Change search
Refine search result
1 - 34 of 34
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Chevrolat, Sofia
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Automatic Fusion of Fidelity sources ofAerodynamic Data: Simulating Aircraft Stability And Control Characteristics for Use in Conceptual Design2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    CFD use has increased signi cantly in airplane conception, and the industry demands more andmore precise and reliable tools. This was the goal of the SimSAC project. The result is CEASIOM,a computerized environment made of several modules for the design and prediction of the aircraft'scharacteristics. It constructs aerodynamic tables used in the prediction of the characteristics of anaircraft. In simple ight conditions, simple computation methods are used, whereas in complex ightconditions,involving turbulences, more advanced methods are used. This reduces the computationalcost, but the tables resulting from di erent delity sources must be fused to obtain a coherent tablecovering the whole ight envelope.The goal of this project was to realize the fusion. Additionally, a lter and a custom-made mapping toenhance the accuracy of the results from the fusion were required. The addition of helpful visualizationtools was suggested. The whole should be integrated in the CEASIOM interface as a Fusion module.For this, 6 functions were coded. The rst one loads the data sets. The second, myplot, allows theengineer by plotting the data in a coherent way, to spot any big mistakes or incompatibility in thedata sets. The third, myvisual, displays the elements spotted as outliers or potentially out of pattern.This is used by the next function, my ltermap, to lter out the erroneous data. This function alsorealizes the custom-made mapping.The fth function, myfusion, fuses the data and saves it in a .xmlCEASIOM formatted structure to be used by the next CEASIOM module. The sixth function ltersout, in the same way as my ltermap, the outliers from the fused data, and saves the ltered fused dataset in a .xml CEASIOM formatted structure. Finally, a Matlab GUI was implemented and integratedinto the main CEASIOM interface.The module works perfectly, except for the mapping part, that needs a few readjustments.

  • 2.
    Divaret, Lise
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    U-RANS Simulation of fluid forces exerted upon an oscillating tube array2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this master thesis is to characterize the fluid forces applied to a fuel assembly inthe core of a nuclear power plant in case of seism. The forces are studied with a simplifiedtwo-dimensional model constituted of an array of 3 by 3 infinite cylinders oscillating in aclosed box. The axial flow of water, which convects the heat in the core of a nuclear powerplant, is also taken into account. The velocity of the axial flow reaches 4m/s in the middle ofthe assembly and modifies the forces features when the cylinders move laterally.The seism is modeled as a lateral displacement with high amplitude (several cylinderdiameters) and low frequencies (below 20 Hz). In order to study the effects of the amplitudeand of the frequency of the displacement, the displacement taken is a sine function withboth controlled amplitude and frequency. Four degrees of freedom of the system will bestudied: the amplitude of the displacement, its frequency, the axial velocity amplitude andthe confinement (due to the closed box).The fluid forces exerted on the cylinders can be seen as a combination of three terms: anadded mass, related to the acceleration of cylinders, a drift force, related to the damping ofthe fluid and a force due to the interaction of the cylinder with residual vortices. The firsttwo components will be characterized through the Morison expansion, and their evolutionwith the variation of the degree of freedom of the system will be quantified. The effect ofthe interaction with the residual vortices will be observed in the plots of the forces vs. timebut also in the velocity and vorticity map of the fluid.The fluid forces are calculated with the CFD code Code_Saturne, which uses a second orderaccurate finite volume method. Unsteady Reynolds Averaged Navier Stokes simulations arerealized with a k-epsilon turbulence model. The Arbitrary Lagrange Euler model is used todescribe the structure displacement. The domain is meshed with hexahedra with thesoftware gmsh [1] and the flow is visualized with Paraview [2]. The modeling techniquesused for the simulations are described in the first part of this master thesis.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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)
  • 6.
    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.

  • 7.
    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)
  • 8.
    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.

  • 9.
    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.

  • 10.
    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.

  • 11.
    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)
  • 12.
    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)
  • 13.
    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)
  • 14.
    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)
  • 15.
    Gottfarb Bart, Samuel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Optimal placement of plasma actuators on trucks: A drag reduction study using adjoint methods2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The fuel consumption of vehicles plays an important environmental role and ways of improving the fuel economy is beneficial for a sustainable future. Active flow control is one method that can potentially reduce the aerodynamic drag significantly and therefore the fuel consumption. A plasma actuator introduces momentum in its vicinity and can be used for active control of the flow.

    This thesis aimed to find the optimal placement of plasma actuators on the A-pillars of a truck, using Reynolds-Averaged Navier-Stokes (RANS) simulations performed with STAR-CCM+. The adjoint solver was used to obtain a sensitivity map of the drag with respect to the variation of momentum. This was then used when the accuracy of this adjoint solution was evaluated by performing parametric studies where the actuation was placed at different locations around the point of flow separation.

    A simple case consisting in a half-submerged cylinder was first studied as both wind tunnel experiments and Large Eddy Simulations (LES) have been previously performed on this flow case at KTH. When placing actuation on top of the cylinder, the drag reduction obtained with RANS was 4.3% which was comparable to the previous LES work, where the reduction was 4.65%. With the flow separating at 98 degrees in a local cylindrical coordinate system, which starts at the leading edge of the cylinder, the adjoint solution showed that the optimal placement was located at 105 degrees. The actuation was placed at several locations between 90 and 118 degrees and the minimum was found to be located at 106 degrees.

    The Ground Transportation System (GTS) model representing a generic tractor-trailer combi-nation, both in two and three dimensions, was then used with the same solution procedure. In the two-dimensional case, the flow was found to separate at 63 degrees. The optimal placement predicted by the adjoint solver was 69 degrees, while the parametric study showed the optimal location to be at 75 degrees. The added complexity of an extra dimension resulted in the wind speed having to be lowered in order to produce similar results for the actuation. However, agreement on the optimal location was observed between the two- and three-dimensional cases.

    In general, the adjoint solver showed varying levels of accuracy between simulations, but still gave a qualitative indication of the optimal placement. A correlation between the point of separation of the flow and the adjoint solution was observed and along with the results from the parametric studies, the optimal placement was concluded to be slightly downstream of the separation point. In order to obtain the exact optimal position, a parametric study is needed for each individual case.

  • 16.
    Kierkegaard, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Traffic is a major source of environmental noise in modern day's society. As a result, the development of new vehicles are subject to heavy governmental legislations. The major noise sources on common road vehicles are engine noise, transmission noise, tire noise and, at high speeds, wind noise. One way to reduce intake and exhaust noise is to attach mufflers to the exhaust pipes. However, to develop prototypes for the evaluation of muffler performance is a costly and time-consuming process. As a consequence, in recent years so called virtual prototyping has emerged as an alternative. Current industrial simulation methodologies are often rather crude, normally only including one-dimensional mean flows and one-dimensional acoustic fields. Also, flow generated noise is rudimentary modeled or not included at all. Hence, improved methods are needed to fully benefit from the possibilities of virtual prototyping.

    This thesis 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. Special focus has been at investigating the possibilities to use frequency-domain linearized Navier-Stokes equations solvers, where the equations are solved either directly or as eigenvalue formulations.

    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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)
  • 20.
    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.

  • 21.
    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)
  • 22.
    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.

  • 23.
    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.

  • 24.
    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)
  • 25.
    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.

  • 26.
    Kårekull, Oscar
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Fläkt Woods, Jönköping, Sweden .
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Comparison of RANS parameters for flow noise prediction2013In: 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, p. 5916-5925Conference paper (Refereed)
    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.

  • 27.
    Muld, Tomas W.
    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, Linné Flow Center, FLOW.
    Henningson, Dan S
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Flow structures around a high-speed train extracted using Proper Orthogonal Decomposition and Dynamic Mode Decomposition2012In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 57, p. 87-97Article in journal (Refereed)
    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.

  • 28.
    Na, Wei
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. SDB Aerodynamic.
    Frequency Domain Linearized Navier-Stokes Equations Methodology for Aero-Acoustic and Thermoacoustic Simulations2015Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The first part of the thesis focuses on developing a numerical methodology to simulate the acoustic properties of a hybrid liner consisting of a perforated plate, a porous layer and a Helmholtz cavity. Liners are always a standard way to reduce noise in today’s aeroengines, e.g. the fan noise can be reduced effectively through the installation of acoustic liners as wall treatments in the ducts. In order to optimize a liner in the design phase, an accurate and efficient prediction tool is of interests. Hence, a unified Linearized Navier-Stokes equations(LNSE) approach has been implemented in the thesis, combining the LNSE in frequency domain with the fluid equivalent model. The LNSE is applied in the vicinity of the perforated plate to simulate sound propagation including viscous damping effect, and the fluid equivalent model is used to model the sound propagation in the porous material including absorption.

    The second part of the thesis focuses on the prediction of thermoacoustic instabilities. Thermoacoustic instabilities arise when positive coupling occurs between the flame and the acoustics in the feedback loop, i.e. the flame acts as an amplifier of the disturbances (acoustic or fluid) at a natural frequency of the combustion system. Once the thermoacoustic instabilities occur, it will lead to extremely high noise levels within a relatively narrow frequency range, resulting in a huge damage to the structure of the combustors. Hence, a solution must be found, which breaks the link between the combustion process and the structural acoustics. The numerical prediction of thermoacoustic instabilities in the thesis is performed by two different numerical methodologies. One solves the Helmholtz equation in combination of the flame n − tau model with the low Mach number assumptions, and the other solves the Linearized Navier-Stokes equations in frequency domain with mean flow. The result show that the mean flow has a significant effect on the thermoacoustic instabilities, which is non-negligible when the Mach number reaches to 0.15.

  • 29.
    O'Reilly, Ciarán J.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rice, Henry J.
    Trinity College, Dublin, Ireland.
    A Lighthill based jet noise model for acoustic shielding prediction2010In: 17th International Congress on Sound and Vibration, ICSV17: Volume 1, 2010, p. 558-565Conference paper (Other academic)
    Abstract [en]

    The majority of research on jet noise has considered isolated shear-flows and, as such, jet noise models based on Lighthill's acoustic analogy traditionally assume a free-space Green's function for propagation. In order to evaluate the reduction in jet noise attainable from proposed airframe shielding configurations, a jet noise model based on Lighthill's analogy is derived in this paper, which retains an explicit Green's function in the expression for the far-field spectral density. This Green's function may be evaluated to include the diffraction of the sound field about an acoustic shield. A preliminary comparison is made with the limited data available for shielded jets. In addition to facilitating the study of shielding configurations, isolated predictions made using this model compare favourably with isolated jet noise data.

  • 30.
    O'Reilly, Ciarán J.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Rice, Henry J.
    Trinity College, Dublin, Ireland.
    Investigation of a jet-noise-shielding methodology2015In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 53, no 11, p. 3286-3296Article in journal (Refereed)
    Abstract [en]

    Ongoing research toward the reduction of environmental noise from aircraft is investigating the possible shielding of engine-noise sources by novel airframe configurations. To assess the noise-reduction benefits attainable from such configurations, it is necessary to develop appropriate acoustic evaluation tools. In this paper, a jet-noise-shielding- prediction methodology is described. The Tam–Auriault (“Jet Mixing Noise from Fine-Scale Turbulence,” AIAA Journal, Vol. 37, No. 2, 1999, pp. 145–153) jet-noise model with a Reynolds-averaged Navier–Stokes solution input, together with a Fresnel–Kirchhoff diffraction method (Fundamentals of Physical Acoustics, Wiley-Interscience, New York, 2000, pp. 472–494), is used to make isolated and shielded far-field jet-noise predictions. This methodology is employed as a sensitivity-analysis tool to establish the relative importance of the source location, spatial extent, and directivity in jet-noise-shielding predictions. Predictions have been made for a shielded single-stream Mach 0.9 jet, and compared with experimental data. Good qualitative agreement is observed, and the disagreement in the shielding levels is most likely due to underestimation of the source axial extent by the jet-noise model. 

  • 31.
    Sedarati, Parinaz
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Simulations of sound propagation at a duct termination with flow2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Both theoretically as well as in many applications like exhaust systems, ventilation pipes, mufflers, air intakes and also large scale industrial smoke stacks, it is of interest to understand how sound waves are scattered at duct exists. Especially for aeronautical application such as jet engines, the effect of coupling of acoustics and flow on sound radiation and reflection from a duct termination in a uniform is an important problem. In order to predict the acoustic performance in duct systems, it is essential to know how the incoming acoustic waves are propagated and transmitted and reflected. This thesis work aims at developing suitable simulation methods as extension to existing software and to validate these methods to experimental measurements and theory. Firstly, numerical simulations of fully developed flow through a duct exit has been carried out. The goal in this part is to obtain the mean values for the velocity and pressure. The commercial code Fluent 12.1 is used for numerical simulations in two space dimensions. Secondly, numerical simulations of the acoustic part has been studied with the commercial software Comsol 3.5a with the objective to investigate the ability of the frequency domain Navier-Stokes equations to the characteristic properties of the acoustics at the duct termination. Finally, numerical results are compared to available experimental results with acceptable agreement which shows successes and also constraints of the simulations.

  • 32.
    Siklosi, Malin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics.
    Analysis of first order errors in shock calculations in two space dimensions2005In: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 43, no 2, p. 672-685Article in journal (Refereed)
    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.

  • 33.
    Tyskeng, Sara
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies. 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), 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.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Ecological and economical Critera in Vehicle Design: Taking on the challenge2009In: Public Service Review: European Union, no 19Article in journal (Other (popular science, discussion, etc.))
  • 34.
    Tyskeng, Sara
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies. 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, Vehicle Dynamics. 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), 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.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Centre for ECO2 Vehicle Design: vehicle design research for more environmentally friendly and economically competitive vehicles2008In: The Vehicle Component, SVENartikelArticle in journal (Other (popular science, discussion, etc.))
1 - 34 of 34
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf