The energy costs of rail freight cannot be denied anymore. Nowadays in Germany the energy costs mount up to about 22 % of the freight transportation costs, with a rising tendency. The design of freight wagons has hardly been paying attention to aerodynamics, although the speed has almost doubled since 1960 (65 km / h to 120 km / h empty). Particularly in the case of hopper wagons, which are known for having a very high traction resistance and for causing high traction power requirements when empty. As power needs, caused by the aerodynamic driving resistance, depend on the cube of speed, the obvious idea would be to slow down, in order to save costs. However, this is not feasible due to the fact that the infrastructure is more powerful, the more homogeneous all trains are operated. In mixed traffic of passengers and freight, even the slow trains should be as fast as possible, to cause as little drops in the line capacity. Empty freight wagons must now usually drive at 120 km/h, loaded ones at 100 km/h. Therefore, the main aim should be to make unloaded hopper wagons aerodynamically. This study focuses on the very modern hopper wagon, with pneumatic flap actuation, which is short and by its construction aerodynamically more favorable, than many other hopper wagons. Nevertheless, this wagon also still has considerable potential for more savings. When refitting an existing car with the here developed flow grids, the car will end up being a little heavier. A new car equipped with the flow grids is a little lighter, since the side walls are relieved by the flow grid. The strong vortex in the empty holds of the existing bulk wagon can be converted in many very small vortices which exist in the grating region only, by using the grating with a high base height. Thus air in the empty cargo holds remains at rest and the aerodynamic resistance is reduced so. The expenses for the aerodynamic grid may be cost neutral for new wagons because of possible reductions at other locations.


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