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Wake characteristics of high-speed trains with different lengths
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-9061-4174
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-7864-3071
2014 (English)In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 4, 333-342 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2014. Vol. 228, no 4, 333-342 p.
Keyword [en]
Detached eddy simulation, aerodynamic train model, proper orthogonal decomposition, slipstream, train aerodynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-94099DOI: 10.1177/0954409712473922ISI: 000335657000001Scopus ID: 2-s2.0-84899802755OAI: oai:DiVA.org:kth-94099DiVA: diva2:525304
Projects
Gröna Tåget: Front shape and slipstream for wide body trains at higher speeds
Note

QC 20140625. Updated from submitted to published.

Available from: 2012-05-07 Created: 2012-05-07 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Slipstream and Flow Structures in the Near Wake of High-Speed Trains
Open this publication in new window or tab >>Slipstream and Flow Structures in the Near Wake of High-Speed Trains
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Train transportation is a vital part of the transportation system of today. Asthe speed of the trains increase, the aerodynamic effects become more impor-tant. One aerodynamic effect that is of vital importance for passengers’ andtrack workers’ safety is slipstream, i.e. the induced velocities by the train.Safety requirements for slipstream are regulated in the Technical Specificationsfor Interoperability (TSI). Earlier experimental studies have found that forhigh-speed passenger trains the largest slipstream velocities occur in the wake.Therefore, in order to study slipstream of high-speed trains, the work in thisthesis is devoted to wake flows. First a test case, a surface-mounted cube, issimulated to test the analysis methodology that is later applied to two differ-ent train geometries, the Aerodynamic Train Model (ATM) and the CRH1.The flow is simulated with Delayed-Detached Eddy Simulation (DDES) andthe computed flow field is decomposed into modes with Proper Orthogonal De-composition (POD) and Dynamic Mode Decomposition (DMD). The computedmodes on the surface-mounted cube compare well with prior studies, whichvalidates the use of DDES together with POD/DMD. To ensure that enoughsnapshots are used to compute the POD and DMD modes, a method to inves-tigate the convergence is proposed for each decomposition method. It is foundthat there is a separation bubble behind the CRH1 and two counter-rotatingvortices behind the ATM. Even though the two geometries have different flowtopologies, the dominant flow structure in the wake in terms of energy is thesame, namely vortex shedding. Vortex shedding is also found to be the mostimportant flow structure for slipstream, at the TSI position. In addition, threeconfigurations of the ATM with different number of cars are simulated, in orderto investigate the effect of the size of the boundary layer on the flow structures.The most dominant structure is the same for all configurations, however, theStrouhal number decreases as the momentum thickness increases. The velocityin ground fixed probes are extracted from the flow, in order to investigate theslipstream velocity defined by the TSI. A large scatter in peak position andvalue for the different probes are found. Investigating the mean velocity atdifferent distances from the train side wall, indicates that wider versions of thesame train will create larger slipstream velocities.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 64 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2012:28
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-94182 (URN)978-91-7501-392-3 (ISBN)
Public defence
2012-06-13, F3, Lindstedsv. 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20120530

Available from: 2012-05-30 Created: 2012-05-09 Last updated: 2014-02-11Bibliographically approved

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Efraimsson, GunillaHenningson, Dan S.

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