Dynamic instability and discomfort of high-speed trains, in particular induced by aerodynamics in tunnels




PhD student: Lic. Eng. Ben Diedrichs
ben.diedrichs@se.transport.bombardier.com
Project leaders: Prof. Mats Berg
mabe@kth.se
Prof. Evert Andersson
everta@kth.se
Supervisors, fluid mechanics: Assist. Prof. Sinisa Krajnovic (main supervisor)
sinisa@chalmers.se

Prof. Lars Davidson (co-supervisor)
lada@chalmers.se
Partners: 1. KTH, Division of Aeronautical and Vehicle engineering, Department of Railway Technology
2. Chalmers, Department of Thermo and Fluid Dynamics.
3. Bombardier, Division of Intercity trains, Department of Specialist Engineering
Sponsors: Banverket (Swedish National Rail Administration) and partly by Bombardier Transportation in Sweden
Publications: [1,2]
Start of project: December 2002


Problem description and scope of study
The scope of the project is to explore the origin of lateral dynamic instability of high-speed trains related to aerodynamics and vehicle dynamics. These instability phenomena that induce vehicle oscillations can be strong enough to disrupt the passenger comfort and also to yield a more rapid mechanical wear of the rolling-stock and infrastructure. It is also a safety concern.

The problem is in much dependent on the factor of aerodynamic forcing over train weight, which has increased for modern trains, especially for non-motorized driving units and double deckers. As the traditional suspension systems are designed to reduce the influence of track irregularities by using soft enough springs and small enough dampers this obviously conflicts situations where forcing are applied directly to the body shell.

As far as the aerodynamics is concerned the applied forces and typical forcing frequencies scale with the flow speed squared and linearly, respectively. These basic facts brought together with the discrete natural eigenfrequencies of the vehicle, including the kinematic frequency due to wheel conicity, indicate that critical forcing can arise at some distinct train speeds. Therewith, the apprehension is that aerodynamic phenomena that are undiscovered or under control at lower speeds can quickly manifest themselves under these critical conditions depicted above.

One main object of the current project is aerodynamic simulations, see Figs. 1 and 2, and eventually measurements on real trains inside tunnels. The figures show surface pressures and wake flow velocity calculated with Large Eddy Simulations for a 25 m train inside a tunnel. The project will also explore the effects of vehicle motion on the aerodynamics and the interaction between vehicle dynamics and aerodynamics.


 
Fig. 1a. Pressure plotted on the surface of the body shell and tunnel walls.

 
Fig. 1b. Close up of Fig. 1a.

 
Fig. 2. Wake velocity plotted in a cross section 2m above the ground.
 

 
REFERENCES
  1. B. Diedrichs, M. Berg and S. Krajnovic, "Large Eddy Simulation of a typical European high-speed train inside tunnels", SAE 2004 World Congress, SAE Paper 2004-01-0229, Detroit, Michigan, USA, 2004
    View PDF file
     
  2. B. Diedrichs, M. Berg and S. Krajnovic, "Large Eddy Simulation of the Flow Around High-Speed Trains Cruising Inside Tunnels", ECCOMAS 2004, P. Neittaanmaki, T. Rossi, S. Korotov, E. Onate, J. Periaux, and D. Knorzer (eds.), July 24-28, Finland.
    View PDF file
     


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