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Detached Eddy Simulation and Validation on the Aerodynamic Train Model
KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Aerodynamik.
Vise andre og tillknytning
2009 (engelsk)Inngår i: EUROMECH COLLOQUIUM 509: Vehicle Aerodynamics, 2009Konferansepaper, Publicerat paper (Annet vitenskapelig)
Abstract [en]

We present CFD-simulations of the flow around the aerodynamic train model(ATM). The turbulence modelling technique is detached eddy-simulation(DES), where the DES model is based on the k-ω SST RANS model. TheReynolds number for the simulation is 60.000 based on the hydraulic diame-ter (3m in full scale), free-stream velocity and kinematic viscosity of air. Themodel used is in 1:50 scale. The numerical results are compared to water tunnelexperimental data on the ATM available from the German Aerospace Center(DLR). The velocity field is measured using particle image velocimetry (PIV).The numerical setup is made to match the experimental setup as close as possi-ble. Focus of the analysis is on the flow in the wake of the train. Comparisonsof the averaged velocity and the velocity fluctuations in the wake shows that theoverall levels and trends are captured by the numerical simulations. However,the peak value of the velocity magnitude in the wake seems to be overestimatedby the DES technique used.

sted, utgiver, år, opplag, sider
2009.
Identifikatorer
URN: urn:nbn:se:kth:diva-12745OAI: oai:DiVA.org:kth-12745DiVA, id: diva2:318533
Prosjekter
Gröna Tåget
Merknad
QC 20100518Tilgjengelig fra: 2010-05-18 Laget: 2010-05-07 Sist oppdatert: 2012-03-21bibliografisk kontrollert
Inngår i avhandling
1. Analysis of Flow Structures in Wake Flows for Train Aerodynamics
Åpne denne publikasjonen i ny fane eller vindu >>Analysis of Flow Structures in Wake Flows for Train Aerodynamics
2010 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Train transportation is a vital part of the transportation system of today anddue to its safe and environmental friendly concept it will be even more impor-tant in the future. The speeds of trains have increased continuously and withhigher speeds the aerodynamic effects become even more important. One aero-dynamic effect that is of vital importance for passengers’ and track workers’safety is slipstream, i.e. the flow that is dragged by the train. Earlier ex-perimental studies have found that for high-speed passenger trains the largestslipstream velocities occur in the wake. Therefore the work in this thesis isdevoted to wake flows. First a test case, a surface-mounted cube, is simulatedto test the analysis methodology that is later applied to a train geometry, theAerodynamic Train Model (ATM). Results on both geometries are comparedwith other studies, which are either numerical or experimental. The comparisonfor the cube between simulated results and other studies is satisfactory, whiledue to a trip wire in the experiment the results for the ATM do not match.The computed flow fields are used to compute the POD and Koopman modes.For the cube this is done in two regions of the flow, one to compare with a priorpublished study Manhart & Wengle (1993) and another covering more of theflow and especially the wake of the cube. For the ATM, a region containing theimportant flow structures is identified in the wake, by looking at instantaneousand fluctuating velocities. To ensure converged POD modes two methods toinvestigate the convergence are proposed, tested and applied. Analysis of themodes enables the identification of the important flow structures. The flowtopologies of the two geometries are very different and the flow structures arealso different, but the same methodology can be applied in both cases. For thesurface-mounted cube, three groups of flow structures are found. First groupis the mean flow and then two kinds of perturbations around the mean flow.The first perturbation is at the edge of the wake, relating to the shear layerbetween the free stream and the disturbed flow. The second perturbation isinside the wake and is the convection of vortices. These groups would then betypical of the separation bubble that exists in the wake of the cube. For theATM the main flow topology consists of two counter rotating vortices. Thiscan be seen in the decomposed modes, which, except for the mean flow, almostonly contain flow structures relating to these vortices.

Publisher
s. 136
Serie
Trita-MEK, ISSN 0348-467X ; 2010:04
Emneord
Train Aerodynamics, Slipstream, Wake Flow, Detached-EddySimulation, Proper Orthogonal Decomposition, Koopman Mode Decomposi-tion, Surface-mounted Cube, Aerodynamic Train Model
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-12746 (URN)978-91-7415-651-5 (ISBN)
Presentation
2010-05-28, MWL74, Teknikringen 8, KTH, 13:15 (engelsk)
Opponent
Veileder
Prosjekter
Gröna Tåget
Merknad
QC 20100518Tilgjengelig fra: 2010-05-18 Laget: 2010-05-07 Sist oppdatert: 2012-03-21bibliografisk kontrollert

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