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  • 1.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Aeroacoustics research in Europe: The CEAS-ASC report on 2012 highlights2013In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 332, no 25, p. 6617-6636Article, review/survey (Refereed)
    Abstract [en]

    The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.

  • 2.
    Carbonne, Louis
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Winkler, Niklas
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Use of Full Coupling of Aerodynamics and Vehicle Dynamics for Numerical Simulation of the Crosswind Stability of Ground Vehicles2016In: SAE International Journal of Commercial Vehicles, ISSN 1946-391X, E-ISSN 1946-3928, Vol. 9, no 2, p. 359-370Article in journal (Refereed)
    Abstract [en]

    The prediction in the design phase of the stability of ground vehicles subject to transient crosswinds become of increased concern with drag reduced shapes, lighter vehicles as well as platooning. The objective of this work is to assess the order of model complexity needed in numerical simulations to capture the behavior of a ground vehicle passing through a transient crosswind. The performance of a full-dynamic coupling between aerodynamic and vehicle dynamic simulations, including a driver model, is evaluated. In the simulations a feedback from the vehicle dynamics into the aerodynamic simulation is performed in every time step. In the work, both the vehicle dynamic response and the aerodynamic forces and moments are studied. The results are compared to a static coupling approach on a set of different vehicle geometries. Five car-type geometries and one simplified bus geometry are evaluated. The aerodynamic loads and moments are obtained using Detached Eddy Simulation (DES) where the motion of the vehicle is enabled using an overset mesh technique. This motion is calculated with a single-track model, including a driver model and handling two degrees of freedom, namely lateral translation and yaw motion.

    The results show that for vehicles undertaking large yaw moments and therefore large yaw motions, like the bus-type geometry, the full dynamic coupling is beneficial. In this case, a static coupling overestimates the aerodynamic loads and in turn the vehicle motion. On less crosswind sensitive vehicles, like the car-type geometries, the full-coupling approach does not modify the results in a significant way compared to a static coupling.

  • 3.
    da Rocha-Schmidt, L.
    et al.
    Technische Universität München, Germany.
    Hermanutz, A.
    Technische Universität München, Germany.
    Baier, H.
    Technische Universität München, Germany.
    Seitz, A.
    Bauhaus Luftfahrt e.V., München, Germany.
    Bijewitz, J.
    Bauhaus Luftfahrt e.V., München, Germany.
    Isikveren, A. T.
    Bauhaus Luftfahrt e.V., München, Germany.
    Scarpa, F. L.
    University of Bristol, UK.
    Allegri, G.
    University of Bristol, UK.
    Remillat, C.
    University of Bristol, UK.
    Feuilloley, E.
    University of Bristol, UK.
    Majic, Frane
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Progress Towards Adaptive Aircraft Engine Nacelles2014In: 29th Congress of the International Council of the Aeronautical Sciences, ICAS, International Council of the Aeronautical Sciences , 2014Conference paper (Other academic)
    Abstract [en]

    Emissions and noise of aircraft engineshave to be significantly further reduced andefficiency further increased in the future. Onemeans is the improvement of airflow though theengine and especially so in its inlet region byproper shapes. Due to changes in the flightconditions, the optimal nacelle shape varies. Itwould thus be beneficial to be able to change thenacelle shape. Evaluations on system and enginelevels including related flow simulations supportthe identification of proper shaping parameters.Initial concepts of possible morphingtechnologies are discussed as well.

  • 4.
    Dahan, Jeremy A.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    O'Reilly, Ciarán
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Numerical investigation of a realistic nose landing gear2014In: 20th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2014Conference paper (Other academic)
    Abstract [en]

    A hybrid approach is used to study the noise generated by a realistic full-scale nose land- ing gear configuration. Compressible Detached-Eddy Simulations are performed to com- pute the flow field and the far-field noise is evaluated with the Ffowcs Williams-Hawkings acoustic analogy. Preliminary Reynolds-Averaged Navier-Stokes simulations are performed to evaluate the sensitivity of the steady solution to the computational grid. It is found that mesh independence is not obtained with the grids considered, although the agreement between the medium and fine grids is reasonable. The time-dependent solution obtained via DES is examined and the main noise sources on the gear surfaces are identified. The power spectral density of pressure uctuations on the tyre surface is found to be rather broadband on the noisier sides of the tyre, while distinct humps and a sharp peak near 1kHz are identified in the quieter regions of the tyre. This sharp peak is observed again in the far-field noise. Further work is needed to clarify the cause of this peak. Its frequency is too high to link it with shedding from a gear component, although it could be associated with unsteadiness near the tyre corner.

  • 5.
    Dahan, Jeremy A.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Numerical investigation of the flow around a realistic nose landing gearManuscript (preprint) (Other academic)
    Abstract [en]

    Detached-eddy simulations of the flow around a realistic two- wheeled nose landing gear are conducted, at a Reynolds number corresponding to the final approach phase for a regional aircraft. The main focus is on the flow and associated sound fields in the inter-wheel region and in the wake of the landing gear. Three unstructured grids are designed to evaluate the sensitivity of the solution to grid resolution. The three flow solutions agree well, although the turbulent wake requires a fine mesh. In addition, comparisons with available experimental data on two other nose landing gear models, the PDCC and LAGOON gears, yield a good qualitative agreement. The wake of the landing gear assembly is strongly three-dimensional and exhibits a complex behaviour. The effect of the torque links and wheel axle on the flow dynamics and sound sources were examined via simulations on different configurations. The presence of the torque links and the wheel axle, often simplified or omitted in numerical landing gear studies, were found to strongly modify the flow in the inter-wheel region and in the wheel wakes. The noise was propagated to the far-field using the convective form of the FWH integral. The far- field noise at sideline receivers agrees well with wind-tunnel measurements and the overhead noise sources in the inter-wheel region are identified by considering the integrand of the FWH analogy. 

  • 6.
    Dahan, Jeremy
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Futrzynski, Romain
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    O'Reilly, Ciarán
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Aero-acoustic source analysis of landing gear noise via dynamic mode decomposition2014In: 21st International Congress on Sound and Vibration, ICSV21: / [ed] Malcolm J. Crocker, Marek Pawelczyk, Jing Tian, 2014, Vol. 2, p. 1245-1252Conference paper (Refereed)
    Abstract [en]

    In this paper, we apply dynamic mode decomposition (DMD) on time accurate simulationsof the pressure distribution on a realistic full-scale noselanding gear configuration in order toidentify noise generating structures on landing gear surfaces. The simulated pressure data isobtained from DES simulations using the commercial software STAR-CCM+ by CD-adapco.The dynamics of the surface pressure on a tyre are discussed and the DMD modes are com-puted from instantaneous pressure snapshots. The far-fieldnoise is determined via the FfowcsWilliams-Hawkings analogy, where a given frequency band source term can be reconstructedby choosing an appropriate number of DMD modes.

  • 7.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Biela, Christoph
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Analysis of Aeroacoustic Wave Propagation Simulations Using a Higher-Order Accurate Method2006In: Collection of Technical Papers - 12th AIAA/CEAS Aeroacoustics Conference: Volume 2, 2006, p. 922-931Conference paper (Other academic)
    Abstract [en]

    We present analysis and numerical investigations of the influence of grid stretching together with artificial viscosity on solutions to higher order accurate centered finite difference schemes. Also, we numerically investigate the accuracy of a sixth order accurate scheme for varying Mach number. In the analysis the first-order wave equation together with artificial viscosity terms are considered. In the numerical calculations a simple model problem is solved for which detailed studies of the downstream and upstream acoustic waves is possible.

  • 8.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Forsberg, Nicolas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Nordström, Jan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Simulations of Acoustic Waves in a Turbo-Fan Engine Air Intake2010In: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010Conference paper (Other academic)
    Abstract [en]

    In this work, propagation of acoustic waves in the air intake of an turbo-fan engine are simulated using a commercial Navier-Stokes solver. Three different acoustic modes are studied, the first and second radial mode with no azimuthal variation and the first radial mode with four lobes in the azimuthal direction. From the results it can be concluded that the propagation of sound waves in a curved intake can indeed be simulated using a commercial CFD solver. Also, the acoustic source, when given as a boundary condition, should be set at the fan plane. A strong influence of the flow or the curved geometry is identified, yielding a focusing of sound waves to the middle part of the duct. A transmission loss of the acoustic power from the fan plane to the inlet plane of around 5 dB is identified for the first radial modes for acoustic powers in the interval [128 db, 158 dB]. Non-linear effects are identified for powers of 148 dB and higher, which seems reasonable. Finally, a shielding effect of supersonic regions is identified.

  • 9.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Gong, Jing
    IT-department, Uppsala University.
    Svärd, Magnus
    Stanford University, Standford, USA.
    Nordström, Jan
    IT-department, Uppsala University.
    An Investigation of the Performance of a High-Order Accurate Navier-Stokes Code2006In: ECCOMAS CFD 2006, 2006, p. 11-Conference paper (Refereed)
  • 10.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Kreiss, G.
    Krank, B.
    Analysis of stretched grids as buffer zones in aero-acoustic simulations in two space dimensions2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Conference paper (Refereed)
    Abstract [en]

    A zone of increasingly stretched grid is a robust and easy-to-use way to avoid unwanted reflections at artificial boundaries in aero-acoustic simulations. There are two main damping mechanisms, dissipation and under-resolution of a traveling wave, respectively. In this paper the behavior of acoustic waves in two space dimensions are studied via analysis of solutions to a semi-discrete linear boundary value problem. The solutions of the linear problem is compared to solutions of the linearized Euler equations.

  • 11.
    Efraimsson, Gunilla
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Kreiss, Gunilla
    It Department, Uppsala University, Uppsala.
    Analysis of Stretched Grids as Buffer Zones in Aero-Acoustic Simulations2009In: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009Conference paper (Other academic)
    Abstract [en]

    A zone of increasingly stretched grid is a robust and easy-to-use way to avoid unwanted reections at artificial boundaries in aero-acoustic simulations. There are two main damping mechanisms, dissipation and under-resolution a traveling wave, respectively. In this paper the behavior of acoustic waves and wave packages, respectively, are studied via analysis of solutions to a semi-discrete linear boundary value problem. The solutions of the linear problem is compared to solutions of the full non-linear Euler equations.

  • 12.
    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)
  • 13.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Diedrichs, Ben
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Detached-Eddy Simulations Applied to Unsteady Crosswind Aerodynamics of Ground Vehicles2010In: PROGRESS IN HYBRID RANS-LES MODELLING, Berlin: SPRINGER-VERLAG , 2010, Vol. 111, p. 167-177Conference paper (Refereed)
    Abstract [en]

    Crosswind stability is an important safety issue for manufacturers of cars, buses and rail vehicles. Since side wind conditions are unsteady phenomena they require time-dependent techniques to simulate the flow. In this study, a hybrid RANS-LES methods, Detached-Eddy Simulation, is applied to evaluate headwind and unsteady crosswind situations for a simple model of car. A grid refinement study is carried out to evaluate the accuracy of the calculations. Convergence in the force coefficients while refining the grid suggests that a certain level of grid convergence is reached. A similar conclusion is drawn from the unsteady simulations.

  • 14.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    An Assessment of Detached-Eddy Simulations of Unsteady Crosswind Aerodynamics of Road Vehicle2011In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 87, no 1, p. 133-163Article in journal (Refereed)
    Abstract [en]

    An extensive study of the mesh requirements when simulating unsteady crosswind aerodynamics for industrial applications is conducted and reported in this article. Detached-Eddy Simulations (DES) of a simple car geometry under headwind, steady crosswind and time-dependent wind gust are analysed for different meshes and flow cases using a commercial software, STAR-CD. The typical Reynolds number of the cases studied is 2.0x106 based on the vehicle length. Mesh requirements for capturing the time development of the flow structures during a gust is provided. While respecting these requirements, the aerodynamic coefficients can be reliably calculated. Using turbulence methods like DES in order to resolve the flow scales provides a significant insight for designing a ground vehicle and, due to the reasonable computational times involved, can be incorporated in a design process in a near future.

  • 15.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. 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, VinnExcellence Center for ECO2 Vehicle design.
    Detached-Eddy Simulations of the Effects of Different Wind Gust Models on the Unsteady Aerodynamics of Road Vehicles2010In: ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels (FEDSM2010), 2010, p. 2605-2614Conference paper (Refereed)
    Abstract [en]

    Therelative flexibility of nowadays simulation techniques offers an alternative wayto experiments in order to investigate unsteady crosswind aerodynamics inan industrial framework. In this study, time-accurate simulations, Detached-Eddy Simulations(DES), are used to simulate the flow around a simplevehicle shape, the so-called Windsor model. The ReL of thecorresponding flow case is 2.0 · 106. The influence ofdifferent deterministic models of wind gusts on the aerodynamic loadsand moments are studied. The wind gusts are varied inthe stream-wise and the vertical direction. The magnitude of thegusts models corresponds to a yaw angle of 20°. Theaerodynamic loads calculated show a large excess of drag coupledwith a reduction of the pitch moment. In addition, althoughthe side force has a smooth variation in the gust,overshoots up to 18% higher than the steady value ofyaw moment are also observed.

  • 16.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Effects of Deterministic Wind Gusts on Unsteady Crosswind Aerodynamics of Road Vehicles2009Report (Other academic)
    Abstract [en]

    The relative flexibility of nowadays numerical methods offers an alternative way to experiments in order to investigate unsteady crosswind aerodynamics in an industrial framework. In this study, time accurate methods such as Detached-Eddy Simulations (DES) are used to simulate the flow. A simple vehicle shape, the so-called Windsor model, is chosen for the model. The ReL of the corresponding flow case is 2.0x106. Then, different deterministic models of wind gusts that are varied in the streamwise and the vertical direction are tested. The magnitude of the gusts models corresponds to a yaw angle of 20o. The aerodynamic loads calculated show a large excess of drag coupled with a reduction of the pitch moment. Although the side force has a smooth variation in the gust, overshoots up to 18% higher than the steady value of yaw moment are also observed.

  • 17.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. 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, VinnExcellence Center for ECO2 Vehicle design.
    Numerical study of design alterations affecting the crosswind characteristics of a generic road vehicle model2010In: Eighth World MIRA International Vehicle Aerodynamics Conference, 2010Conference paper (Refereed)
  • 18.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Unsteady mechanisms in crosswind aerodynamics for ground vehicles2011Report (Other academic)
  • 19.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. 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.
    Diedrichs, B.
    Numerical Investigation of Unsteady Crosswind Vehicle Aerodynamics using Time-Dependent Inflow Conditions2008In: Seventh World MIRA International Vehicle Aerodynamics Conference, 2008Conference paper (Refereed)
    Abstract [en]

    Transient disturbances concerning ground vehicles are not only due to rail or road irregularities but are also caused by unsteady ambient wind conditions. This study presents a numerical investigation of unsteady crosswind aerodynamics by using the commercial software STAR-CD from CD-Adapco. The unsteadiness of the aerodynamics is introduced through time-dependent inflow boundary conditions that describe a jet flow according to Schlichting [1]. The purpose of this study is to explore the validity of the commonly used numerical methods (URANS and DES) for the current crosswind application. To this end, simplified vehicle geometries are utilized, for which the experimental results of Chadwick et al. [2] are used as reference data.

  • 20.
    Favre, Tristan
    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.
    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.
    Elofsson, Per
    Scania AB, Truck Chassis Development,Sweden.
    Detached-eddy simulations for steady and unsteady crosswind aerodynamics of ground vehicles2011In: 20th AIAA Computational Fluid Dynamics Conference 2011, 2011Conference paper (Refereed)
    Abstract [en]

    This paper presents Detached-Eddy Simulations (DES) of two generic vehicle models with different design characteristics and different Re numbers under steady and unsteady crosswind conditions. The good agreement with the experimental data available on the first model in gusty conditions demonstrates the capabilities of the combination of transient boundary data together with DES to accurately simulate unsteady crosswind ows for ground vehicles. The second geometry serves to evaluate whether polyhedral meshes with a second order upwind scheme, that is a numerical framework usually employed for RANS in industry, can be used for DES on crosswind ows. The results with the polyhedrals show comparable results with the reference hexahedral mesh and can be effciently used to provide some insights on complex unsteady ows.

  • 21.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Elofsson, Per
    Scania.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Detached-Eddy simulations of simplified vehicles in steady and unsteady crosswindArticle in journal (Other academic)
  • 22.
    Favre, Tristan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Jarlmark Näfver, Jonas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Stensson Trigell, Annika
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Static coupling between detached-eddy simulations and vehicle dynamic simulation of a generic road vehicle model in unsteady crosswind with different rear configurationsArticle in journal (Other academic)
  • 23.
    Favre, Tristan
    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.
    Näfver, Jonas Jarlmark
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Jerrelind, Jenny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stensson Trigell, Annika
    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.
    Static coupling between detached-eddy simulations and vehicle dynamic simulations of a generic road vehicle model with different rear configurations in unsteady crosswind2016In: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 72, no 4, p. 332-353Article in journal (Refereed)
    Abstract [en]

    In this paper, aerodynamic loads of a generic car model obtained from advanced computational fluid dynamics (CFD) simulations are coupled to a vehicle dynamics model to enable the assessment of the on-road response. The influence of four rear configurations is studied. The different configurations yield large differences in yaw moments and side forces, which in turn result in considerable discrepancies in lateral displacements as well as yaw rates. From the simulations, it is seen that through balancing the location of the centre of pressure, the stiffness of the suspension bushings and the cornering stiffness of the tyres, it is possible to obtain stable vehicles in strong crosswind conditions for all four rear designs. The results show that monitoring the location of the aerodynamic centre of pressure with respect to the centre of gravity and the neutral steer point is essential for the possibility of designing stable vehicles in transient crosswind.

  • 24.
    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.

  • 25.
    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.

  • 26.
    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.
    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.
    Analysis of the wake of a half-cylinder by dynamic mode decompositionManuscript (preprint) (Other academic)
    Abstract [en]

    This paper analyzes the dynamic structures in the wake of a half-cylinder protruding from the ground. This relatively simple and smooth geometry allows to create a signicant wake, yet the the location of the detachment point is not predictable from the geometry. The flow over the half-cylinder has a Reynolds number of 32*10^3. It is considered to be incompressible and is simulated by Large Eddy Simulations (LES). The flow field is first described in terms of the time-averages of velocity, pressure, and turbulent kinetic energy. This is the most traditional way to study turbulent flows, and it enables to identify the recirculation regions upstream and downstream of the half-cylinder. The locations of separation and reattachment are also obtained. Then, dynamic structures are extracted by means of dynamic mode decomposition (DMD). The DMD modes have the particularity to oscillate in time at a single given frequency, which renders the dynamics of the flow field more intelligible. It is found that despite a broadband spectrum, all the DMD modes reveal the same type of phenomenon that varies only in scale. By observing the modes at different frequencies, vortices can be followed from their creation in the upstream recirculation region. As they are convected downstream, they merge with bigger and bigger vortices, until they are big enough to influence the whole wake.

  • 27.
    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.
    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.
    Dymode: A parallel dynamic mode decomposition software2015Report (Other academic)
    Abstract [en]

    Dymode is a parallel program that computes dynamic mode decompositions. The code is written in C++ and relies on a number of libraries. Several parameters can be specified in order to control the computational aspects of the program as well as the input and output of the decomposition, particularly how the modes are sorted. Finally, dymode is almost entirely parallel and is therefore particularly suitable for computing the dynamic mode decomposition of large datasets.

    The dymode package also includes dymodem, a Matlab implementation of the code which accepts the same arguments as dymode, when they are relevant, and produces the same output. It can be useful to use dymodem when dealing with smaller datasets, or to validate the output from dymode.

  • 28.
    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.
    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.
    Effect of a SDBD on the drag of a half-submerged cylinder in crossflow2014In: ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels, 3 August 2014 through 7 August 2014, ASME Press, 2014, Vol. 1CConference paper (Refereed)
    Abstract [en]

    In this paper the effect of a SDBD-type plasma actuator on the flow over a half-submerged cylinder is investigated numerically. The actuator is modeled via a body force, which is steady in time and where an exponential decay in space is assumed. First, the parameters in the numerical actuator model are determined for the case of no flow by optimization relative to experimental data. Thereafter, numerical solutions for the case with flow are studied numerically with and without actuation. A grid study is performed to check that the flow structures are resolved in both space and time. The effect of the actuator is examined. Although no significant change is observed when using the optimized parameters, using a stronger body force yields a reduction in drag of the order of 5%.

  • 29.
    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.
    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.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical simulation of a plasma actuator on a half-submerged cylinder2013Conference paper (Other academic)
    Abstract [en]

    In this paper Large Eddy Simulations are used to study the reduction of drag that can be achieved on a half-submerged cylinder by using a type of plasma actuator: the single dielectric barrier discharge. Two body force models, one based on an exponential decrease of the force away from the plasma, the other based on a simplified electric field between the electrodes, are compared to experimental values when the actuator is positioned at the apex of the cylinder in an otherwise quiescent environment. The cylinder is then put in a crossflow, and the exponential-based model, which gives the velocity profiles the closest to the experimental data, is used to simulate the effect of the plasma actuator on such a flow. The reduction in drag is changed as the position of the actuator is varied.

  • 30.
    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.  

  • 31.
    Hammar, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Assembly speed-up for the wave expansion method using a uniform background meshManuscript (preprint) (Other academic)
  • 32.
    Hammar, 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.
    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.
    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.
    Simulation of aerodynamically generated noise propagation using the wave expansion method2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016Conference paper (Other academic)
    Abstract [en]

    A numerical method to simulate aerodynamically generated sound and its propagation is presented in this paper. The flow is solved using both analytical expressions and numer- ical methods. The aeroacoustic source terms are then defined by using the aeroacoustic analogies of Lighthill, Ffowcs-Williams and Hawkings, Powell and Howe, and are evaluated from the flow solutions. The acoustic propagation with these sources is then performed using the wave expansion method. This is a discretization method suitable for solving wave propagation through inhomogeneous potential flows. Two different cases are considered in the study, a co-rotating vortex pair and the flow around a 2D cylinder at Re=150. The fo- cus of the work presented is to show a robust introduction of aeroacoustic sources in a wave expansion acoustic propagation solution procedure. The numerical results are compared to experimental and numerical results from other studies of the same configurations. 

  • 33.
    Hammar, 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.
    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.
    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.
    Simulation of aerodynamically generated sound using hybrid aeroacoustic methods2015In: 10th European Congress and Exposition on Noise Control Engineering, Euronoise, 2015, p. 521-526Conference paper (Other academic)
    Abstract [en]

    A numerical method to simulate aerodynamically generated sound and its propagation is presented in this paper. The transient flow field solution is established using a compressible 2D Navier 6WRNHV VROYHU 7KH VRXUFH WHUPV DUH WKHQ GHILQHG E\ XVLQJ +RZH V vortex sound aeroacoustic analogy and are evaluated from the flow solutions. The propagation of acoustic waves from these sources is then performed using the wave expansion method (WEM). This is a discretization method suitable for solving wave propagation through inhomogeneous potential flows. The method is tested on a flow of a rectangular open cavity. The flow conditions are a free stream Mach number of M=0.5 and Reynolds number of Re=1500.. The numerical results are compared to experimental and numerical results from other studies of the same configuration. 

  • 34.
    Herbst, A H
    et al.
    Bombardier Transportation, Sweden.
    Muld, T W
    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.
    Aerodynamic prediction tools for high-speed trains2014In: International Journal of Rail transportation, ISSN 2324-8378, E-ISSN 2324-8386, Vol. 2, no 1Article in journal (Refereed)
    Abstract [en]

    With high-speed trains, the need for efficient and accurate aerodynamic prediction tools increases, since the influence of the aerodynamics on the overall train performance raises. New requirements on slipstream velocities and head pressure pulse in the revised Technical Specification for Interoperability (TSI) for train speeds higher than 190 km/h are more challenging to fulfil for wide-body trains, like the Green train concept vehicle Regina 250, as well as higher trains, like double-deck trains. In this paper, we give an overview of the results from a project within the Green train programme, where the objective was to increase the knowledge on slipstream air flow of wide body trains at high speeds, to understand the implications of the new requirements on the front shape and to develop a prediction methodology in order to take this into account early in the design cycle. In addition, the front design was in parallel optimized with respect to head pressure pulse and drag.

  • 35.
    Kierkegaard, Axel
    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.
    Allam, Sabry
    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.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Simulations of whistling and the whistling potentiality of an in-duct orifice with linear aeroacoustics2012In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 5, p. 1084-1096Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates a linear aeroacoustic simulation methodology to predict the whistling of an orifice plate in a flow duct. The methodology is based on a linearized Navier-Stokes solver in the frequency domain with the mean flow field taken from a Reynolds-Averaged Navier-Stokes (RANS) solution. The whistling potentiality is investigated via an acoustic energy balance for the in-duct element and good agreement with experimental data is shown. A Nyquist stability criterion based on the simulation data was applied to predict whistling of the orifice when placed in a finite sized duct and experiments were carried out to validate the predictions. The results indicate that although whistling is a non-linear phenomena caused by an acoustic-flow instability feed-back loop, the linearized Navier-Stokes equations can be used to predict both whistling potentiality and a duct system’s ability to whistle or not.

  • 36.
    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.

  • 37.
    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.

  • 38.
    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.

  • 39.
    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.

  • 40.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A Numerical Investigation of Interpolation Methods for Acoustic Analogies2010In: 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010, 2010Conference paper (Other academic)
  • 41.
    Kierkegaard, Axel
    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.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    A numerical investigation of interpolation methods for acoustic analogies2008Report (Other academic)
  • 42.
    Kierkegaard, Axel
    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.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Generation and propagation of sound waves in low mach number flows2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Conference paper (Refereed)
    Abstract [en]

    Aeroacoustic calculations are performed for a two-dimensional configuration of an orifice plate mounted in a straight duct in a low Mach number flow. The flow field is calculated by solving the compressible Navier-Stokes equations by means of a direct numerical simulation, using a high order finite difference scheme. The scheme is based on summation by parts operators and a penalty techniques is used to impose boundary conditions. Methods to decompose an acoustic field into upstream and downstream propagating waves are investigated for use in flows with vorticial structures present. The investigated methods are one formulation of a Two microphone method, and one technique which utilize the relation between acoustic pressure and velocity in an acoustic plane wave.

  • 43.
    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.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Simulations of Duct Whistling with Nyquist Analysis and Linearized Navier-Stokes equations2011In: 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011, 2011Conference paper (Other academic)
  • 44.
    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.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Agarwal, A.
    University of Cambridge, Department of Engineering, United Kingdom.
    Simulations of a liner cell using a frequency-domain linearized Navier-Stokes methodology2013In: 19th AIAA/CEAS Aeroacoustics Conference, 2013Conference paper (Refereed)
    Abstract [en]

    We present numerical simulations of a liner concept, where a thin layer of metallic foam material is located in between the perforated plate and the backing cavity. This liner concept was first presented in Ref 1, where experimental tests showed that the acoustic characteristics of such a liner are nearly independent of both flow and temperature. We use the linearized Navier-Stokes equations in frequency domain to simulate the acoustic waves and the coupling to the hydrodynamic field in the main duct and the liner neck. The effect of the metallic foam is modeled using the Delany-Bazley model. The numerical results are in good agreement with the experimental results presented in Ref 1. In addition, a parameter study on the influence of the flow resistivity of the metallic foam, mean flow speed and mean flow temperature is performed.

  • 45.
    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.

  • 46.
    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.

  • 47.
    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)
  • 48.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. 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.
    Heopffner, Jerome
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Åkervik, Espen
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Henningson, Dan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Identifications of sources of sound in low Mach number flows by the use of flow field eigenmodes2006In: 13th International Congress on Sound and Vibration 2006, 2006, p. 2967-2974Conference paper (Refereed)
    Abstract [en]

    We present a method to study sound generation processes in low Mach Number flows. Instead of the full flow field obtained from e.g a DNS, we consider a base flow together with a time-dependent perturbation ,where the perturbation satisfy the Navier-Stokes equations linearized around the base-flow. In a reduced model the perturbation is approximated by a linear combination of the cigenmodes of a corresponding eigenvalue problem. The behavior in time is determined by the corresponding eigenvalues. Curie's equation is used to calculate the acoustic field. By studying the source terms in Curie's equation, it is possible to identify mechanisms for sources of sound. This makes it possible to study how the different sources of sound depend on different structures of the flow field. We apply the methodology on a two- dimensional flow over a cavity with smoothed corners. Results of acoustic pressure in the far field and source strengths for different superpositions of eigenmodes are presented.

  • 49.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    FREQUENCY-DOMAIN LINEARIZED NAVIER-STOKES EQUATIONS FOR FLOWDUCT COMPUTATIONAL AEROACOUSTICS2012Conference paper (Other academic)
  • 50.
    Kierkegaard, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åkervik, Espen
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Flow field eigenmode decompositions in aeroacoustics2010In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 39, no 2, p. 338-344Article in journal (Refereed)
    Abstract [en]

    In this paper an efficient method to study sound generation processes in low Mach number flows is presented. We apply the methodology on a two-dimensional flow over a cavity with smoothed corners. Instead of the full flow field obtained from, for example a Direct Numerical Simulation (DNS), we use a reduced model based on global modes to obtain the aeroacoustic sources. Global modes are eigenmodes to the Navier-Stokes equations, linearized about a steady base flow. In a reduced model the perturbations from a steady state are approximated by a linear combination of the eigenmodes. The time dependence is determined by the corresponding eigenvalues. Curie's equation is used to calculate the acoustic field, and by studying the source terms in Curie's equation, mechanisms for sources of sound are identified. Results of acoustic pressure in the far-field and source strengths for different superpositions of eigenmodes are presented.

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