Train aerodynamics
Over the last years, Computational Fluid Dynamics (CFD) has evolved as a design tool for the railway vehicle industry.
During the last years I worked in close collaboration with Stadler Rail to better understand airflow around and in trains. For the GTW articulated railcar, the ventilation of the cooling system was deeply studied. The proper ventilation of air therein was of particular interest to ensure passengers safety. In 2012 the Swiss Federal Railways (SBB) issued a tender for 29 high-speed double-decker trains for international services between Germany, Switzerland and Italy via the Gotthard Base Tunnel, which is due to open in 2016. This high-speed train should be either 100 or 200 m long (respectively 4 and 8 carriages), which can be coupled together to a maximum total train length of 400 m (16 carriages). Together with NOSE Design AG many different nose shapes were carefully investigated to improve the overall aerodynamic efficiency of the complete train configuration.
The Creo Elements/Direct Modeling Express 4.0 software was used to create the STL file of the 3-cars generic train shown hereafter. Then the snappyHexMesh utility was used to generate the grid around the train. The explanation of the different steps involved in the snappyHexMesh process of mesh generation can be found here. Hovering over some thumbnails will enlarge the pictures.
A large range of side wind angles around the train in forward run have been computed. The following pictures show the pressure contours on train and ground for 3 different side wind angles. Streamlines have been overlaid.
Below, the left animation shows the variation of pressure on cars depending of the angle of attack of the wind. The grey arrow indicates the wind direction. The right video presents a cutting plane traveling from head car to end car. Pressure contours are plotted on surfaces. More animations regarding various kind of flow types are available here.
CFD can help engineers and designers to produce safer trains for passengers and railway workers. Many problems related to TSIs specifications can be investigated: analysis of the pantograph region, side wind effects, analysis of a train passing near a side wall and slip stream effect on a railway platform.
On the right hand side, two snapshots of more advanced simulations are presented, e.g. a train passing through a tunnel.
[1] Sanchi, Stéphane and Vos, Jan. Air flow around trains, 27 Jun. 2011.
