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  • 1.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    CFD of Duct Acoustics for Turbocharger Applications2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. In this work the main focus is the turbocharger compressor and a discussion of turbocharger acoustics and earlier work within the area is presented, giving an insight into its sound generating mechanisms and the damping effect it has on pressure pulses, i.e. incoming waves. However, despite the fact that turbo-charging was developed during the first part of the 20th century, there is not much research results available within the area of centrifugal compressor acoustics.

    To improve the understanding of the acoustics of engine duct components, methods based on compressible Large Eddy Simulation (LES) are explored. With these methods it is possible to capture both the complex flow, with sound generating mechanisms, and acoustic - flow interactions. It is also possible to get a detailed insight into some phenomena by access to variables and/or areas where it is difficult to perform measurements. In order to develop these methods the linear scattering of low frequency waves by an orifice plate have been studied, using an acoustic two-port model. This simple geometry was chosen since the flow has several of the characteristics seen in a compressor, like unsteady separation, vortex generation and shock waves at high Mach numbers. Furthermore the orifice plate is in itself interesting in engine applications, where constrictions are present in the ducts. The results have been compared to measurements with good agreement and the sensitivity to different parameters has been studied, showing an expected dependence on inlet Mach number and difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the short times series available in LES. 

    During the development of new engines the industry uses 1D engine CFD tools. These tools are developed to give performance data, but sometimes also the acoustic pulsations are studied. The duct components are modelled and the turbocharger is often modelled with a map, representing its fluid mechanical properties measured under steady state conditions. An aim in this work has been to study the limitations of the models available in the commercial software GT-Power. The scattering of incoming waves was simulated and the results were compared to measurements, showing a large discrepancy for the compressor and a significant discrepancy for the orifice plate.

  • 2.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Flow Duct Acoustics: An LES Approach2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. Simulations are an important tool for enhanced understanding; they give insight into the flow-acoustic interaction in components where it is difficult to perform measurements. In this work the acoustics is obtained directly from a compressible Large Eddy Simulation (LES). With this method complex flow phenomena can be captured, as well as sound generation and acoustic scattering.

    The aim of the research is enhanced understanding of the acoustics of engine gas exchange components, such as the turbocharger compressor.In order to investigate methods appropriate for such studies, a simple constriction, in the form of an orifice plate, is considered. The flow through this geometry is expected to have several of the important characteristics that generate and scatter sound in more complex components, such as an unsteady shear layer, vortex generation, strong recirculation zones, pressure fluctuations at the plate, and at higher flow speeds shock waves.

    The sensitivity of the scattering to numerical parameters, and flow noise suppression methods, is investigated. The most efficient method for reducing noise in the result is averaging, both in time and space. Additionally, non-linear effects were found to appear when the amplitude of the acoustic velocity fluctuations became larger than around 1~\% of the mean velocity, in the orifice.

    The main goal of the thesis has been to enhance the understanding of the flow and acoustics of a thick orifice plate, with a jet Mach number of 0.4 to 1.2. Additionally, we evaluate different methods for analysis of the data, whereby better insight into the problem is gained. The scattering of incoming waves is compared to measurements with in general good agreement. Dynamic Mode Decomposition (DMD) is used in order to find significant frequencies in the flow and their corresponding flow structures, showing strong axisymmetric flow structures at frequencies where a tonal sound is generated and incoming waves are amplified.The main mechanisms for generating plane wave sound are identified as a fluctuating mass flow at the orifice openings and a fluctuating force at the plate sides, for subsonic jets. This study is to the author's knowledge the first numerical investigation concerning both sound generation and scattering, as well as coupling sound to a detailed study of the flow.With decomposition techniques a deeper insight into the flow is reached. It is shown that a feedback mechanism inside the orifice leads to the generation of strong coherent axisymmetric fluctuations, which in turn generate a tonal sound.

  • 3.
    Alenius, Emma
    Department of Energy Sciences, Lund University, Sweden.
    Mode switching in a thick orifice jet, an LES and dynamic mode decomposition approach2014In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 90, p. 101-112Article in journal (Refereed)
    Abstract [en]

    The dynamics of a confined thick orifice plate jet, at Mach 0.4, are studied with dynamic mode decomposition (DMD), of the velocity from a large eddy simulation (LES). The jet exhibits strong periodic structures, due to an initially laminar shear layer, and a non-deterministic switching is observed between an axisymmetric and an azimuthal jet mode. The DMD captures the shape of these structures as different dynamic modes, but (by definition) not their true time-evolution. In order to study the time-evolution of semi-periodic structures in the flow, such as the jet modes that come and go in time, it is suggested to use DMD for identifying the shape of the structures and then calculate time-coefficients for them, by expressing the velocity field as a linear combination of the most important dynamic modes. These time-coefficients are then shown to capture the physics of the flow; they oscillate at the frequency of the corresponding mode, within an envelope with a non-deterministically varying period, representing the mode switching. Additionally, a time variation of the strength of the jet, represented by mode zero, is found to be related to this switching.

  • 4.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sound Generating Flow Structures in a Thick Orifice Plate Jet2014In: Progress in Turbulence V: Proceedings of the iTi Conference in Turbulence 2012, Cham, Switzerland: Springer, 2014, p. 201-204Conference paper (Refereed)
    Abstract [en]

    The aim of thiswork is to study sound generating flowstructures in a thickcircular orifice plate jet, placed in a circular duct. Large eddy simulations (LES)are performed for two jet Mach numbers, 0.4 and 0.9. Characteristic frequenciesin the flow, and their corresponding flow structures, are identified with dynamicmode decomposition (DMD). The results show that a tonal noise is generated atfrequencies where the jet displays strong ring vortices, in the plane wave range.The main sound generating mechanisms seems to be a fluctuating mass flow at theorifice opening and a fluctuating surface force at the plate sides, caused by the ringvortices. The frequencies are believed to be chosen, and strengthened, by a feedbackmechanism between the orifice in- and outlet.

  • 5.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Large eddy simulations of acoustic-flow interaction at an orifice plate2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 345, p. 162-177Article in journal (Refereed)
    Abstract [en]

    The scattering of plane waves by an orifice plate with a strong bias flow, placed in a circular or square duct, is studied through large eddy simulations and dynamic mode decomposition. The acoustic-flow interaction is illustrated, showing that incoming sound waves at a Strouhal number of 0.43 trigger a strong axisymmetric flow structure in the orifice in the square duct, and interact with a self-sustained axisymmetric oscillation in the circular duct orifice. These structures then generate a strong sound, increasing the acoustic energy at the frequency of the incoming wave. The structure triggered in the square duct is weaker than that present in the circular duct, but stronger than structures triggered by waves at other frequencies. Comparing the scattering matrix with measurements, there is a good agreement. However, the results are found to be sensitive to the inflow, where the self-sustained oscillation in the circular duct simulation is an artefact of an axisymmetric, undisturbed inflow. This illustrates a problem with using an undisturbed inflow for studying vortex-sound effects, and can be of interest when considering musical instruments, where the aim is to get maximum amplification of specific tones. Further, it illustrates that at the frequency where an amplification of acoustic energy is found for the orifice plate, the flow has a natural instability, which is suppressed by non-axisymmetry and incoming disturbances.

  • 6.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    LES of Acoustic-Flow Interaction at an Orifice Plate2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Conference paper (Other academic)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with flow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency ($St \approx 0.4$). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fluctuations.

  • 7.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Scattering of Plane Waves by a Constriction2011In: Proceedings of ASME Turbo Expo 2011, Vol 7, Parts A-C, American Society Of Mechanical Engineers , 2011, p. 1043-1052Conference paper (Refereed)
    Abstract [en]

    Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

  • 8.
    Carlsson, C.
    et al.
    Division of Fluid Mechanics, Department of Energy Sciences, Lund University, Sweden.
    Alenius, Emma
    Division of Fluid Mechanics, Department of Energy Sciences, Lund University, Sweden.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. Lund University, Sweden.
    Swirl switching in turbulent flow through 90 degrees pipe bends2015In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 8, article id 085112Article in journal (Refereed)
    Abstract [en]

    Turbulent flow through 90 degrees pipe bends, for four different curvatures, has been investigated using large eddy simulations. In particular, the origin of the so-called swirl switching phenomenon, which is a large scale oscillation of the flow after the bend, has been studied for different bend curvature ratios. A classification of the phenomenon into a high and a low frequency switching, with two distinct physical origins, is proposed. While the high frequency switching stems from modes formed at the bend, and becomes increasingly important for sharp curvatures, the low frequency switching originates from very-large-scale motions created in the upstream pipe flow.

  • 9.
    Fiorina, B.
    et al.
    CNRS, Laboratoire EM2C, CentraleSupelec, France.
    Mercier, R.
    CNRS, Laboratoire EM2C, CentraleSupelec, France.
    Kuenne, G.
    TU Darmstadt, Institute of Energy and Power Plant Technology, Germany. TU Darmstadt, Darmstadt Graduate School of Energy Science and Engineering, Germany.
    Ketelheun, A.
    TU Darmstadt, Institute of Energy and Power Plant Technology, Germany. TU Darmstadt, Darmstadt Graduate School of Energy Science and Engineering, Germany.
    Avdić, A.
    TU Darmstadt, Institute of Energy and Power Plant Technology, Germany. TU Darmstadt, Graduate School of Computational Engineering, Germany.
    Janicka, J.
    TU Darmstadt, Institute of Energy and Power Plant Technology, Germany. TU Darmstadt, Darmstadt Graduate School of Energy Science and Engineering, Germany.
    Geyer, D.
    Darmstadt University of Applied Sciences, Thermodynamik, Germany.
    Dreizler, A.
    TU Darmstadt, Institute of Energy and Power Plant Technology, Germany. TU Darmstadt, Darmstadt Graduate School of Energy Science and Engineering, Germany.
    Alenius, Emma
    Lund University, Sweden.
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Mechanics. Lund University, Sweden.
    Trisjono, P.
    RWTH Aachen University, Institute for Combustion Technology, Germany.
    Kleinheinz, K.
    RWTH Aachen University, Institute for Combustion Technology, Germany.
    Kang, S.
    Sogang University, Department of Mechanical Engineering, Republic of Korea.
    Pitsch, H.
    RWTH Aachen University, Institute for Combustion Technology, Germany.
    Proch, F.
    University of Duisburg-Essen, Institute for Combustion and Gasdynamics (IVG), Chair for Fluid Dynamics, Germany.
    Cavallo Marincola, F.
    University of Duisburg-Essen, Institute for Combustion and Gasdynamics (IVG), Chair for Fluid Dynamics, Germany.
    Kempf, A.
    University of Duisburg-Essen, Institute for Combustion and Gasdynamics (IVG), Chair for Fluid Dynamics, Germany.
    Challenging modeling strategies for LES of non-adiabatic turbulent stratified combustion2015In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921Article in journal (Refereed)
    Abstract [en]

    Five different low-Mach large eddy simulations are compared to the turbulent stratified flame experiments conducted at the Technical University of Darmstadt (TUD). The simulations were contributed by TUD, the Institute for Combustion Technology (ITV) at Aachen, Lund University (LUND), the EM2C laboratory at Ecole Centrale Paris, and the University of Duisburg-Essen (UDE). Combustion is modeled by a premixed flamelet tabulation with local flame thickening (TUD), a premixed flamelet progress variable approach coupled to a level set method (ITV), a 4-steps mechanism combined with implicit LES (LUND), the F-TACLES model that is based on filtered premixed flamelet tabulation (EM2C), and a flame surface density approach (UDE). An extensive comparison of simulation and experimental data is presented for the first two moments of velocity, temperature, mixture fraction, and major species mass fractions. The importance of heat-losses was assessed by comparing simulations for adiabatic and isothermal boundary conditions at the burner walls. The adiabatic computations predict a flame anchored on the burner lip, while the non-adiabatic simulations show a flame lift-off of one half pilot diameter and a better agreement with experimental evidence for temperature and species concentrations. Most simulations agree on the mean flame brush position, but it is evident that subgrid turbulence must be considered to achieve the correct turbulent flame speed. Qualitative comparisons of instantaneous snapshots of the flame show differences in the size of the resolved flame wrinkling patterns. These differences are (a) caused by the influence of the LES combustion model on the flame dynamics and (b) by the different simulation strategies in terms of grid, inlet condition and numerics. The simulations were conducted with approaches optimized for different objectives, for example low computational cost, or in another case, short turn around.

  • 10.
    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.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. 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, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Reduction of the wake of a half-cylinder using a pair of plasma actuatorsManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, the effect of plasma actuators on separated flows is studied via Large Eddy Simulations (LES) of the incompressible flow over a half-cylinder at a Reynolds number of 32*10^3. One plasma actuator is modeled by a steady body force distribution which is able to replicate the effect of the actuator in a quiescent environment without adding any significant complexity to the numerical simulations. This model is applied at two locations in order to simulate a pair of plasma actuators placed on the surface of the halfcylinder, separated by 20 degrees. Several simulations have been performed with the pair of actuators placed at different angles on the half-cylinder, and the drag reduction is reported for each configuration. It is determined that the actuation is able to achieve up to 10% of drag reduction when one actuator from the pair is placed a few degrees downstream of the separation point of the non-actuated flow. Mean flow quantities obtained in the wake and on the surface of the half-cylinder reveal that the reduction in drag is coupled to a reduction in the size of the recirculating zone as well as a delay of the separation point of up to 10 degrees.

  • 11.
    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.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. 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, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Study of Plasma Actuator Efficiency by Simulation of the Detached Flow Over a Half-Cylinder2016Conference paper (Other academic)
    Abstract [en]

    In this paper, the effect of a numerical model for plasma actuators, in the form of single dielectric barrier discharge, is evaluated. One such plasma actuator is modeled by a steady body force distribution able to replicate the effect of the actuator in a quiescent environment without adding any significant complexity to the numerical simulations. This model is used in Large Eddy Simulations (LES) of the flow over a half-cylinder at a Reynolds number of 32000 , where the actuation is expected to yield a measurable drag reduction. The flow without actuation is first analyzed by mesh refinement and by evaluation of different flow quantities in order the validate the simulation results. Thereafter, the model is used to simulate two actuators placed on the half-cylinder one after another and at four locations chosen so that the mean separation point of the non-actuated flow lies betweenthe two actuators. It is determined that the actuation is able to achieve up to 10% of drag reduction, although this value decreases to 6% when the actuation location is moved.

  • 12. Hodzic, Erdzan
    et al.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Duwig, Christophe
    Szasz, R. S.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    A Large Eddy Simulation Study of Bluff Body Flame Dynamics Approaching Blow-Off2017In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 189, no 7, p. 1107-1137Article in journal (Refereed)
    Abstract [en]

    The mechanisms leading to blowoff were investigated numerically by analyzing bluff body stabilized flame at two conditions: a condition far from blowoff to a condition just prior to blowoff. Large eddy simulations have been used to capture the time dependent, three-dimensional evolution of the field. The results were first validated to available experimental data, showing very good agreement for the flow and overall good agreement for the flame. Changes in the large-scale structures are investigated by means of proper orthogonal decomposition and the wavelet method, elucidating the underlying dynamics of the complex flow-flame interaction of a flame approaching blowoff. Our results reveal that, when the flame approaches blowoff conditions, significant changes are found in the large-scale structures responsible for entrainment of species into the recirculation zone located downstream of the bluff body. Possible causes of this shift in large-scale structures are also discussed, which may be useful for extending the blowoff limits of bluff body stabilized burners.

  • 13.
    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.

  • 14.
    O'Reilly, Ciarán J.
    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, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). 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.
    Bodony, D. J.
    University of Illinois Urbana-Champaign, USA.
    Aero-acoustic simulations of an orifice plate mounted in a low-Mach-number ducted flow2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Conference paper (Other academic)
    Abstract [en]

    Aero-acoustic simulations are performed for an orifice plate mounted in a straight duct in a low-Mach number flow. A two-dimensional flow-field is calculated by solv- ing the Navier-Stokes equations by means of a large-eddy simulation (LES), using a high-order finite difference scheme. The scheme uses summation-by-parts (SBP) finite difference operators with simultaneous approximation terms (SAT) to impose boundary conditions. The flow is decomposed using dynamic mode decomposition (DMD) in order to gain insight into the generation of sound by the flow. The frequency of the higher amplitude modes is shown to agree well the frequencies of the highest amplitude peaks in the power spectral density of the outgoing acoustic waves.

  • 15.
    O'Reilly, Ciarán J.
    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 Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bodony, Daniel J.
    University of Illinois Urbana-Champaign, USA.
    Numerical simulation of flow-induced sound generation from an orifice in a low Mach number ducted flow2011In: 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), 2011Conference paper (Other academic)
    Abstract [en]

    Aero-acoustic simulations are performed for an orifice plate mounted in a straight duct in a low-Mach number flow. The flow field is calculated by solving the filtered Navier-Stokes equations by means of direct numerical simulation (DNS), using a high-order finite difference scheme. The scheme uses summation-by-parts (SBP) finite difference operators with simultaneous approximation terms (SAT) to impose boundary conditions. Both the scattering of the sound (passive part) as well as the sound generation (active part) are studied in the low frequency plane wave range. An acoustic two-port model is applied to describe the sound in the duct. The results are compared with experimental data for the same configuration. The efficiency and robustness of the numerical technique are also examined.

  • 16.
    Winkler, Niklas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Reduced model for the radial turbine based on proper orthogonal decomposition2012In: Institution of Mechanical Engineers - 10th International Conference on Turbochargers and Turbocharging, 2012, p. 419-427Conference paper (Refereed)
    Abstract [en]

    In this work we present a method based on Proper Orthogonal Decomposition (POD) to predict the flow and the losses in a radial turbine. The modelling approach allows continuing the time marching of detailed Large Eddy Simulations (LES) in the parameter space of the problem (i.e. for variations in flow parameters and/or boundary conditions). The purpose is to obtain a reduced model for the turbocharger components and the manifolds of internal combustion engines. The suitability of using POD as a base for the reduced model is demonstrated on a radial turbine of a passenger car engine.

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