amplification is increased severely. Further increasing the bias inflow has the effect of lower the amplification again towards zero at a bias Mach number of 0.05.

  • 7.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2015Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 340, s. 152-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 8.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Kierkegaard, Axel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Weng, Chenyang
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A linearized Navier-Stokes method including turbulence damping2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The result is applied in a study of the linear interaction of the acoustic and the hydrodynamic field in a 2D T-junction, subject to grazing flow at Mach 0.1. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynold's stress, due to the acoustic field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-ε turbulence model. The spatially varying turbulent viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented.

  • 9.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kierkegaard, Axel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Weng, Chenyang
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A Linearized Navier-Stokes Method Including Turbulence DampingArtikkel i tidsskrift (Annet vitenskapelig)
  • 10.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mikael, Karlsson
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows: an experimental investigationInngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet vitenskapelig)
  • 11.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Accurate experimental two-port analysis of flow generated sound2011Inngår i: Sound & vibration, ISSN 1541-0161, Vol. 330, nr 26, s. 6336-6354Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

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

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

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

  • 12.
    Holmberg, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Karlsson, M.
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 13.
    Jansson, Johan
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Vilela De Abreu, Rodrigo
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Degirmenci, Niyazi Cem
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Karlsson, Mikael
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Adaptive stabilized finite element framework for simulation of vocal fold turbulent fluid-structure interaction2013Inngår i: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, s. 1-9Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

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

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

1 - 14 of 14
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