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Publications (10 of 15) Show all publications
Hodzic, E., Alenius, E., Duwig, C., Szasz, R. S. & Fuchs, L. (2017). A Large Eddy Simulation Study of Bluff Body Flame Dynamics Approaching Blow-Off. Combustion Science and Technology, 189(7), 1107-1137
Open this publication in new window or tab >>A Large Eddy Simulation Study of Bluff Body Flame Dynamics Approaching Blow-Off
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2017 (English)In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 189, no 7, p. 1107-1137Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
Taylor & Francis, 2017
Keywords
Blowoff (BO), Bluff body flame (BBF), Flame dynamics, Large eddy simulation (LES), Proper orthogonal decomposition (POD)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-205531 (URN)10.1080/00102202.2016.1275592 (DOI)000398229600002 ()2-s2.0-85034628519 (Scopus ID)
Note

QC 20170509

Available from: 2017-05-09 Created: 2017-05-09 Last updated: 2017-05-09Bibliographically approved
Nair, V., Alenius, E., Boij, S. & Efraimsson, G. (2016). Inspecting sound sources in an orifice-jet flow using Lagrangian coherent structures. Computers & Fluids, 140, 397-405
Open this publication in new window or tab >>Inspecting sound sources in an orifice-jet flow using Lagrangian coherent structures
2016 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 140, p. 397-405Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Aeroacoustics, Large eddy simulation (LES), Lagrangian coherent structures (LCS), Finite time Lyapunov exponents (FTLE), Dynamic mode decomposition (DMD)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-197766 (URN)10.1016/j.compfluid.2016.09.001 (DOI)000388048400032 ()2-s2.0-84992663769 (Scopus ID)
Note

QC 20161229

Available from: 2016-12-29 Created: 2016-12-08 Last updated: 2017-06-28Bibliographically approved
Futrzynski, R., Alenius, E. & Efraimsson, G. (2016). Study of Plasma Actuator Efficiency by Simulation of the Detached Flow Over a Half-Cylinder. In: : . Paper presented at 8th AIAA Flow Control Conference. American Institute of Aeronautics and Astronautics
Open this publication in new window or tab >>Study of Plasma Actuator Efficiency by Simulation of the Detached Flow Over a Half-Cylinder
2016 (English)Conference paper, Published paper (Other academic)
Abstract [en]

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

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2016
Keywords
plasma actuator, drag reduction, half-cylinder, LES, plasma model
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-191298 (URN)10.2514/6.2016-4084 (DOI)2-s2.0-84980011713 (Scopus ID)
Conference
8th AIAA Flow Control Conference
Funder
Swedish Energy Agency, 34186-1
Note

QC 20160829

Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2016-11-03Bibliographically approved
Fiorina, B., Mercier, R., Kuenne, G., Ketelheun, A., Avdić, A., Janicka, J., . . . Kempf, A. (2015). Challenging modeling strategies for LES of non-adiabatic turbulent stratified combustion. Combustion and Flame
Open this publication in new window or tab >>Challenging modeling strategies for LES of non-adiabatic turbulent stratified combustion
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2015 (English)In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921Article in journal (Refereed) Published
Abstract [en]

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

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-174712 (URN)10.1016/j.combustflame.2015.07.036 (DOI)000363998300017 ()2-s2.0-84940688872 (Scopus ID)
Note

QC 20151130

Available from: 2015-11-06 Created: 2015-10-07 Last updated: 2017-12-01Bibliographically approved
Alenius, E., Åbom, M. & Fuchs, L. (2015). Large eddy simulations of acoustic-flow interaction at an orifice plate. Journal of Sound and Vibration, 345, 162-177
Open this publication in new window or tab >>Large eddy simulations of acoustic-flow interaction at an orifice plate
2015 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 345, p. 162-177Article in journal (Refereed) Published
Abstract [en]

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

Keywords
aero-acoustics, dynamic mode decomposition, orifice-plate, large eddy simulations
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-161901 (URN)10.1016/j.jsv.2015.02.012 (DOI)000350998800011 ()2-s2.0-84924497139 (Scopus ID)
Note

QC 20150330

Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2017-12-04Bibliographically approved
Carlsson, C., Alenius, E. & Fuchs, L. (2015). Swirl switching in turbulent flow through 90 degrees pipe bends. Physics of fluids, 27(8), Article ID 085112.
Open this publication in new window or tab >>Swirl switching in turbulent flow through 90 degrees pipe bends
2015 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 8, article id 085112Article in journal (Refereed) Published
Abstract [en]

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

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-173986 (URN)10.1063/1.4928971 (DOI)000360646600042 ()2-s2.0-84940399376 (Scopus ID)
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
Note

QC 20151005

Available from: 2015-10-05 Created: 2015-09-24 Last updated: 2017-12-01Bibliographically approved
Alenius, E. (2014). Mode switching in a thick orifice jet, an LES and dynamic mode decomposition approach. Computers & Fluids, 90, 101-112
Open this publication in new window or tab >>Mode switching in a thick orifice jet, an LES and dynamic mode decomposition approach
2014 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 90, p. 101-112Article in journal (Refereed) Published
Abstract [en]

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

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-161902 (URN)10.1016/j.compfluid.2013.11.022 (DOI)000330916000010 ()2-s2.0-84890028616 (Scopus ID)
Note

QC 20150330

Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2017-12-04Bibliographically approved
Alenius, E. (2014). Sound Generating Flow Structures in a Thick Orifice Plate Jet. In: Progress in Turbulence V: Proceedings of the iTi Conference in Turbulence 2012. Paper presented at 5th iTi Conference in Turbulence, 2012; Bertinoro; Italy; 25 April 2012 through 25 April 2012 (pp. 201-204). Cham, Switzerland: Springer
Open this publication in new window or tab >>Sound Generating Flow Structures in a Thick Orifice Plate Jet
2014 (English)In: Progress in Turbulence V: Proceedings of the iTi Conference in Turbulence 2012, Cham, Switzerland: Springer, 2014, p. 201-204Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
Cham, Switzerland: Springer, 2014
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 149
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-161903 (URN)10.1007/978-3-319-01860-7_32 (DOI)2-s2.0-84943226056 (Scopus ID)978-3-319-01860-7 (ISBN)
External cooperation:
Conference
5th iTi Conference in Turbulence, 2012; Bertinoro; Italy; 25 April 2012 through 25 April 2012
Note

QC 20150330. QC 20160314

Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2016-09-01Bibliographically approved
O'Reilly, C. J., Alenius, E., Efraimsson, G. & Bodony, D. J. (2012). Aero-acoustic simulations of an orifice plate mounted in a low-Mach-number ducted flow. In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference): . Paper presented at 18th AIAA/CEAS Aeroacoustics Conference 2012 (33rd AIAA Aeroacoustics Conference); 4 June 2012 through 6 June 2012.
Open this publication in new window or tab >>Aero-acoustic simulations of an orifice plate mounted in a low-Mach-number ducted flow
2012 (English)In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Conference paper, Published paper (Other academic)
Abstract [en]

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

Keywords
A1. largeeddy simulations (LES), Aero-acoustic simulation, Dynamic mode decompositions, Finite difference operators, High-order finite differences, Orifice plate, Simultaneous approximation, Summation-by-parts
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-128991 (URN)10.2514/6.2012-2293 (DOI)2-s2.0-84880618566 (Scopus ID)978-160086932-7 (ISBN)
External cooperation:
Conference
18th AIAA/CEAS Aeroacoustics Conference 2012 (33rd AIAA Aeroacoustics Conference); 4 June 2012 through 6 June 2012
Note

QC 20130919

Available from: 2013-09-19 Created: 2013-09-17 Last updated: 2016-09-05Bibliographically approved
Alenius, E. (2012). Flow Duct Acoustics: An LES Approach. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Flow Duct Acoustics: An LES Approach
2012 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

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

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

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

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

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. p. viii, 175
Series
Trita-AVE, ISSN 1651-7660 ; 2012:70
Keywords
aero-acoustics, duct-acoustics, sound generation, acoustic scattering, acoustic-flow interaction, LES, IC-engines, orifice plate, confined jet
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-104777 (URN)978-91-7501-536-1 (ISBN)
Public defence
2012-11-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20121113

Available from: 2012-11-13 Created: 2012-11-12 Last updated: 2013-04-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4156-8976

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