High-Speed Train Aerodynamics

Large aerodynamic loads can be generated when two trains pass one another. The magnitude and duration of the load depends on the velocity and geometry of the two trains and also on the ambient wind speed and direction. From experience, we know that the largest changes in load are generated near the ends of the passing trains and that these loads can have serious consequences. In a study for the US Department of Transportation, we calculated the unsteady dynamic loads created when a high speed passenger train traveling at speeds up to 150 mph (241 km/hr) passes a slower freight carrying shipping containers and traveling at speeds up to 50 mph (80 km/hr) using the Acusolve finite element software. A series of calculations were used to explore the effects of train geometry and speed as well as the effects of ambient wind speed and direction.

Figure 1 shows pressure contours on the surface of the two trains and isobars on the ground at four times as the locomotive of the passenger train passes a single shipping container on a string of flat cars in the freight train. Visualizations such as this show that the strong pressure bubble ahead of the locomotive (red contours) and the low pressure area on the side of the cab (blue contours) create a push-pull effect on the container car.

The force resultants on the individual cars of the two trains were calculated by integrating the surface pressures at each time step. An example of the force resultant histories is shown in Figure 2. In this figure, Fx is the drag force on the container car, Fy is the lateral force and Fz is the vertical force. The positive X-axis is in the direction of the the passenger train and the Y-axis is directed away from the passenger train. The large excursions in Fy are the side-to-side loads on the container car. The dashed lines in the figure pinpoint the times at which the passenger locomotive reaches the front and back ends of the container car.

The large scale dynamic CFD calculations illustrated in the passing train problem can be applied to related problems including the passing of highway vehicles, the dynamic pressures generated by fan blades, and vortex shedding in marine and other environments.

References:

• MacNeill, R.A., Holmes, S., and Lee H.S., "Measurement of the Aerodynamic Pressures Produced by Passing Trains," Proceedings of: JRC2002, The 2002 ASME/IEEE Joint Rail Conference, Washington D.C., April 23-25, 2002.
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For inquiries or comments, please contact:
Robert MacNeill
Principal Engineer
e-mail: rmacneill@ara.com