In relation to aerodynamically induced ballast projection the main aspects have been explained. The character of the flow field and induced aerodynamic load has in some detail been shown for two very high speed trains. Some characteristics are similar: negative velocity under the front, repeating pattern associated with the period of the car passing and high peak just after the rear. However the distribution, which depends on the roughness of the lower part of the train and air exhaust flow towards the track, are very different as a result of the train consist and design. Locomotive driven trains have the highest airspeeds under the first and last cars, whereas EMU's have an acceleration of the flow over the first 2-3 cars. The flow under a train is very turbulent. To understand the flow ensemble averages need to be formed. Individual runs can have quite different flow, in particular related to a certain position under the train seen by a track fixed position. Many runs are required to have low uncertainty in the ensemble mean. The turbulent quantities have higher uncertainty than the mean. By additionally using spatial averaging of the ensemble quantities the uncertainty can be further reduced. A minimum of 20 runs or independent samples is a compromise between accuracy and effort. A slight speed dependence is present most likely associated with ventilation airflows, and can therefore vary between trains. However, a train tested at its maximum speed is sufficient to scale the effect to other train speeds. There is as expected a strong influence of the track properties on the measured quantity, highlighting the fact that comparable results can only be attained on ground conditions that are artificial and reproducible. An approach developed within the AeroTRAIN project in order to treat the issue on European or worldwide basis rather than separately in each country is outlined. From an interoperability perspective this will save significant effort in testing. The approach relies on measuring the train performance independently from the track properties on a standard ground configuration, allowing comparison of vehicles. The track performance is attained through tests or experience of the train together with the track. With a risk parameter or assessment quantity representative of the phenomena, train and track performances can be linked in a ballast performance chart. A limit can be defined and treatment of non-compliant trains or tracks addressed. Once the overall approach is validated and the track strength defined, in principle it will be sufficient to only test the train once on the standard ground configuration. The standard ground configuration proposed consists of smooth plates fitted in between the tracks. It has been shown that the relative performance of trains is the same as on the ballasted track.
Assessment of aerodynamic loads for structural requirements of railway vehicle bodies
2013
10 Seiten, 6 Bilder, 7 Tabellen, 9 Quellen
Conference paper
English
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