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  • 1.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Khodashenas, Niloofar Sayyad
    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 study of nonlinear acoustic properties of perforates using band-limited random excitation information2018In: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, Vol. 3, p. 1818-1825Conference paper (Refereed)
    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.

  • 2.
    Boij, Susann
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Acoustic scattering in ducts and influence of flow coupling2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The subject of this thesis is the acoustic properties offlow duct area expansions and the influence of flow-acousticcoupling at sharp edges. For low Mach number flow, significantinteraction between the sound field and the flow field canoccur at such points of flow separation. A linear analyticalmodel is used to describe the sound field, whereas the meanflow field is modelled as a jet issuing into the larger duct.The scattering coefficients for sound waves incident on thearea expansion are determined by the Wiener-Hopf techniquetogether with a building block method. To achieve a uniquesolution, the unsteady Kutta condition is applied at the sharpedge. The results have been verified through comparison withexperimental data, and the agreement is excellent. Thereflection and transmission coefficients for the plane wave, aswell as the absorption coefficient have been studied, and aquasi-stationary model for the scattering coefficient have beenderived from the analytical model.

    The shear layer emanating from the edge is modelled as avortex sheet, with zero thickness. The vortex sheet is unstablefor all frequencies, and as a real shear layer is unstable onlyup to a critical frequency disturbances, it is a low frequencymodel. In fact, it is the Strouhal number, based on thethickness of the shear layer that determines the stabilityproperties of the shear layer. The dynamics of a finite shearlayer is included in the model by adjusting the edge condition,thus extending the model to higher Strouhal numbers. Inaddition, a method to calculate the absorption of sound due tothe vortex shedding gives a good prediction of experimentaldata. The promising result for the adjusted edge condition andthe possibility to predict the transmitted acoustic far fieldimplies that the jet expansion region, which is neglected inthe model, has indeed a negligible influence on the plane wavesound transmission. Apparently, linear theory is sufficient topredict these phenomena, at least in the low frequencyregion.

    New results, both experimental and theoretical, for the endcorrection of an area expansion are presented. It is shown thatthe end correction varies significantly when the duct widthStrouhal number is around one. For large Strouhal numbers, thenon-flow results are retrieved. An analysis of the duct modesindicates a regime where the flow–acoustic coupling via ahigher order acoustic mode is important. It is shown that thisphenomenon is governed by the Strouhal number and not by theclassical acoustic variables Helmholtz number and Mach number.Finally, the influence of the flow-acoustic coupling on theenergy flow is discussed. It is shown that non-orthogonal ductmodes indicate the Strouhal number region where theflow-acoustic coupling has the strongest influence on the soundfield. Strong coupling to a higher orderacoustic mode isanalysed in some detail. A method to construct a conservativesystem, regarding the vortex sheet as a source/sink term isalso presented.

    Keywords:sound, vortex sheet, flow separation, endcorrection, Strouhal number, non-orthogonal modes, energybalance

  • 3.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    An analysis of the acoustic energy in a flow duct with a vortex sheet2009In: MATHEMATICAL MODELING OF WAVE PHENOMENA / [ed] Nilsson B; Fishman L; Karlsson A; Nordebo S, 2009, Vol. 1106, p. 130-139Conference paper (Refereed)
    Abstract [en]

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

  • 4.
    Boij, Susann
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Energy exchange between sound and flow in a ductManuscript (preprint) (Other academic)
  • 5.
    Boij, Susann
    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.
    Flow effects on the acoustic end correction of a sudden in-duct area expansion2009In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 126, no 3, p. 995-1004Article in journal (Refereed)
    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.

  • 6.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Low frequency sound absorption at sharp edges in flow ducts2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 2390-2397Conference paper (Refereed)
    Abstract [en]

    Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow-acoustic interaction. 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.

  • 7.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Parameter dependence of flow acoustic interaction2006In: Mathematical Modeling of Wave Phenomena / [ed] Nilsson, B; Fishman, L, MELVILLE: AMER INST PHYSICS , 2006, Vol. 834, p. 100-108Conference paper (Refereed)
    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.

  • 8.
    Boij, Susann
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    The acoustic end correction: influence of flow couplingManuscript (preprint) (Other academic)
  • 9.
    Boij, Susann
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    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 duct2013In: Proceedings of Meetings on Acoustics: Volume 19, Issue 1, June 2013, Acoustical Society of America (ASA), 2013, p. 030016-Conference paper (Refereed)
    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.

  • 10.
    Boij, Susann
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Nilsson, B.
    Växjö University, School of Mathematics and Systems Engineering, Sweden.
    Reflection of sound at area expansions in a flow duct2003In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 260, no 3, p. 477-498Article in journal (Refereed)
    Abstract [en]

    An analytical model for scattering at area discontinuities and sharp edges in flow ducts and pipes is presented. The application we have in mind is large industrial duct systems, where sound attenuation by reactive and absorptive baffle silencers is of great importance. Such devices commonly have a rectangular cross-section, so the model is chosen as two-dimensional. Earlier solutions to this problem are reviewed in the paper. The modelling of the flow conditions downstream of the area expansion, with and without extended edges, and its implications for the resulting acoustic modes are discussed. Here, the scattering problem is solved with the Wiener–Hopf technique, and a Kutta condition is applied at the edge. The solution of the wave equation downstream of the expansion includes hydrodynamic waves, of which one is a growing wave. Theoretical results are compared with experimental data for the reflection coefficient for the plane wave, at frequencies below the cut-on for higher order modes. Influence of the interaction between the sound field and the flow field is discussed. A region where the reflection coefficient is strongly Strouhal number dependent is found.

  • 11.
    Boij, Susann
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, B.
    Växjö University, School of Mathematics and Systems Engineering, Sweden.
    Scattering and absorption of sound at flow duct expansions2006In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 289, no 3, p. 577-594Article in journal (Refereed)
    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.

  • 12.
    Boij, Susann
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, B.
    Växjö University, International Centre of Mathematical Modelling School of Mathematics and Systems Engineering, Sweden.
    Sound in flow ducts with sharp edges2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Conference paper (Refereed)
    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.

  • 13.
    Boij, Susann
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Pieters, R.
    Eindhoven University of Technology, Department of Applied Physics, Netherlands.
    Reflection properties of a flow pipe with a small angle diffuser outlet2010In: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 1, 2010, p. 706-712Conference paper (Refereed)
    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.

  • 14.
    Bouchouireb, Hamza
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Pignier, Nicolas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Dahan, Jeremy A.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. Siemens PLM, United Kingdom.
    Identification of noise sources on a realistic landing gear using numerical phased array methods applied to computational data2017In: 23rd AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2017Conference paper (Other academic)
    Abstract [en]

    The aerodynamic sound sources on a realistic landing gear are investigated using numerical phased array methods, based on array data extracted from compressible Detached-Eddy Simulations of the flow. Assuming monopole or monopole in a moving medium propagation, the sound sources are identified in the source region through various beamforming approaches: dual linear programming (dual-LP) deconvolution, orthogonal beamforming and CLEAN-SC. The predicted source locations are in good agreement with previous experimental results performed on the same nose landing gear configuration by industrial and academic partners within the ALLEGRA project. Additionally, the modeled sources are used to generate far-field spectra which are subsequently compared to the ones obtained with the Ffowcs Williams-Hawkings acoustic analogy. The results of the dual-LP approach show a good match between the far-field spectra up to a certain frequency threshold cor- responding to the quality of the mesh used. The results demonstrate the potential of numerical phased array methods as a legitimate modeling tool for aeroacoustic simulations in general and as a tool to gain insight into the noise generation mechanisms of landing gear components in particular. 

  • 15.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Pieper, Timm
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Simulation of Wave Scattering at an Orifice by using a Navier-Stokes Solver2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007, 2007Conference paper (Other academic)
  • 16.
    Elsaadany, Sara
    et al.
    Ain Shams Univeristy, Group for Advanced Resaerch in Dynamic Systems, Faculty of Engineering, Egypt.
    Elnady, Tamer
    Ain Shams Univeristy, Group for Advanced Resaerch in Dynamic Systems, Faculty of Engineering, Egypt.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Optimization of exhaust systems to meet the acoustic regulations and the enginespecifications2011Conference paper (Other academic)
    Abstract [en]

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

  • 17.
    Elsaadany, Sara
    et al.
    Ain Shams Univ, ASU Sound & Vibrat Lab, 1 Elsarayat St, Cairo 11517, Egypt..
    Elnady, Tamer
    Ain Shams Univ, ASU Sound & Vibrat Lab, 1 Elsarayat St, Cairo 11517, Egypt..
    Åbom, Mats
    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.
    ACOUSTIC RESPONSE ANALYSIS OF OIL & GAS PIPELINE NETWORKS TO PREVENT THEIR FATIGUE AND FAILURE2010In: PROCEEDINGS OF THE 17TH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION, INT INST ACOUSTICS & VIBRATION , 2010Conference paper (Refereed)
    Abstract [en]

    In this paper, we present an ongoing project addressing the problem of the adequate design of oil and gas pipeline networks. We are developing an interactive simulation program for dynamic response analysis of fluid flow under steady state pulsating flow conditions in piping networks. It is based on one-dimensional plane wave theory, and employs an efficient transfer matrix approach. This program will build on the existing SIDLAB software. SIDLAB is a combination of software solutions for the analysis of sound propagation inside duct networks. The SIDLAB algorithm is very general and can be used to model one-dimensional sound propagation in any duct network. Nevertheless, the current version of SIDLAB is dedicated to the automotive applications, specifically the design of exhaust systems for internal combustion engine. The main objective of this project is to develop a new SIDLAB module, called SIDLAB Oil&Gas, that can be used to optimally design the pipeline networks in the Oil & Gas Industry. It will be able to predict pressure pulsation levels and acoustic shaking forces, as well as solving performance problems caused by reciprocating equipment or flow generated sources in piping and pipeline systems, and in compressor, pump, control valve, and meter stations.

  • 18.
    Elsaadany, Sara
    et al.
    Ain Shams University, Sound and Vibration Lab., Egypt.
    Elnady, Tamer
    Ain Shams University, Sound and Vibration Lab., Egypt.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Insight into exhaust systems optimization techniques2010Conference paper (Other academic)
    Abstract [en]

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

  • 19.
    Futrzynski, Romain
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Weng, Chenyang
    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.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Numerical study of the Stokes layer in oscillating channel flowManuscript (preprint) (Other academic)
    Abstract [en]

    Oscillating turbulent channel flows present particular physics that proves to be particularly difficult to understand. In this paper, a case where the amplitude of the oscillations at the center of the channel is approximately 15% of the mean velocity and the dimensionless angular forcing frequency is 0.01 was studied using several numerical methods. DNS was performed to serve as reference to which the results from an LES were compared. The LES data was post-processed using both phase averaging and the more recent dynamic mode decomposition (DMD), which extracts coherent structures based on their frequency. It was found that the DMD is not able to extract faint harmonic components of the oscillations, which have been observed with phase averaging and Fourier transforms. It is, however, able to extract accurate profiles of the mean and forcing frequency quantities. Compared to the DNS, the accuracy of the LES results was similar to analytical models, although no single model gives accurate result for every quantity investigated.  

  • 20.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    An Extended Transfer Matrix Approach to Model the Effect of Boundary Layers on Acoustic LiningsManuscript (preprint) (Other academic)
    Abstract [en]

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

  • 21.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows2013Conference paper (Other academic)
    Abstract [en]

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

  • 22.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dazel, Olivier
    University of Maine, Acoustical Labratory, France.
    Prediction of acoustic surface impedance of bulk reacting lining with grazing flow2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, International Institute of Acoustics and Vibrations , 2014, p. 2332-2339Conference paper (Other academic)
    Abstract [en]

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

  • 23.
    Färm, Anna
    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.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    The influence of finite sample size on surface impedance determination of materials with low sound absorpsion at low frequencies2015Conference paper (Refereed)
    Abstract [en]

    The most common noise reducing measure is to add sound absorbing material on the domain boundaries. The boundaries covered by the material may in sumilations be represented by the surface impedance of the material. The impedance can either be modeled or determined experimentally. The experimental determination can be done by the well known standing wave tube method or by a free field method. These free field methods enable impedance determination at any angle of incidence for bulk reacting materials, as opposed to the standing wave tube method that is restricted to normal incidence or locally reacting materials. The method prescribes a point source above the surface and measurements in two points close to the sample surface. From this, the surface impedance can be deduced through the known sound field formulation. Among other things, the impact on the accuracy of the method from the field formulation, signal conditioning and sensor type have been studied in previous work. One major concern is the finite size of the material sample, and its influence on the measurement accuracy. This has previously been investigated for highly absorbing materials and it was shown to be a low frequency problem. Therefore, we focus on the impact of the finite sample in frequencies below 2 kHz. In particular, we relate the magnitude of the impact to the properties of the tested material. Also, the influence of the mounting of the material is analyzed. The study is made through analyzing numerical simulations of the experiment for a variety of setups and materials. Theoretical discussion is provided for deeper understanding of the results. The impact of the finite sample is seen to depend on the material properties, not only the setup as previously shown. Materials with high absorption are shown to be more sensitive to these errors.

  • 24.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB, Sweden.
    Dazel, Olivier
    Absorption of sound at a surface exposed to flow and temperature gradients2016In: Applied Acoustics, ISSN 0003-682x, Vol. 110, p. 33-42Article in journal (Other academic)
    Abstract [en]

    In noise abatement using porous or fibrous materials, accurate determination of the surface impedance representing the absorber is decisive for simulation quality. The presence of grazing flow and non-homogeneous ambient temperature influence the reaction of the absorber and may suitably be included in a modified “effective” surface impedance. In this paper, this approach is applied to a generic case representative for the engine bay of a heavy truck, where porous shields suppress the radiated noise, e.g. during a pass-by noise test. The change in the absorption is determined numerically by solving the wave propagation through a layer of varying temperature and flow adjacent to the impedance surface for different angles of incidence. The study shows significant impact of both flow and temperature, especially for materials with low absorption. The diffuse field absorption coefficient is also derived and although the effect is less pronounced in this case, it is still important in lower frequencies and in the frequency range typical for IC engine noise. The proposed numerical method is shown to be accurate and efficient for determination of the effective impedance and moreover not limited to thin boundary layers.

  • 25.
    Färm, Anna
    et al.
    Scania CV AB, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Glav, Regnar
    Scania CV AB, Sweden.
    On sound absorbing characteristics and suitable measurement methods2012In: SAE Technical Paper 2012-01-1534, 2012, Society of Automotive Engineers, 2012Conference paper (Refereed)
    Abstract [en]

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

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

  • 26.
    Färm, Anna
    et al.
    Centre for ECO Vehicle Design, Scania CV, Södertälje, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    Glav, Ragnar
    Scania CV, Södertälje, Sweden.
    On internal mean flow in porous absorbers and its effect on attenuation properties2013In: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, Vol. 19, p. 1-6Conference paper (Other academic)
    Abstract [en]

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

  • 27.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Edge scattering impact in free field estimation of surface impedanceManuscript (preprint) (Other academic)
    Abstract [en]

    Accurate experimental characterization of sound absorbing materials is important to ensure good quality in simulations of larger systems and to analyze materials with unknown acoustic properties. Free field methods allow characterization of material properties at arbitrary sound incidence, which is advantageous compared to standardized methods. The errors of these methods have been studied, in particular those related to the size of the test samples. These are typically seen as oscillations about the correct value, especially at lower frequencies. The errors have been related to the source position and the sample size, but the impact of the material properties has not been investigated. In this paper, the influence of these properties on the errors are investigated through measurements and numerical simulations. The studies show a dependance on the material properties. The error results both from the pressure scattered at the sample edges and the pressure reflected at the material surface. The scattered field is shown to be stronger for materials with high flow resistivity, although the impact of this field on the result is stronger on materials with low flow resistivity. In addition, a method to reduce these errors based on an analytical formulation of the scattering is proposed. The method is applied to numerical simulations and shown to signicantly reduce the impact of the scattered field on the accuracy of the surface impedance.

  • 28.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. Acoustics department, Scania CV AB, Södertälje, Sweden.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Acoustics department, Scania CV AB, Södertälje, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    On variation of absorption factor due to measurement method and correction factors for conversion between methods2012In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, Volume 11, 2012, Institute of noise control engineering , 2012, p. 9343-9350Conference paper (Other academic)
    Abstract [en]

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

  • 29.
    Färm, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Glav, Ragnar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Pass-by noise simulation: - inuence of trim representationManuscript (preprint) (Other academic)
    Abstract [en]

    The necessity of accurate pass-by noise simulations of vehicles has increased as the requirements on noise levels is becoming stricter. Also, the design of noise reducing measures is needed early in the design process when measurements are not possible to perform. The impact of the sound absorbing materials representation on simulated pass-by noise levels from a truck is analysed in this paper. The material may be fully resolved in FEM, including bulk reaction, or represented by a surface impedance, either at normal or a specic angle of incidence. The first representation requires FEM simulations and more material data. This puts higher demands on input data, and more importantly, prevents the use of BEM simulations which signicantly would improve computational efficiency. The two latter representations may be implemented in BEM. The necessary assumption of local reaction may hold for some materials, but it is not always valid. The simulations presented in this paper show that the local reaction assumption underestimates the effect of sound absorption, giving up to 5 dB higher radiated sound power levels and pass-by noise levels up to 2 dB higher than obtained using the bulk-reacting representation. The difference is shown to depend on the material properties and the position of the source in relation to the noise shields and absorbing parts. The directivity of the radiated noise is not affected, although the regions of largest sound pressure levels are more pronounced. The choice of representation of the material is shown to be important for the simulated pass-by noise levels. To choose the level of complexity in the model, it is important to be aware of the effect this may have on the accuracy of the results in order to draw correct conclusions from the results.

  • 30.
    Holmberg, Andreas
    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.
    Boij, Susann
    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.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    A test rig and experimental procedure to determine the aeroacoustic properties of a splitter plate2009In: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009, p. 2009-3258-Conference paper (Refereed)
    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.

  • 31.
    Kierkegaard, Axel
    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. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A frequency domain linearized Navier-Stokes equations approach to acoustic propagation in flow ducts with sharp edges2010In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 127, no 2, p. 710-719Article in journal (Refereed)
    Abstract [en]

    Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.

  • 32.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Scattering matrix evaluation with CFD in low Mach number flow ducts2009In: Proceedings of the SAE 2009 Noise and Vibration Conference, 2009Conference paper (Other academic)
    Abstract [en]

    We present an efficient methodology to perform calculations of acoustic propagation and scattering by components in ducts with flows. In this paper a methodology with a linearized Navier-Stokes equations solver in frequency domain is evaluated on a two-dimensional geometry of an in-duct area expansion. The Navier-Stokes equations are linearized around a time-independent mean flow that is obtained from an incompressible Reynolds Averaged Navier-Stokes solver which uses a k-ε turbulence model and adaptive mesh refinement. A plane wave decomposition method based on acoustic pressure and velocity is used to extract the up and downstream propagating waves. The reflection of the acoustic waves by the induct area expansion is calculated and compared to both measurements and analytical models. Frequencies in the plane wave range up to the cut-on frequency of the first higher order propagating acoustical mode are considered. The reflection is presented in a scattering matrix form that can be used in acoustical two-port calculations on complex duct systems such as exhaust system mufflers and ventilation systems.

  • 33.
    Kierkegaard, Axel
    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.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Simulations of acoustic scattering in duct systems with flow2010In: 20th International Congress on Acoustics 2010, ICA 2010 - Incorporating Proceedings of the 2010 Annual Conference of the Australian Acoustical Society, 2010, p. 186-191Conference paper (Refereed)
    Abstract [en]

    We present an efficient methodology to perform calculations of acoustic propagation and scattering by geometrical objects in ducts with flows. In this paper a methodology with a linearized Navier-Stokes equations solver in frequency domain is evaluated on a two-dimensional geometry of an in-duct area expansion. The Navier-Stokes equations are linearized around a time- independent mean flow that is obtained from an incompressible Reynolds Averaged Navier-Stokes solver which uses a k-ε turbulence model. A plane wave decomposition method based on acoustic pressure and velocity is used to extract the up- and downstream propagating waves. The scattering of the acoustic waves by the induct area expansion is calculated and compared to experiments. Frequencies in the plane wave range up to the cut-on frequency of the first higher order propagating acoustical mode are considered. The acoustical properties of the area expansion is presented in a scattering matrix form that can be used in acoustical two-port calculations on complex duct systems such as exhaust system mufflers and ventilation systems.

  • 34.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Simulations of the scattering of sound waves at a sudden area expansion2012In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 5, p. 1068-1083Article in journal (Refereed)
    Abstract [en]

    The scattering of acoustic plane waves at a sudden area expansion in a flow duct is simulated using the linearized Navier-Stokes equations. The aim is to validate the numerical methodology for the flow duct area expansion, and to investigate the influence of the downstream mean flow on the acoustic scattering properties. A comparison of results from numerical simulations, analytical theory and experiments is presented. It is shown that the results for the acoustic scattering obtained by the different methods gives excellent agreement. For the end correction, the numerical approach is found superior to the analytical model at frequencies where coupling of acoustic and hydrodynamic waves is significant. A study with two additional flow profiles, representing a non-expanding jet with infinitely thin shear layer, and an immediate expansion, shows that a realistic jet is needed to accurately capture the acoustic-hydrodynamic interaction. A study with several different artificial jet expansions concluded that the acoustic scattering is not significantly dependent on the mean flow profile below the area expansion. The constructed flow profiles give reasonable results although the reflection and transmission coefficients are underestimated, and this deviation seems to be rather independent of frequency for the parameter regime studied. The prediction of the end correction for the constructed mean flow profiles deviates significantly from that for the realistic profile in a Strouhal number regime representing strong coupling between acousticand hydrodynamic waves. It is concluded that the constructed flow profiles lack the ability to predict the loss of energy to hydrodynamic waves, and that this effect increases with increasing Mach number.

  • 35.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    A linearized Navier-Stokes solver for the prediction of sound propagation in duct systems2011In: 40th International Congress and Exposition on Noise Control Engineering 2011 Proceedings: Volume 1, 2011, p. 248-256Conference paper (Other academic)
    Abstract [en]

    This paper is aimed at the development of simulation methodologies suitable both as industrial tools for the prediction of the acoustic performance of flow duct systems, as well as for analyzing the governing mechanisms of duct aeroacoustics.. A frequency-domain linearized Navier-Stokes equations methodology has been developed to simulate sound propagation and acoustic scattering in flow duct systems. The performance of the method has been validated to experimental data and analytical solutions for several cases of in-duct area expansions and orifice plates at different flow speeds. Good agreement has generally been found, suggesting that the proposed methodology is suitable for analyzing internal aeroacoustics.

  • 36.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Acoustic propagation in a flow duct with an orifice plate2008In: PROCEEDINGS OF ISMA 2008: INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING, VOLS. 1-8, 2008, p. 485-495Conference paper (Refereed)
    Abstract [en]

    In this paper we present calculations of sound wave propagation in a straight duct with an orifice plate and a mean flow present. The wave propagation is modelled with a frequency domain linearized Navier-Stokes equations methodology. A two-dimensional approximation is used to an axisymmetric cylindrical geometry, and an appropriate frequency scaling is utilized to account for this. The relation between pressure and density is assumed isentropic and correction for duct damping based on viscous dissipation in the acoustic boundary layers is applied. Calculations are carried out for frequencies in the plane wave range up to the cut-on frequency of the first higher order propagating acoustical mode, and performed with a commercial Finite Element Method code on a quadrilateral mesh with third order shape functions. Results of transmission through, and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement.

  • 37.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Boij, Susann
    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.
    Åbom, Mats
    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.
    Simulations of the Whistling Potentiality of an In-Duct Orifice with Linear Aeroacoustics2010In: 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010, 2010Conference paper (Other academic)
  • 38.
    Na, Wei
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Acoustic characterization of a hybrid liner consisting of porous material by using a unified linearized navier-stokes approach2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics, 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, the acoustic properties of a hybrid liner placed at the end of an impedance tube are investigated using numerical simulations. The hybrid liner constitutes of three components, a perforated plate, a porous layer and a rectangular back cavity. The presence of the porous layer is to enhance the absorptive performance of a liner. The main objective of the paper is to verify the proposed numerical methodology - a unified linearized Navier-Stokes Equations (LNSE) approach. In the unified LNSE approach, the combination of the Helmholtz Equation, LNSE as well as the equivalent fluid model are solved in different regions of the impedance tube. To achieve this, the continuity of the coupling condition between the LNSE and the Helmholtz equation is examined. Another objective is to analyze the effectiveness of the porous material to the acoustic performance of the liner. Acoustic liner simulations with and without porous material, porous material with different flow resistivity are carried out. A good agreement is found between the numerical results and the measurements previously performed at KTH MWL.1 Compared to previous work234, several improvements have been made in the numerical methodology, such as that the energy equation has been added in order to include the damping due to viscous dissipation as well as the thermal dissipation in the vicinity of the perforated plate.

  • 39.
    Na, Wei
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Simulations of acoustic wave propagation in an impedance tube using a frequency-domain linearized navier-stokes methodology2014In: 20th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2014Conference paper (Refereed)
    Abstract [en]

    In this paper, we present analysis of the propagation of acoustic plane waves in an impedance tube, in which a liner is attached at one end of the duct. The purpose is to evaluate a linearized Navier-Stokes solver as a tool to determine the acoustic performance of the liner. The liner considered consists of a perforated plate with several circular holes and a rectangular back cavity. The inuence of parameter variations such as plate thickness, porosity area examined. The prediction of the acoustic characters of the liner is based on the numerical solutions of the linearized Navier-Stokes equations in frequency domain in three space dimensions. The impedance as well as reection coefficients of the liner for frequencies in the plane wave regime are obtained by two-microphone method data, which are compared to experimental data as well as results from a semi-empirical model. The results presented in this paper agree very well with results of the linear semi-empirical model, while there are some discrepancies to the experimental results. The reasons for these discrepancies are not fully understood, but could partly be due to that a linear assumption is not always valid.

  • 40.
    Na, Wei
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical prediction of thermoacoustic instabilities with a V-Flame2016In: 23rd International Congress on Sound and Vibration 2016 (ICSV 23), Athens, Greece 10-14 July 2016, Volume 1 of 6: From Ancient to Modern Acoustics, International Institute of Acoustics and Vibrations , 2016, Vol. 1Conference paper (Refereed)
    Abstract [en]

    In this paper, results from a numerical solver for the Helmholtz equation using the Finite Element Method (FEM) for predicting thermoacoustic instabilities are presented. The one-dimensional n-τ flame model, which is governed by an interaction index n and a time-delay τ as well as a Flame transfer function (FTF) is used for flame source term. We show results for the validation of the numerical solver for the Rijke tube benchmark case with the variation of n and τ in the one-dimensional n-τ model. Thereafter, thermoacoustic instabilities for a V-flame are predicted, for a typical configuration of a dump combustor - a tube with an area expansion. This is a more realistic test case, since a bluff-body flame holder is often used in combustors, where a V-flame will be generated and anchored to the rod. Usually, the V-flame is more susceptible to thermoacoustic instabilities. In the paper, the eigenfrequencies, as well as the acoustic pressure perturbations are presented as numerical results.

  • 41.
    Na, Wei
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Prediction of thermoacoustic instabilities in combustors using linearized Navier-Stokes equations in frequency domain2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, Vol. 2 / [ed] Malcolm J. Crocker ; Francesca Pedrielli ; Sergio Luzzi ; Marek Pawelczyk ; Eleonora Carletti, International Institute of Acoustics and Vibrations , 2015, Vol. 2, p. 2011-2018Conference paper (Refereed)
    Abstract [en]

    The paper presents a numerical methodology for the prediction of the thermoacoustic instabilities with the effects of the mean-flow as well as the viscosity. As an academic standard test case, the configuration within the flame sheet located in the middle of the duct is investigated. First, the ducted flame numerical reference case is solved by the inhomogeneous Helmholtz equations in combination of the n - τ flame model assuming that the flow is at rest. Then, we derive the linearized Navier-Stokes equations (LNSE) in frequency domain in combination of the flame model. The unsteady effect of the flame is modeled by the n - τ flame model in harmonic form, which is essentially a 1D formulation relating the rate of heat release and the acoustic velocity at the reference point.

  • 42.
    Na, Wei
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Simulations of the scattering of sound waves at a sudden area expansion in a 3D duct2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, international Institute of Acoustics and Vibrations , 2014, Vol. 1, p. 1420-1427Conference paper (Refereed)
    Abstract [en]

    The scattering of acoustic plane waves at a sudden area expansion in a duct without flow is simulated using a linearized Navier-Stokes equations solver in frequency domain. The aim is to validate the numerical methodology for three-dimensional simulations, and to investigate the acoustic properties of the area expansion. A comparison of results from numerical simulations, measurements and analytical solutions is presented. It is shown that results for the acoustic scattering obtained by different wave decomposition methods are in excellent agreement.

  • 43.
    Nair, Vineeth
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Inspecting sound sources in an orifice-jet flow using Lagrangian coherent structures2016In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 140, p. 397-405Article in journal (Refereed)
    Abstract [en]

    A novel method is proposed to identify flow structures responsible for sound generation in confined flow past an inhibitor. Velocity fields obtained using Large Eddy Simulations (LES) are post-processed to compute the Finite Time Lyapunov Exponent (FTLE) field, the ridges of which in backward time represent an approximation to Lagrangian Coherent Structures (LCS), the structures that organize transport in the flow field. The flow-field is first decomposed using dynamic mode decomposition (DMD), and the organizing centers or vortices at the significant DMD frequencies are extracted. The results are then compared with the lambda(2) criterion. Features such as shear layer roll-up and development of secondary instabilities are more clearly visible in the FTLE field than with the lambda(2) criterion.

  • 44.
    Nilsson, B.
    et al.
    Växjö University, International Centre of Mathematical Modelling School of Mathematics and Systems Engineering, Sweden.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Acoustic waves in ducts with thin shear layers2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Conference paper (Refereed)
    Abstract [en]

    The acoustic properties of a duct may change radically if a mean flow is introduced. The reflection coefficient may for instance reach a peak greater than one at an abrupt open pipe termination and at sudden area expansions the reflection properties may have a strong Strouhal number dependence. Simulations of these phenomena using a model of an issuing jet with a constant cross-section coupling to the slower or quiescent medium by a vortex layer have compared favourably with experiments. Stability of the flow should have a central role in this flow-acoustic interaction. To investigate the importance of stability for the scattering of sound at edges this paper deals with the study of waves in a duct where the flow is not necessary unstable. An accompanying paper treats the scattering of sound at edges in the duct. The flow-acoustic coupling is modelled with a newly proposed set of coupling conditions relating the fields on both sides of an acoustically thin shear layer. The model is uniform in the Strouhal number s based on the shear layer thickness at the exit. For vanishing s the model agrees with the unstable vortex layer model, the layer is stable for s larger than a transfer Strouhal number and the model reduces to the quiescent case for infinite s. In addition to continuity of sound pressure we use continuity for a quantity, being displacement for vanishing s, velocity for s equals the transfer Strouhal number and pressure gradient for infinite s. The stabilizing mechanism reduces for increasing s the acoustic transverse length scale compared to the corresponding scale for the mean flow. The current paper deals with motivating and using the new coupling conditions to study the waves in a duct. The main purpose is to investigate the properties of the acoustic and hydrodynamic waves as well as their interaction. Of interest is also to verify the required stability properties of the model.

  • 45.
    Nygren, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Rumpler, Romain
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    A study of the interaction between vehicle exterior noise emissions and vehicle energy demands for different drive cycles2019In: 23rd International Congress on Acoustics, ICA, 2019Conference paper (Other academic)
    Abstract [en]

    This initial study investigates the interaction between vehicle noise emissions and the energy required to move the vehicles along different drive cycles. There is a trade-off between reducing noise emissions and at the same time reducing other environmental impacts. A vehicle's energy demand associated with a specific drive cycle may be affected when a different route is chosen between two locations to reduce the noise exposure at certain observer points. The methodology of the study was to use the existing IMAGINE traffic noise model as a source model, and to evaluate the sound exposure level (SEL) at observer points as a function of instantaneous sound pressure level estimates as the source moved from one location to another via two different routes. A noise impact estimate with a linear dependence on the difference between the SEL and a threshold level was proposed. Also, the energy demand for each route was calculated. The results indicated that there is a difference between the two routes if the aim is to reduce the noise exposure or the energy demand. Suggested future research is to further improve the noise impact evaluations in the context of very short durations of exposure.

  • 46.
    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.

  • 47.
    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.

  • 48.
    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.

  • 49.
    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, 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.

  • 50.
    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. 

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