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  • 1.
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Assessing precision and accuracy in acoustic scattering matrix measurements2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Acoustic scattering matrices are used to characterize the influence of inline duct elements on the acoustic wave propagation in wave guides.When measuring the properties of these matrices, errors are always present in the results and need to be characterized to make valid statements on the correspondence between model predictions and measurements.In this study the random and systematic errors in acoustic scattering matrix measurements are investigated.Several aspects of the measurement cycle are examined, starting with the determination of the random error on the measured transfer functions between the acoustic source signal and the measured acoustic pressure.The second aspect is the determination of the random error on the scattering matrix coefficients. They are mathematically derived from the measurement data and the error has to be propagated from the data to the coefficients.This is done using uncertainty analyses and the use of linear methods to calculate the uncertainty of the coefficients is investigated.The impedance tube is an essential element of acoustic scattering matrix measurements and the third topic is a description of the systematic errors that can occur in these tubes. The effect of various systematic errors are shown, together with methods to account or reduce them.It is shown that there are still systematic errors remaining, and hypotheses to the source of these errors are discussed.In the last part, the knowledge is put to use to measure the aero-acoustic interaction present at a sudden area expansion.It is shown that the measured acoustic absorption agrees qualitatively with the models, however the deviation between the measurements and predictions are larger than the uncertainty of the measurements.The end correction agrees well with the models at high Strouhal numbers, but the scatter on the measurements at lower Strouhal numbers is too large to identify flow-acoustic interaction effects on the end correction.

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  • 2.
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Measured scattering and absorption coefficients of an area expansion with flow.2018Data set
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    ScatteringCoefficients
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    AbsorptionCoefficients
  • 3.
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Methods and techniques for precise and accurate in-duct aero-acoustic measurements: Application to the area expansion2015Licentiate thesis, monograph (Other academic)
    Abstract [en]

    During the design and commissioning of combustion equipment, combustion associated instabilities are commonly encountered. These thermo-acoustic instabilities can cause undesirable noise, vibrations, local thermal and mechanical stresses in the combustor and are prominent in lean combustion. An often used mathematical tool to predict the instability in combustors is the so called network model where the system under study is subdivided in several subsystems and the acoustic state variables are regarded as the input/output of these subsystems. Solving this system of equations gives rise to the complex Eigen-frequencies of the system which tell if the complete system will have an unstable/stable response for specific operating conditions. In such a model it is critical to know what the influence of each subpart is on the acoustic wave propagation to correctly predict the unstable frequencies of the system. The area expansion is a common element found in combustors and the acoustic properties of the area expansion under quiescent conditions are well known, however in the presence of flow, acoustic flow interactions may occur. These interactions change the acoustic properties and are challenging to model and accurate experimental data is needed to validate the modelling. In this study, measurements of the aero-acoustic properties of an area expansion are presented, however the focus is on the experimental techniques and methods used to obtain accurate and precise measurement data in the plane wave frequency regime. The measurement accuracy of the setup used to determine the passive aero-acoustic properties of the area expansion is assessed by measuring a known impedance. Several sources of errors are identified and methods to account for these error sources are given. It is shown that the microphone impedance affects the measurement results and the upper limit of the measurement accuracy for quiescent measurements is governed by this error. The measurement precision of the setup is assessed using a multi-variate analysis and compared with results obtained from a Monte-Carlo simulation. Also the problem to determine the uncertainty of the measured complex pressures receives attention. Using a framework based on the Hilbert-transform, expressions are derived which estimate the uncertainty on the measured complex value from the background signal spectrum. The obtained knowledge is used to determine the scattering matrix of the area expansion. For the quiescent case, the measured results agree within 1.5% of the absolute values and within 1 degree in comparison with the analytical models. In the case with flow, the errors are slightly larger due to the increased flow-noise but a good correspondence with analytical models is found. Also a sudden sound absorption at high flow speeds and low frequencies is observed.

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    Licentiate Thesis
  • 4.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bake, Friedrich
    German Aerosp Ctr, Inst Prop Technol, Engine Acoust, Berlin, Germany..
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Assessing the stochastic error of acoustic scattering matrices using linear methods2018In: INTERNATIONAL JOURNAL OF SPRAY AND COMBUSTION DYNAMICS, ISSN 1756-8277, Vol. 10, no 4, p. 380-392Article in journal (Refereed)
    Abstract [en]

    To be able to compare the measured scattering matrices with model predictions, the quality of the measurements has to be known. Uncertainty analyses are invaluable to assess and improve the quality of measurement results in terms of accuracy and precision. Linear analyses are widespread, computationally fast and give information of the contribution of each error source to the overall measurement uncertainty; however, they cannot be applied in every situation. The purpose of this study is to determine if linear methods can be used to assess the quality of acoustic scattering matrices. The uncertainty in measured scattering matrices is assessed using a linear uncertainty analysis and the results are compared against Monte-Carlo simulations. It is shown that for plane waves, a linear uncertainty analysis, applied to the wave decomposition method, gives correct results when three conditions are satisfied. For higher order mode measurements, the number of conditions that have to be satisfied increases rapidly and the linear analysis becomes an unsuitable choice to determine the uncertainty on the scattering matrix coefficients. As the linear uncertainty analysis is most suitable for the plane wave range, an alternative linear method to assess the quality of the measurements is investigated. This method, based on matrix perturbation theory, gives qualitative information in the form of partial condition numbers and the implementation is straightforward. Using the alternative method, the measurements of higher order modes are analyzed and the observed difference in the measured reflection coefficients for different excitation conditions is explained by the disparity in modal amplitudes.

  • 5.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Estimating the uncertainty in stepped sine measurements performed under partially stochastic conditions2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Conference paper (Refereed)
    Abstract [en]

    Stepped sine measurements are often performed in environments where there is a large contribution of background noise to increase the signal to noise ratio and obtain more accurate measurements. Due to time constraints or to guarantee the stability of the investigated system a single long measurement is often taken and the statistical properties of the results are based on this single measurement. When the background noise is not completely stochastic in nature, for example there is a tonal component present, the obtained statistics can lead to the wrong results because the underlying assumptions to derive these statistics are violated. In this paper an expression is derived to estimate the uncertainty in a stepped sine measurements based on the background noise spectrum. In this way an accurate estimate of the uncertainty can be obtained even when it is not possible to perform enough statistically independent measurements. The results are based on synchronous demodulation using the Hilbert transform and the expressions are derived both in the continuous and discrete time domain so that they can be easily applied.

  • 6.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental uncertainty analysis of impedance measurements2016In: ICSV 2016 - 23rd International Congress on Sound and Vibration: From Ancient to Modern Acoustics, International Institute of Acoustics and Vibrations , 2016Conference paper (Refereed)
    Abstract [en]

    The study of the interaction between acoustics and flow has a long history, and has attracted many scholars. Consequently the major contributors to acoustic-flow interaction are known and improvements made on models to describe the various interactions, give a relative small impact to the overall effect. To validate these new models, experiments have to be more precise and accurate, otherwise no valid statement can be made if the measurements are agreeing with the improved models. The flow-acoustic interaction is commonly measured using impedance tubes through which a flow flows. In this paper, a linear uncertainty analysis is presented to determine the precision of the obtained impedance results. Such kind of analysis has been already reported in literature, but in this paper, the analysis has been expanded to include more uncertain variables and the method is investigated to show the limitations of such an analysis. As an application of the analysis, the measurement of a known impedance without flow has been analyzed, revealing the presence of bias errors in the measurement setup.

  • 7.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    The acoustic equivalence of a mass and heat source2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Conference paper (Refereed)
    Abstract [en]

    In combustion systems, unsteady heat release acts as a source term to the acoustic field within the combustor and under the right conditions the energy of the acoustic field can exponentially grow, leading to a combustion instability. An acoustic driver such as a loudspeaker or horn also acts as a source term to the acoustic field and is often modelled as a fluctuating mass source. Considering the similarity of the flame and the acoustic driver to acts as a source to the acoustic field, the question arises if these two types of sources can be interchanged. This contribution investigates that question by considering a 1-D system with mean flow. In the governing equations a mass source term is included which is linearly related to velocity fluctuations. The results are compared with that of a system with a compact heat source. It is found that the two systems are equivalent when there is no mean flow. In the presence of flow, the response of both systems can approximately be the same when special conditions are met. 

  • 8.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental investigation of the aero-acoustic interaction at an area-expansion2019In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 457, p. 197-211Article in journal (Refereed)
    Abstract [en]

    Experimental results on the aero-acoustic interaction at an area expansion are scarce. In this study, new experimental data is acquired of the aero-acoustic interaction at an area expansion and compared with recent modeling efforts. The aero-acoustic interaction at an area expansion with expansion ratio eta = 0.309 is investigated by measuring the scattering matrix for plane waves at 5 different flow speeds in the incompressible regime. The experimental results are complimented with a comprehensive uncertainty analysis to determine the precision of the data. The scattering coefficients together with derived quantities such as absorption coefficients and dimensionless end corrections are compared against recent analytical results. It is shown that there is consistent deviation between the models and measurement results for certain scattering coefficients. The measured end correction on Strouhal number close to the critical Strouhal number shows a relatively abrupt change. This in comparison with the models, where the change is predicted to be more gradual. Similar observations are made for the absorption coefficient for waves incident upstream of the area expansion, although a qualitative comparison is difficult to make in this case because of the strong influence of the flow downstream of the area-expansion on the results.

  • 9.
    Peerlings, Luck
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Arteaga, Ines Lopez
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Aero-acoustic characterization of the sudden area expansion2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, p. 2174-2181Conference paper (Refereed)
    Abstract [en]

    In combustion devices, thermo-acoustic instabilities are often encountered and are formed by the complex interaction between acoustics, hydrodynamics and combustion. A common geometrical feature found in these devices is the sudden area expansion. Downstream of the area expansion a recirculation zone is formed together with an unstable shear layer when flow is present. This shear layer creates a pathway for interactions between the acoustic and the hydrodynamic field and this interaction could be a precursor for thermo-acoustic instabilities. The work presented here takes a step to gain more insight into these interactions by experimentally investigating the aero-acoustic properties of a sudden area expansion with mean flow. The aero-acoustic properties are characterized by a linear two port model and the scattering matrix representation is used to relate the state variables up-and downstream of the area expansion. The scattering coefficients of the area expansion have been determined for frequencies up to the first cut on frequency of the duct system and for a range of subsonic flow speeds. The measurements have been performed by applying a stepped sine excitation as sound excitation and by using the multi-microphone method.

  • 10.
    Surendran, Aswathy
    et al.
    Keele Univ, Sch Chem & Phys Sci, Keele ST5 5BG, Staffs, England..
    Heckl, Maria A.
    Keele Univ, Sch Chem & Phys Sci, Keele ST5 5BG, Staffs, England..
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Hirschberg, Avraham
    Eindhoven Univ Technol, Dept Appl Phys, NL-5600 MB Eindhoven, Netherlands..
    Aeroacoustic response of an array of tubes with and without bias-flow2018In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 434, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Heat exchangers, consisting of tube arrays in a cross-flow are a vital component of power generation systems. They are of interest from an acoustic point of view, because they can reflect, transmit and absorb an incident sound wave; in other words, they have the potential to act as a sound absorber and even as a passive control device to prevent a thermoacoustic instability in the power generation system. This paper presents a fundamental study of the aeroacoustic response of a tube array with and without bias-flow (also called cross-flow). The study has a theoretical and experimental side. On the theoretical side, a new model, based on the assumption of quasi-steady flow, was developed to predict the acoustic reflection and transmission coefficient of a tube array with bias-flow. Also, the model by Huang and Heckl (Huang and Heckl, 1993, Acustica 78, 191-200) for the case without bias-flow was evaluated. On the experimental side, flow-duct experiments using a multi-microphone technique were performed to validate the predictions from both models. The agreement was found to be very good for low frequencies. The measurements revealed the limit of validity of the quasi-steady model in terms of the Strouhal number. Although this limit is quite low, our quasi-steady model can serve as a valuable tool for designers of heat exchangers.

  • 11. Weng, C.
    et al.
    Otto, C.
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Enghardt, L.
    Bake, F.
    Experimental investigation of sound field decomposition with2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics, 2016Conference paper (Refereed)
    Abstract [en]

    The DUct aCoustic Test rig with Rectangular cross section (DUCT-R) is designed at the German Aerospace Center (DLR), Engine Acoustics Department, to test commercial aircraft engine nacelle liner samples. An air flow with speed up to Mach 0.3 can be achieved in the liner section. An overall number of 106 microphone positions are spread over the rig, making it capable of investigating the scattering of the fundamental and higher order acoustic modes above the liner samples. In this paper, the DUCT-R facility is described. The measurement setups currently being used at DLR are introduced. In addition, a methodology for decomposing measured sound-field data with fundamental and higher order modes is described. The methodology is applied to data sets obtained from a “zero measurement” (a measurement without liner samples) with and without mean flows for validation purposes. The validation results are reported and discussed. 

  • 12.
    Zhang, Zhe
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Tiikoja, Heiki
    KTH.
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Experimental Analysis on the 'Exact' Cremer Impedance in Rectangular Ducts2018In: SAE technical paper series, ISSN 0148-7191, Vol. 2018-June, no JuneArticle in journal (Refereed)
    Abstract [en]

    Cremer impedance, first proposed by Cremer (Acustica 3, 1953) and then improved by Tester (JSV 28, 1973), refers to the locally reacting boundary condition that can maximize the attenuation of a certain acoustic mode in a uniform waveguide. One limitation in Tester's work is that it simplified the analysis on the effect of flow by only considering high frequencies or the 'well cut-on' modes. This approximation is reasonable for large duct applications, e.g., aero-engines, but not for many other cases of interest, with the vehicle intake and exhaust system included. A recent modification done by Kabral et al. (Acta Acustica united with Acustica 102, 2016) has removed this limitation and investigated the 'exact' solution of Cremer impedance for circular waveguides, which reveals an appreciable difference between the exact and classic solution in the low frequency range. Consequently, the exact solution can lead to a much higher low-frequency attenuation level. In addition, the exact solution is found to exhibit some special properties at very low frequencies, e.g., a negative resistance. In this paper, liners designed on the basis of the exact solution are tested and the difference between the exact and classic solution in the low frequency range (not low enough to go into the negative resistance region) is experimentally investigated.

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