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  • 1.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation2012In: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise): FIV2012, Dublin, Ireland, 3-6 July 2012 FLOW-INDUCED VIBRATION, 2012, p. 187-193Conference paper (Refereed)
    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.

  • 2.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, 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 orifices2013In: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, p. 2545-2552Conference paper (Refereed)
    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.

  • 3.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Conference paper (Refereed)
    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.

  • 4.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Acoustic characterization of orifices and perforated liners with flow and high-level acoustic excitation2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow.

    In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results.

    The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies.  

  • 5.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    A systematic uncertainty analysis for liner impedance eduction technology2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 356, p. 86-99, article id 12557Article in journal (Refereed)
    Abstract [en]

    Abstract The so-called impedance eduction technology is widely used for obtaining acoustic properties of liners used in aircraft engines. The measurement uncertainties for this technology are still not well understood though it is essential for data quality assessment and model validation. A systematic framework based on multivariate analysis is presented in this paper to provide 95 percent confidence interval uncertainty estimates in the process of impedance eduction. The analysis is made using a single mode straightforward method based on transmission coefficients involving the classic Ingard-Myers boundary condition. The multivariate technique makes it possible to obtain an uncertainty analysis for the possibly correlated real and imaginary parts of the complex quantities. The results show that the errors in impedance results at low frequency mainly depend on the variability of transmission coefficients, while the mean Mach number accuracy is the most important source of error at high frequencies. The effect of Mach numbers used in the wave dispersion equation and in the Ingard-Myers boundary condition has been separated for comparison of the outcome of impedance eduction. A local Mach number based on friction velocity is suggested as a way to reduce the inconsistencies found when estimating impedance using upstream and downstream acoustic excitation.

  • 6.
    Zhou, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Effect of viscosity on impedance eduction and validation2016In: 21st AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2016Conference paper (Refereed)
    Abstract [en]

    Acoustic liners are a key part for reducing aircraft engine noise. Simulation and optimization of liner properties are critically relying on impedance measurement results, so called impedance eduction technology. Traditionally the effect of viscosity has been assumed to have negligible influence. However this paper shows that viscosity has noticeable influence even at low frequencies. The investigation is based on a comparison study using Linearized Euler equations and Linearized Navier-Stokes equations solved by finite element simulations. In the process of impedance eduction a one-dimensional straightforward method is proposed. Normal velocity and displacement have been obtained and discussed. Impedance results are further implemented into a two-dimensional wave propagation code. Finally simulation results have been compared and validated against experimental data.

  • 7.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Effect of viscosity on impedance eduction and validationManuscript (preprint) (Other academic)
  • 8.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental investigation of an in-duct orifice with bias flow under medium and high level acoustic excitation2014In: International Journal of Spray and Combustion Dynamics, ISSN 1756-8277, Vol. 6, no 3, p. 267-292Article in journal (Refereed)
    Abstract [en]

    This paper experimentally investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested. The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The nonlinear acoustic scattering matrix was identified by a finely controled two-source method. Aeroacoustic modal analysis was introduced based on eigenvalue-decomposition. Acoustic properties, such as impedance, nonlinear scattering matrix and the eigenvalues were compared and discussed. Experimental results also show 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.

  • 9.
    Zhou, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice (AIAA 2013-2128)2013In: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013, p. 1-13Conference paper (Refereed)
    Abstract [en]

    This paper investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested experimentally.The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The so-called Cummings equation was the starting point for the theoretical modelling. It was modified and a novel orifce acoustic discharge coefficient model was developed both for cases with and without bias flow. The model was experimentally validated. With this model the acoustic resistance is obtained by the harmonic balance method, and the results agree fairly well with the experimental results for low frequencies. Experimental results also show that bias flow makes the acoustic properties much 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.  

  • 10.
    Zhou, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lahiri, Claus
    Bake, Fredrich
    Enghardt, Lars
    Comparison of impedance eduction results using different methods and test rigs2014In: 20th AIAA/CEAS Aeroacoustics Conference, 2014Conference paper (Refereed)
    Abstract [en]

    The last twenty years has seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contribute to a continuing effort to gain confidence in results obtained using different test rigs as well as different impedance eduction techniques. The latter includes the use of different equations for solving for the sound field in the lined section. The DLR reference liner sample HR-S2 studied is a locally reacting single degree of freedom Helmholtz resonator liner which has previously been tested at DLR and NASA Langley. In this study it is tested in a smaller scale facility at KTH, but under similar mean flow and sound pressure level conditions as in the previous studies. A good agreement has been obtained for different method under the same plug flow assumption. The same trend but not identical effects of nonlinearity have been obtained with high levels of acoustic excitation. The effect of different flow Mach number assumptions are discussed in connection with the use of the Ingard-Myers boundary condition.

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