Ändra sökning
Avgränsa sökresultatet
12 51 - 97 av 97
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51.
    King, Ulrich
    et al.
    Bauhaus Luftfahrt e.V., Germany.
    Seitz, Arne
    Bauhaus Luftfahrt e.V., Germany.
    Bijewitz, Julian
    Bauhaus Luftfahrt e.V., Germany.
    Hermanutz, Andreas
    Technical University of Munich, Germany.
    da Rocha-Schmidt, Luiz
    Technical University of Munich, Germany.
    Scarpa, Fabrizio
    University of Bristol, United Kingdom.
    Majić, Frane
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Shape adaptive technology for aircraft engine nacelle inlets2016Ingår i: The Royal Aeronautical Society's 5th Aircraft Structural Design Conference, 2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The ambitious emission reduction goals defined by the Advisory Council for Aviation and Innovation in Europe (ACARE), demand new technologies enabling ways to significantly improve aircraft performance. In the European Commission funded low Technology Readiness Level (TRL) project “Morphing Enabling Technologies for Propulsion System Nacelles” (MorphElle) conducted between October 2013 and November 2015, an initial investigation took place to modify the inlet of an Ultra-High Bypass Ratio turbofan nacelle with adaptive structure technology to enhance its aerodynamic performance. The goal was to be able to adopt the inlet lip to different flight conditions and therefore, increase engine performance while at the same time reducing the aerodynamic nacelle drag. A pool of concepts for an adaptive nacelle inlet was established and a down selection was performed and the most promising identified. The selected concept was further elaborated and the impact at aircraft level was examined. Designing an adaptive structure mechanism for the circular shape of a nacelle inlet has different requirements compared to an adaptive structure mechanism, for example, a flap or a slat. For a circular shape, the deformation of the adaptive mechanism in circumferential direction has to be considered as well. A structural concept was established, which consists of flexible outer skin with pneumatic tubes as actuators, which is able to handle the deformation in circumferential direction. With this mechanism it is possible to change the inlet of the used reference nacelle geometry. Numerical tools were used to perform structural and aerodynamic simulations. The results of these simulations served as input for an aircraft assessment. The inputs were nacelle weight, nacelle aerodynamic drag and thrust specific fuel consumption of the engine. With this data an aircraft model was set up and compared to two reference aircraft. The first reference aircraft is a year 2000 reference (comparable to Airbus A330-300). The second reference aircraft is similar to an Airbus A330-300 with projected Entry-Into-Service (EIS) 2025+. For the aircraft equipped with the adaptive nacelle an EIS of 2025+ was assumed as well. The results were that the adaptive nacelle showed improved values for SFC and nacelle aerodynamic drag compared to the reference nacelle geometry. Furthermore, a first prototype of the shape adaptive mechanism as proof of concept was developed. 

  • 52.
    Krank, Benjamin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Evaluating stretched grids and introducing black hole layers as alternative non-reflecting buffer zone2013Ingår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Grid-stretching is often used close to non-reflecting boundaries in order to under-resolve and dissipate outgoing acoustic waves. The resulting buffer zones may be large and computationally expensive, however, since the stretching factor is strongly limited. Two approaches of implementing grid-stretching are considered: Taylor expansion and transformation in curvilinear coordinates. Besides grid-stretching, a new buffer zone technique is introduced, which allows for larger stretching factors and computationally more efficient buffer zones. The speed of sound is varied locally in the buffer zone resulting in spatial under-resolution of outgoing waves similarly to stretched grids. The approach is derived from the concept of acoustic black holes, a method of reducing reflection of bending waves from edges of physical plates, giving the name black hole layer to the new concept. The approach is verified and the performance of stretched grids and black hole layers is evaluated using a linearized Euler equations solver in two space dimensions for several benchmark flows. The most efficient buffer zone is found to be a combination of grid-stretching using Taylor expansion and black hole layer.

  • 53.
    Kreiss, G.
    et al.
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Efraimsson, Gunilla
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Nordstrom, J.
    FFA, Sweden; Uppsala University, Department of Scientific Computing, Sweden.
    Elimination of first order errors in shock calculations2001Ingår i: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 38, nr 6, s. 1986-1998Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First order errors downstream of shocks have been detected in computations with higher order shock capturing schemes in one and two dimensions. Based on a matched asymptotic expansion analysis we show how to modify the artificial viscosity and raise the order of accuracy.

  • 54.
    Kreiss, G.
    et al.
    Uppsala University, Department of Information Technology, Sweden.
    Krank, B.
    Technical University of Munich, Institute for Computational Mechanics, Germany.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Analysis of stretched grids as buffer zones in simulations of wave propagation2016Ingår i: Applied Numerical Mathematics, ISSN 0168-9274, E-ISSN 1873-5460, Vol. 107, s. 1-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A zone of increasingly stretched grid is a robust and easy-to-use way to avoid unwanted reflections at artificial boundaries in wave propagating simulations. In such a buffer zone there are two main damping mechanisms, dissipation and under-resolution that turns a traveling wave into an evanescent wave. We present analysis in one and two space dimensions showing that evanescent decay through under-resolution is a very efficient way to damp waves. The analysis is supported by numerical computations.

  • 55.
    Kreiss, Gunilla
    et al.
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Efraimsson, Gunilla
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Approximate solutions to slightly viscous conservation laws2004Ingår i: Quarterly of Applied Mathematics, ISSN 0033-569X, E-ISSN 1552-4485, Vol. 62, nr 1, s. 117-133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study an approximate solution of a slightly viscous conservation law in one dimension, constructed by two asymptotic expansions that are cut off after the third order terms. In the shock layer, an inner solution is valid and an outer solution is valid elsewhere. Based on the stability results in [10], we show that for a given time interval the difference between the approximate solution and the true solution is not larger than o(epsilon), where epsilon is the viscosity coefficient. The result holds for shocks of any strength.

  • 56.
    Kårekull, Oscar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Fläkt Woods, Jönköping, Sweden .
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik.
    Comparison of RANS parameters for flow noise prediction2013Ingår i: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life, OAL-Osterreichischer Arbeitsring fur Larmbekampfung , 2013, s. 5916-5925Konferensbidrag (Refereegranskat)
    Abstract [en]

    TThe use of Computational Fluid Dynamics (CFD) and especially Reynolds Averaged Navier Stokes Equations (RANS) simulations is a well-established tool in industry for performance evaluation of constrictions in low speed flow ducts. However, the use of CFD simulations for noise predictions is not as common. In this paper, two different models to predict the sound spectra through the use of RANS simulations and a noise reference spectrum are compared and evaluated. One method predicts the sound based on the pressure drop whereas the other method is based on the turbulent kinetic energy. The influence of both turbulence models as well as mesh properties have been investigated. Noise predictions from simulation results are compared to noise measurement results of an orifice in a duct. The comparison between the simulated results and measured data are in excellent agreement. The benefit of using the pressure drop, as input data, is a lower sensitivity to both the structure and the resolution of the mesh. Also, this model has a more general definition allowing a consistent method for different constriction geometries. Still, predictions using the turbulent kinetic energy result in equivalent accuracy and even if the choice of input data is more complex it can be preferred in special cases.

  • 57.
    Kårekull, Oscar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    CHALLENGES AND OPPORTUNITIES FOR FLOW NOISE PREDICTION IN HVAC SYSTEMS2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the possibilities of noise prediction in Heating Ventilation and Air Conditioning (HVAC) systems using semi empirical scaling laws. An approach is presented where the general noise reference spectra are combined with Reynolds Average Navier Stokes (RANS) simulations. Focus is at applying the suggested noise prediction approach to common HVAC components but also to discuss the properties of the prediction model, e.g. radiation characteristics and chosen reference spectra. A model is presented, using a momentum flux assumption of the noise sources, which is validated by a range of HVAC components of both high and low pressure loss.

  • 58.
    Kårekull, Oscar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Prediction model of flow duct constriction noise2014Ingår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 82, s. 45-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The scaling law for aerodynamic dipole type of sound from constrictions in low speed flow ducts by Nelson and Morfey is revisited. A summary of earlier published results using this scaling law is presented together with some new data. Based on this, an effort to find a general scaling law for the sound power for components with both distinct and non-distinct flow separation points are made. Special care is taken to apply the same scaling to all data based on the pressure drop. Results from both rectangular and circular ducts, duct flow velocities from 2 to 120 m/s and sound power measurements made both in ducts and in reverberation chambers are presented. The computed sound power represents the downstream source output in a reflection free duct. In particular for the low frequency plane wave range strong reflections from e.g. openings can affect the sound power output. This is handled by reformulating the Nelson and Morfey model in the form of an active acoustic 2-port. The pressure loss information needed for the semi-empirical scaling law can be gained from CFD simulations. A method using Reynold Average Navier Stokes (RANS) simulations is presented, where the required mesh quality is evaluated and estimation of the dipole source strength via the use of the pressure drop is compared to using the turbulent kinetic energy.

  • 59.
    Kårekull, Oscar
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Fläkt Woods, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Revisiting the Nelson-Morfey scaling law for flow noise from duct constrictions2015Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 357, s. 233-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The semi empirical scaling law by Nelson and Morfey [1] predicts the noise generation from constrictions in ducts with low Mach number flows. The results presented here demonstrate that the original model loose accuracy for constrictions of high pressure loss. An extension based on a momentum flux assumption of the dipole forces is suggested and is evaluated against measurement results for orifice geometries of higher pressure loss than earlier evaluated. A prediction model including constrictions at flow duct terminations is also suggested. Improved accuracy for the predictions of the new model are found for orifice geometries of both high and low pressure loss inside and at end of ducts. The extended model is finally evaluated by measurementson a regular ventilation air terminal device.

  • 60.
    Majić, Frane
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Aero-acoustic performance of adaptive nacelle inlet2015Ingår i: 21st AIAA/CEAS Aeroacoustics Conference, 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The aero-acoustic investigation of the fan noise propagation is conducted. The fan noise is propagated through the series of adaptive inlet shapes of turbofan engine toward the far field. The inlet shape adaptation is made by changing position of one points on the front part of the inlet contour. The investigation is performed without the influence of the mean flow. The propagation of two acoustic modes was investigated, the combination of first radial mode with first and the second circumferential mode. The intensity and directivity of the fan noise in the far field is observed. A finite element solver for convected Helmholtz equation is used in the inner part of the inlet, with perfectly matched layer boundary condition close to the inlet entrance. The outer part of domain is coupled and solved by Kirchoff integral method. The results showed the influence of the inlet shape adaptation on the noise intensity level as well as the directivity of propagation.

  • 61.
    Majić, Frane
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Aerodynamic performance of the adaptive nacelle inlet2015Ingår i: 33rd AIAA Applied Aerodynamics Conference, 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The numerical aerodynamic investigations of an adaptive turbofan-engine inlet is per-formed. The adaptation is made on the front inner part of the inlet by changing positionsof two contour knots, which mimic the possible inlet structure morphing. The numericalcalculations are performed using Reynolds Averaged Navier-Stokes (RANS) simulations forthe climb condition. The evaluation of the aerodynamic performance is based on the inlettotal pressure recovery, DC60 parameter and standard deviation of the normal velocity atthe fan plane. The results exhibit common trend which is a shift of the evaluated parame-ters towards benecial level by increasing the radial position of the rst knot at the inletshape region which is close to the leading edge. Alteration of second knot, which is moredistant from leading edge, results in benecial performance for several inlet shapes. For allparameters, the same group of inlet shapes was isolated as a group of best performance.

  • 62.
    Majić, Frane
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Potential improvement of aerodynamic performance by morphing the nacelle inlet2016Ingår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 54, s. 122-131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work numerical investigations of the aerodynamic performance of an adaptive turbofan-engine inlet is performed. The adaptation is made on the inner front part of the symmetric inlet by changing the positions of two contour knots, which acts as a possible inlet struc- ture morphing. The contour knots are moved in the axisymmetric and radial directions of the inlet, respectively. The numerical calcula- tions are performed using Reynolds Averaged Navier-Stokes (RANS) simulations and are made for climb and cruise flight conditions. The evaluation of the aerodynamic performance is based on the absolute total pressure recovery at the fan plane. The results show that the adaptation of only a small part of the inlet contour gives benefits in the performance at different flight conditions. The radial position in- crease of the knot closer to the leading edge gives overall increase of the pressure recovery level for both flight conditions. The radial posi- tion change of the knot close to the throat diameter leads to the global maximum of absolute total pressure recovery almost independent of the axial position change of the same knot, for both flight conditions. These maximums are attained at different radial positions of the knot close to the throat diameter, for the two flight conditions.

  • 63.
    Majić, Frane
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    The influence of an adaptive nacelle inlet lip on fan noise propagation2016Ingår i: Proceedings of Meetings on Acoustics, ISSN 1939-800X, Vol. 28, nr 1, s. 1-10, artikel-id 030004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aeroacoustic performance of an adaptive inlet of a turbo-fan engine is numerically investigated. The sound intensity and directivity of fan noise propagation to the far-field, and the sound level at lateral reference points are investigated. The investigation is performed for three Helmholtz numbers, with the influence of the mean flow, for a single duct mode. A finite element solver for Helmholtz equation is used in the inner part of the inlet, with a perfectly matched layer boundary condition close to the inlet entrance. The propagation through the outer part of domain is solved by Kirchhoff integral method. The results show the influence of the inlet shape adaptation on the noise intensity level as well as the directivity of propagation. The maximum peak intensity level of all inlet shapes is increased by increasing the Helmholtz number. This causes the width of intensity distribution to become narrower and shifted towards the symmetry axis of the nacelle. The inlet shape with the most opened nacelle throat has the lowest peak and an intensity distribution shifted towards the symmetry axis, which indicates the influence of the mean flow. Also, the more closed nacelle throat causes a decrease of the effective perceived noise level. 

  • 64.
    Majić, Frane
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    The influence of an adaptive nacelle inlet lip on fan noise propagation2016Ingår i: 22nd International Congress on Acoustics, 2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The aeroacoustic performance of an adaptive inlet of a turbo-fan engine is numerically investi- gated in this paper. The sound intensity and directivity of the fan noise propagation to the far-field, and the sound level at lateral reference points are investigated. The investigation is performed for three Helmholtz numbers, with the influence of the mean flow included, for a single duct mode (- 8,1). The contour was defined by five movable knots at the leading edge of the inlet. The contour had to fulfil two constraints, namely it had to have a constant length and a convex curvature. The process of contour adaptation was performed in two steps. In the first step, two knots on the inner inlet side were moved in order to attain a certain shape, while other knots were kept fixed. In the second step, the rest of the knots were moved in order to fulfill the constraints. A finite element solver for the Helmholtz equation is used in the inner part of the inlet, with a perfectly matched layer boundary condition close to the inlet entrance. The propagation through the outer part of domain is solved by Kirchhoff integral method. The results show the influence of the inlet shape adaptation on the noise intensity level as well as the directivity of propagation. The maximum peak intensity level of all inlet shapes is increased by increasing the Helmholtz number. This causes the width of intensity distribution to become narrower and shifted towards the symmetry axis of the nacelle. The inlet shape with the most opened nacelle throat has the lowest peak and an intensity distribution shifted towards the symmetry axis, which indicates the influence of the mean flow. Also, the more closed nacelle throat causes a decrease of the effective perceived noise level. 

  • 65.
    Muld, Toma. W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Henningson, D. S.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mode decomposition of flow structures in the wake of two high-speed trains2012Ingår i: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 98Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two different train geometries, the Aerodynamic Train Model (ATM) and the CRH1, are studied in order to compare the flow structures in the wake. The flow is simulated with Detached Eddy-Simulation and then decomposed into modes with Proper Orthogonal Decomposition. This study has found that the flow structures are indeed different for the two train models although the tails are rather similar. For the CRH1 the dominant flow structures twist one of the counter-rotating vortices and leaves the other straight. The convergence of the modes are investigated and it is shown that approximately the same number of snapshots are needed for both trains. 

  • 66.
    Muld, Tomas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mode Decomposition on Surface-Mounted Cube2012Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 88, nr 3, s. 279-310Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the flow around the surface-mounted cube is decomposed into modes using Proper Orthogonal Decomposition (POD) and Koopman mode decomposition, respectively. The objective of the paper is twofold. Firstly, a comparison of the two decomposition methods for a highly separated flow is performed. Secondly, an evaluation of Detached Eddy Simulation (DES) for simulating a time-accurate flow, to be used as input data for the two mode decomposition methods, is accomplished. The knowledge on the accuracy and usefulness of the modes computed with from DES flow fields can then be the foundation for other studies for applied geometries in vehicle aerodynamics. The flow is simulated using DES, which enables time-accurate simulations on flows around realistic vehicle geometries. Most of the first eight modes computed with DES in a reference domain can also be found among the first eight computed with LES in reference work. Since the POD modes computed with DES resemble those computed with LES, the conclusion is that DES is suitable to use for mode decomposition. When comparing the POD and Koopman modes, many similarities can be found in both the spatial and temporal modes. For this case, where the flow contains a broad band of frequencies, it is concluded that the advantage of using Koopman modes, decomposing by frequency, cannot be fully utilized, and Koopman modes are very similar to the POD modes.

  • 67.
    Muld, Tomas W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow structures around a high-speed train extracted using Proper Orthogonal Decomposition and Dynamic Mode Decomposition2012Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 57, s. 87-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to extract the most dominant flow structures of a simulated flow in the wake of a high-speed train model, the Aerodynamic Train Model (ATM). The use of decomposition methods to successfully identify dominant flow structures for an engineering geometry is achieved by using a flow field simulated with the Detached Eddy Simulation model (DES), which is a turbulence model enabling time accurate solutions of the flows around engineering geometries. This paper also examines the convergence of the POD and DMD modes for this case. It is found that the most dominant DMD mode needs a longer sample time to converge than the most dominant POD mode. A comparison between the modes from the two different decomposition methods shows that the second and third POD modes correspond to the same flow structure as the second DMD mode. This is confirmed both by investigating the spectral content of the POD mode coefficients, and by comparing the spatial modes. The flow structure associated with these modes is identified as being vortex shedding. The identification is performed by reconstructing the flow field using the mean flow and the second DMD mode. A second flow structure, a bending of the counter-rotating vortices, is also identified. Identifying this flow structure is achieved by reconstructing the flow field with the mean flow and the fourth and fifth POD modes.

  • 68.
    Muld, Tomas W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mode Decomposition and Slipstream Velocities in the Wake of Two High-Speed Trains2012Ingår i: The international Journal of railway technology, ISSN 2049-5358, E-ISSN 2053-602X, The International Journal of Railway TechnologyArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Two different train geometries, the Aerodynamic Train Model (ATM) and the CRH1, are studied in order to compare the flow fields around the trains. This paper focuses on the flow structures and flow topologies in the wake. The flow is simulated with Detached Eddy Simulation and decomposed into modes with Proper Orthogonal Decomposition and Dynamic Mode Decomposition, respectively. The topology of the flow is found to be different for the two train geometries, where the flow behind the ATM separates with two counter-rotating vortices, while the flow behind the CRH1 separates with a separation bubble. The difference in flow topology is seen, for instance,  in the mean pressure at the tail, the mean flow in the wake and streamlines of the flow. Despite the different flow topology, there are also similar flow structures in the wake behind the ATM and the CRH1, such as vortex shedding. In order to measure the slipstream effect of the two vehicles, the velocity in a ground fixed point has to be extracted from the train fixed flow field. The resulting velocity is averaged with an equivalent of 1s time average at full scale. The contribution of the DMD modes to slipstream has been analyzed and it is found that the same flow structure that is dominant in energy is also important for slipstream.

  • 69.
    Muld, Tomas W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Proper orthogonal decomposition of flow structures around a surface-mounted cube computed with detached-eddy simulation2009Ingår i: SAE World Congress & Exhibition, 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper the flow passing a cube mounted in a channel is studied via detached-eddy simulation (DES). The results are compared to previous studies, where large eddy simulation (LES) have been used. The mean velocity profile found in this paper was found to match with other references above the cube but not behind the cube. The shear stress was underpredicted by the DES computations on top of the cube. Behind the cube the LES and experimental studies show a much more smeared shear layer than the DES calculation. The proper orthogonal decomposition (POD) modes are calculated and investigated. The first mode, which corresponds to the mean flow, was found to contain the flow structure of the large separation above the cube. The POD modes calculated from the DES results show higher percentage of energy in the first mode than the POD calculated from LES results.

  • 70.
    Muld, Tomas W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wake characteristics of high-speed trains with different lengths2014Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, nr 4, s. 333-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three different train configurations with different numbers of cars are analysed in order to investigate the effect of the train length on wake structures. The train geometry considered is the aerodynamic train model and the different versions have two, three and four cars. Due to the different lengths of the trains, the boundary-layer thickness will be different at the tail of each configuration. The flow is simulated using detached eddy simulation, and coherent flow structures are extracted via proper orthogonal decomposition and dynamic mode decomposition. As a result of reconstruction of the flow field using coupling of the mean flow and the first fluctuating proper orthogonal decomposition mode, it is found that the dominant flow structure in the wake is the same for all three cases. However, this structure has different frequencies and wavelengths depending on the boundary-layer thickness in front of the separation. It is shown that the frequency decreases as the boundary-layer thickness increases for these train configurations.

  • 71.
    Muld, Tomas W.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Herbst, Astrid H.
    Bombardier Transportation, Sweden.
    Orellano, Alexander
    Bombardier Transportation, Sweden.
    Analysis of flow structures in the wake of a high-speed train2016Ingår i: Proceedings aerodynamics of heavy vehicles III, buses, trucks and trains, Springer, 2016, Vol. 79Konferensbidrag (Refereegranskat)
    Abstract [en]

    Slipstream is the flow that a train pulls along due to the viscosity of the fluid. In real life applications, the effect of the slipstream flow is a safety concern for people on platform, tracksideworkers and objects on platforms such as baggage carts and pushchairs. The most important region for slipstream of high-speed passanger trains is the near wake, in which the flow is fully turbulent with a broad range of length and time scales. In this work, the flow around the Aerodynamic Train Model (ATM) is simulated using Detached Eddy Simulation (DES) to model the turbulence. Different grids are used in order to prove grid converged results. In order to compare with the results of experimental work performed at DLR on the ATM, where a trip wire was attached to the model, it turned out to be necessary to model this wire to have comparable results. An attempt to model the effect of the trip wire via volume forces improved the results but we were not successful at reproducing the full velocity profiles. The flow is analyzed by computing the POD and Koopman modes. The structures in the floware found to be associated with two counter rotating vortices. A strong connection between pairs of modes is found, which is related to the propagation of flow structures for the POD modes. Koopman modes and POD modes are similar in the spatial structure and similarities in frequencies of the time evolution of the structures are also found.

  • 72.
    Na, Wei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Acoustic characterization of a hybrid liner consisting of porous material by using a unified linearized navier-stokes approach2016Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics, 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 73.
    Na, Wei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Simulations of acoustic wave propagation in an impedance tube using a frequency-domain linearized navier-stokes methodology2014Ingår i: 20th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 74.
    Na, Wei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Numerical prediction of thermoacoustic instabilities with a V-Flame2016Ingår i: 23rd International Congress on Sound and Vibration 2016 (ICSV 23), Athens, Greece 10-14 July 2016, Volume 1 of 6: From Ancient to Modern Acoustics, International Institute of Acoustics and Vibrations , 2016, Vol. 1Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 75.
    Na, Wei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Prediction of thermoacoustic instabilities in combustors using linearized Navier-Stokes equations in frequency domain2015Ingår i: 22nd International Congress on Sound and Vibration, ICSV 2015, Vol. 2 / [ed] Malcolm J. Crocker ; Francesca Pedrielli ; Sergio Luzzi ; Marek Pawelczyk ; Eleonora Carletti, International Institute of Acoustics and Vibrations , 2015, Vol. 2, s. 2011-2018Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 76.
    Na, Wei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Simulations of the scattering of sound waves at a sudden area expansion in a 3D duct2014Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014, international Institute of Acoustics and Vibrations , 2014, Vol. 1, s. 1420-1427Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 77.
    Nair, Vineeth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alenius, Emma
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Inspecting sound sources in an orifice-jet flow using Lagrangian coherent structures2016Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 140, s. 397-405Artikel i tidskrift (Refereegranskat)
    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.

  • 78.
    O'Reilly, Ciarán J.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alenius, Emma
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, 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 flow2012Ingår i: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 79.
    O'Reilly, Ciarán J.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alenius, Emma
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, 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 flow2011Ingår i: 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), 2011Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 80.
    O'Reilly, Ciarán J.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hammar, Johan
    Creo Dynamics AB.
    Emborg, Urban
    Creo Dynamics, Sweden.
    Numerical investigation of self-sustained shock oscillation acoustics2012Ingår i: 10th International Conference on Flow-Induced Vibration and Flow-Induced Noise, FIV / [ed] Meskell & Bennett, FIV , 2012, s. 681-688Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A numerical investigation of the sound resultant from a compressible flow about an 18% thick circular-arc aerofoil, for free-stream Mach numbers between M = 0.7 and M = 0.82, and a Reynolds number Re ~ 10^7, is presented in this paper. Within this range of parameters, self-sustained shock oscillations may be present on the upper and lower aerofoil surfaces. The transient flow-field was computed by detached-eddy simulation, with the solution used to quantify acoustic sources, defined by Howe's analogy, that are propagated using a wave expansion method. The results were compared with available experimental and numerical results from other studies of the same configuration.

  • 81.
    O'Reilly, Ciarán J.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hammar, Johan
    Creo Dynamics, Sweden.
    Emborg, Urban
    Creo Dynamics, Sweden.
    Persson, Andreas
    Creo Dynamics, Sweden.
    An Investigation into Shock Oscillation Noise Reduction2013Ingår i: 4th CEAS Air and Space Conference, 2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Self-sustained shock-oscillations were investigated in this work, with a view to implementing countermeasures to stop the motion of the shock and, therefore, to reduce the associated noise. The transonic flow past a symmetric airfoil was computed using computational fluid dynamics. A number of potential countermeasures were also included in the simulations in order identify the relative importance of their physical parameters in reducing the shock motion. 

  • 82.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Botha, Jason D. M.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Karl, Bolin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    O'Reilly, Ciarán J.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Rice, Henry J.
    Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
    Aerodynamic noise prediction for a wind turbine using numerical flow simulations and semi-empirical modelling approaches2016Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, aerodynamic and aero-acoustic simulations are performed for a small horizontal axis wind turbine, suitable for the integration of wind energy in urban and peri-urban areas. Detached-eddy simulation (DES) of compressible flow is performed to compute the flow field over the wind turbine. The far-field noise is computed using the Ffowcs - Williams and Hawkings acoustic analogy. Furthermore, the blade element momentum theory is used with a semi-empirical acoustic modeling approach to predict the wind turbine noise. The acoustic modeling approach is based on a semi-empirical formulation for airfoil self noise and an analytic formulation for inflow noise.

  • 83.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Chevalier, M.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    A numerical study of noise characteristics originating from a shrouded subsonic automotive fan2018Ingår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 140, s. 110-121Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The characteristics of the noise radiated from a reduced automotive cooling module are numerically studied focusing on the interaction effects linked to the sound generation mechanisms and the acoustic scattering caused by the confined installation. The flow field is simulated by adopting the formulation of Improved Delayed Detached Eddy Simulation (IDDES), which is a numerical technique that enables large-scale structures to be resolved and the wall-bounded flow to be treated depending on the turbulent content within the boundary layer. By comparing the simulated fan performance to two sets of measurement data of a similar setup, the aerodynamic results obtained from IDDES are validated and conformed to the volumetric flow rate delivered for the pressure drop measured. The acoustic part of the study comprises evaluation of the sound source associated with the momentum distribution imposed on the surroundings at an interface slightly upstream of the fan. At the microphone positions upstream of the installation, the SPL falls within the SPL range measured and the acoustic power delivered by the fan conforms to the SWL obtained from the comparison method in the reverberation room. The system response function, estimated by subtracting the SWL for the free-field simulation from the SWL associated with the reduced automotive cooling module marks spectral humps at fixed frequencies, irrespectively of sound source. As such, the engineering approach to the spectral decomposition method earlier published, which enables the acoustical properties of the installation to be isolated from the source, is validated and found to hold.

  • 84.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, M.
    Scania AB, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Vibrationsövervakning.
    Acoustic characteristics of a heavy duty vehicle cooling module2016Ingår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 111, s. 67-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.

  • 85.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic characteristics of a heavy duty vehicle cooling moduleManuskript (preprint) (Övrigt vetenskapligt)
  • 86.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustical Broadband signatures from RANS Turbulence Quantities2014Ingår i: The 21st International Congress on Sound and Vibration, 2014, s. 1541-1548Konferensbidrag (Refereegranskat)
    Abstract [en]

    The high capacity of today's computers open up the possibility of using numerical simulations to provide a reliable support for optimization of the cooling module placed in heavy vehicles from both an acoustical and aerodynamic perspective. Typically the cooling compartment in heavy trucks consists of a large number of components building a complex, geometrically dense, package. Acoustically, adjacent surfaces are known to modify the sound level and the sound directivity caused mainly by the fan. For this reason, prediction of the sound sources and their radiation, using highly resolved turbulent numerical simulations, is still not feasible. In this paper, we present acoustic predictions that are based on results from Reynolds-Averaged Navier-Stokes (RANS) simulations on a given fan setup with the objective to identify noise characteristics from the turbulent quantities, using analytical expressions derived for isolated airfoils. The analytical formulas give the power spectral density (PSD) in the far-field associated with the noise mechanisms known as incoming turbulence noise and trailing edge noise both caused by the scattering of turbulent structures at the airfoil's leading- and trailing edge, respectively. In the fan setup, the fan was closely mounted to a shroud and placed in a wall between two adjacent rooms. Compared to the intricate underhood engine bay in a truck, the surrounding area affecting the acoustic radiation has been heavily reduced. Emphasis is to seize the apparent broadband trends previously measured in a facility customized for acoustical investigations. The fan studied is running at subsonic speed and consists of 11 blades, having a diameter of 0.75 m. The sound pressure level (SPL) calculated using the analytical expressions was found to show broadband properties previously captured during measurements.

  • 87.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Aeroacoustic calculation using DES together with FW-H for a ducted subsonic fan2014Rapport (Övrigt vetenskapligt)
  • 88.
    Rynell, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, Mattias
    Scania CV, Sweden.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Quiet and efficient cooling for IC-engine powered systems2013Ingår i: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life, OAL-Osterreichischer Arbeitsring fur Larmbekampfung , 2013, s. 5677-5686Konferensbidrag (Refereegranskat)
    Abstract [en]

    The cooling module placed in heavy vehicles is a compact installation, consisting of several components that all affect the cooling air stream which results in complex flows. Even though the fan is considered the main source of sound, adjacent surfaces affect the flow and the scattering of the sound radiated from the fan and make it difficult to predict the acoustic source distribution and sound field inside and outside of the cooling system. This paper focus on the noise emissions caused by the flow associated with the cooling fan and the interaction with an upstream radiator. The long- Term objective of the work is to obtain an efficient and accurate simulation tool for the design of silent and efficient cooling systems, where the present work will be a viable tool in the evaluation process. A modular test rig was built that consisted of a radiator, shroud, fan and hydraulic engine mounted in a wall, which was located between an anechoic room and a reverberation room in order to control the sound level of the incoming flow. Acoustic characteristics e.g. sound pressure- And sound power levels, have been measured in both rooms and will later be used to validate future numerical simulations.

  • 89.
    Sack, Stefan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    On Acoustic Multi-Port Characterisation Including Higher Order Modes2016Ingår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 192, nr 5, s. 834-850Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methods to design test-procedures for acoustic multi-ports in ducts with a focus on pressure sampling positions for accurate modal decomposition are demonstrated. Acoustic fields up- and downstream of an in-duct acoustic element are excited by external sources and decomposed into transmitted and reflected aeroacoustic modal pres- sure amplitudes in order to first determine the acoustic scattering of the element. Secondly, the determination of the element source strength requires tests with no external sources, but with known terminations and scattering data. Unfavourable source and sensor positions lead to mode coupling and to ill-conditioned or even singular decomposition matrices, which results in high amplifications of uncertainties within the wave decomposition. An unoptimised but over-determined assembly is compared with a setup containing a minimum of sensors but with optimised positions. Lower uncertainty amplification, despite the usage of fewer sensors, is achieved for most frequencies, especially after the cut-on of t he higher order acoustic modes. A genetic algorithm (GA) is used to achieve this optimised setup by minimising the condition number of the decomposition matrix, which is a multi-dimensional optimisation problem with numerous local minima. To estimate the stability of the optimised configuration, a Monte-Carlo Method (MCM) is deployed to introduce normal distributed complex pressure un- certainties into the decomposition. In order to estimate the wave number, different approaches are compared - namely the classical non-dissipative wav e number estimate, an extended Kirchhoff method for viscous-thermal damping and an eigenvalue solution of the Linearised Navier Stokes Equations by Dokumaci. The presented de- composition method is not only applicable to measurement data but is equally useful to post-process results from numerical computation.

  • 90.
    Siklosi, Malin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik.
    Analysis of first order errors in shock calculations in two space dimensions2005Ingår i: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 43, nr 2, s. 672-685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical computations show that solutions of hyperbolic conservation laws obtained by second or higher order shock capturing methods in many cases are only first order accurate downstream of shocks (see, e.g., [M. H. Carpenter and J.H. Casper, AIAA J., 37 (1999), pp. 1072 1079]). We use matched asymptotic expansions to analyze the degeneration in order of accuracy for stationary solutions of hyperbolic conservation laws in two space dimensions.

  • 91.
    Stensson Trigell, Annika
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
    Jerrelind, Jenny
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Numerisk akustik.
    ECO2 Vehicle Design: an initiative for a holistic perspective on future vehicle concepts2008Konferensbidrag (Övrigt vetenskapligt)
  • 92.
    Temiz, M. A.
    et al.
    Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, The Netherlands.
    Arteaga, I. L.
    Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, The Netherlands.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Hirschberg, A.
    Eindhoven University of Technology, Department of Applied Physics, Eindhoven, The Netherlands,.
    Acoustic end correction in micro-perforated plates - Revisited2014Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, s. 1203-1209Konferensbidrag (Refereegranskat)
    Abstract [en]

    Micro-Perforated plates (MPP) are plates with a porosity of the order of 1% in which the perforation diameter is optimized for absorption of incident acoustic waves. The concept has been introduced by Maa[1], who proposed an analytical model based on the solution for the oscillating viscous flow in a long capillary tube. The finite length of the geometry is taken into account by reactive and resistive end-corrections of Ingard[2]. In order to match experimental data, the single sided resistive end correction of Ingard has been multiplied by a factor a. This factor varies in the literature in the range 2 ≤ α ≤ 4. Bolton and Kim[3] propose the use of CFD to determine these end-corrections. Using a similar approach, our present work proposes an alternative result to their work. We use a linear numerical model based on incompressible Navier-Stokes equations in 2D-axisymmetric coordinates, which is solved in the Fourier domain, rather than the time domain simulation as proposed by Bolton and Kim. Working in the Fourier domain with linearized equations ensures the numerical efficiency and absence of non-linear effects. We furthermore use an alternative procedure to determine the inertial part of the transfer impedance leading to a difference of the order of 10% with the results of Bolton and Kim. Moreover, our results show that resistive and reactive end corrections are mainly a function of the Shear number Sh. The porosity a and plate thickness to perforation diameter ratio t∗ seems to be less important.

  • 93.
    Temiz, Muttalip Askin
    et al.
    Eindhoven University of Technology, Department of Mechanical Engineering, Dynamics and Control, The Netherlands.
    Arteaga, Ines Lopez
    Eindhoven University of Technology, Department of Mechanical Engineering, Dynamics and Control, The Netherlands.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Hirschberg, Avraham
    Eindhoven University of Technology, Department of Applied Physics, Gas Dynamics and Aero-Acoustics, The Netherlands.
    The influence of edge geometry on end-correction coefficients in micro perforated plates2015Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 138, nr 6, s. 3668-3677Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Global expressions are proposed for end-correction coefficients in micro perforated plates (MPPs) using non-dimensional parameters. MPPs are sound absorbers with small perforation diameters such that the Stokes boundary layers fill up almost the entire perforation. Sound absorption does not only occur within the perforation, but also takes place just outside of it. The latter contribution plus the outside inertia effect on the transfer impedance of the MPP are referred to as end-corrections. In order to determine them, an analytical solution employing the very thin Stokes layer assumption has been derived. However, this assumption requires empirical coefficients in the end-corrections for accurate results. To explore the effects of various parameters a numerical model is used. This model is verified with open-end reflection coefficient measurements. The most prominent result from this study is that compared to plate thickness, the ratio of perforation diameter to Stokes layer thickness (Shear number) and edge geometry affect the end-correction coefficients more significantly. The effect of plate thickness can be neglected for practical purposes, therefore, expressions for the end-corrections in terms of Shear number and edge geometry are provided. The relative error of these expressions is <3% compared to the numerical results. 

  • 94.
    Tyskeng, Sara
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Numerisk akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Ecological and economical Critera in Vehicle Design: Taking on the challenge2009Ingår i: Public Service Review: European Union, nr 19Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 95.
    Tyskeng, Sara
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Jerrelind, Jenny
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aeroakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Wennhage, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Numerisk akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Centre for ECO2 Vehicle Design: vehicle design research for more environmentally friendly and economically competitive vehicles2008Ingår i: The Vehicle Component, SVENartikelArtikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 96.
    Winkler, Niklas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Drugge, Lars
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Stensson Trigell, Annika
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Aerodynamics of road vehicles in transient cross-winds-coupling aero to vehicle dynamics2014Ingår i: Proceedings of the Mini Conference on Vehicle System Dynamics, Identification and Anomalies, Technical University of Budapest , 2014, s. 63-70Konferensbidrag (Refereegranskat)
    Abstract [en]

    Ground vehicles are sensitive to crosswinds, affecting aerodynamic and handling performance, and in some cases safety. Therefore it is important to be able to predict vehicle performance when exposed to crosswinds. The aim of the work presented in this paper is to assess the order of the model complexity in order to capture the vehicle behaviour during a transient crosswind event, regarding the interaction of the aerodynamic forces and the vehicle dynamic response. That is, the necessity to perform a full dynamic coupling instead of a static coupling to capture the vehicle performance both with respect to aerodynamics and the vehicle dynamics as is done today. The model used in the computations is based on the Ground Transportation System (GTS) model, which is simulated to run on a road passing a crosswind passage. The aerodynamic computations are performed using Detached Eddy Simulation (DES) coupled to a bicycle model for the vehicle dynamics. Here, two degrees of freedom are considered, that is, lateral translation and yaw motion. The change of the vehicle position in the aerodynamic domain is enabled through the use of the overset mesh technique. The results show that the full dynamic coupling is needed for large yaw angles of the vehicle, where the static coupling over-predicts the aerodynamic loads and in turn the vehicle motion.

  • 97.
    Winkler, Niklas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Drugge, Lars
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Stensson Trigell, Annika
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Coupling aerodynamics to vehicle dynamics in transient crosswinds including a driver model2016Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 138, s. 26-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we assess the order of model complexity needed to capture a vehicle behaviour during a transient crosswind event, regarding the interaction of the aerodynamic loads and the vehicle dynamic response. The necessity to perform a full dynamic coupling, including feedback in real-time, instead of a static coupling to capture the vehicle performance both with respect to aerodynamics and the vehicle dynamics is evaluated. The computations are performed for a simplified bus model that is exposed to a transient crosswind. The aerodynamic loads are obtained using Detached Eddy Simulation (DES) with the overset mesh technique coupled to a single-track model for the vehicle dynamics including a driver model with three sets of controller parameters to obtain a realistic scenario. Two degrees of freedom are handled by the vehicle dynamics model; lateral translation and yaw motion. The results show that the full dynamic coupling is needed for large yaw angles of the vehicle, where the static coupling over-predicts the aerodynamic loads and in turn the vehicle motion. © 2016 Elsevier Ltd

12 51 - 97 av 97
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf