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Research Papers: Flows in Complex Systems

# LES of the Slipstream of a Rotating Train

[+] Author and Article Information
Hassan Hemida1

School of Civil Engineering, University of Birmingham, B15 2TT, UKh.hemida@bham.ac.uk

Nahia Gil

School of Electrical Engineering, University of Birmingham, B15 2TT, UK

Chris Baker

School of Civil Engineering, University of Birmingham, B15 2TT, UK

1

Corresponding author.

J. Fluids Eng 132(5), 051103 (May 06, 2010) (9 pages) doi:10.1115/1.4001447 History: Received June 26, 2009; Revised March 05, 2010; Published May 06, 2010; Online May 06, 2010

## Abstract

The slipstream of a high-speed train was investigated using large-eddy simulation (LES). The subgrid stresses were modeled using the standard Smagorinsky model. The train model consisted of a four-coach of a 1/25 scale of the ICE2 train. The model was attached to a 3.61 m diameter rotating rig. The LES was made at two Reynolds numbers of 77,000 and 94,000 based on the height of the train and its speed. Three different computational meshes were used in the simulations: course, medium and fine. The coarse, medium, and fine meshes consisted of $6×106$, $10×106$, and $15×106$ nodes, respectively. The results of the fine mesh are in fairly agreement with the experimental data. Different flow regions were obtained using the LES: upstream region, nose region, boundary layer region, intercarriage gap region, tail region, and wake region. Localized velocity peak was obtained near the nose of the train. The maximum and minimum pressure values are also noticed near to the nose tip. Coherent structures were born at the nose and roof of the train. These structures were swept by the radial component of the velocity toward the outer side of the train. These structures extended for a long distance behind the train in the far wake flow. The intercarriage gaps and the underbody complexities, in the form of supporting cylinders, were shown to have large influences on the slipstream velocity. The results showed that the slipstream velocity is linearly proportional to the speed of the train in the range of our moderate Reynolds numbers.

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## Figures

Figure 1

Experimental set-up. (a) Train model and measuring probe. (b) Schematic diagram of the rail and train support.

Figure 2

Computational domain showing (a) dimensions of the rotating and stationary domains and (b) computational model and supporting cylinders

Figure 3

Medium mesh. (a) Surface mesh on and close to the intercarriage gap. (b) Cross section showing the mesh shape on and around the intercarriage gap. (c) Mesh around the nose of the train.

Figure 4

Schematic representation of the positions at which the slipstream velocities are measured

Figure 5

Slipstream velocity (based on the velocity magnitude) at half train height and a distance 0.084H from the outer surface (Re=77,000)

Figure 6

Slipstream velocity (based on the tangential velocity Vθ) at half train height and a distance 0.084H from the inner and outer surfaces (Re=77,000)

Figure 7

Slipstream at height 0.4H from the platform and 0.25H from the surface of the train (Muld (13)—used with permission): (a) based on the axial component of the velocity and (b) based on the velocity magnitude

Figure 8

Slipstream velocity (based on the tangential velocity Vθ) at 0.05H above the train at its centerline (Re=77,000)

Figure 9

Slipstream velocity (based on the velocity magnitude Vm) at half height of the body and a distance 0.14H from the outer surface (Re=77,000)

Figure 10

Slipstream velocity (based on the velocity magnitude Vm) at a distance 0.14H from the outer surface (Re=77,000)

Figure 11

Turbulent intensity at a distance 0.14H from the outer surface (Re=77,000)

Figure 12

Normalized displacement thickness above the train at its centerline (Re=77,000)

Figure 13

Normalized displacement thickness at half height of the train on the outer side (Re=77,000)

Figure 14

Plane at the half height of the train colored by the relative tangential velocity, showing the boundary layer thickness (Re=77,000)

Figure 15

Second invariant f the velocity gradient Q=2000 colored by the tangential velocity component Vθ(Re=77,000)

Figure 16

Plane at the half height of the train colored by time-averaged static pressure (Re=77,000)

Figure 17

Surface pressure coefficient on top and bottom faces of the train at its centerline (Re=77,000)

Figure 18

Surface pressure coefficient at one intercarriage gap length upstream and downstream of the second intercarriage gap (Re=77,000)

Figure 19

Pressure coefficient at distance 0.1H from the outer surface of the train (Re=77,000)

Figure 20

Slipstream velocity (based on the velocity magnitude) at half train height and a distance 0.05H from the outer surface

Figure 21

Turbulent intensity at half the train height and a distance 0.05H from the outer surface

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