The underfloor flows of three different 1:50 generic high-speed train models hauled through a water towing tank at a speed of 4 m/s (Reynolds number = 0.24 Mio) over a smooth, a rough and a ground with sleepers were measured with two component high-speed PIV. The obtained horizontal profiles of the mean velocity component in travelling reveal that the underfloor flow can be divided into four characteristic regions. These are the head region, the Couette-like underfloor flow region, the near wake region and the far wake region. In the head region the flow is strongly accelerated followed by deceleration before developing to a Couette-like flow. The development to more or less fully developed Couette-like flow was found to be dependent on the train's underbody roughness. For the rough train model the flow was more or less fully developed below the second half of the train whereas for the smooth and the reference train model the Couette-like flow developed along the entire train length. In the near wake region the highest velocities are reached after a strong acceleration that decays in the far wake region. Comparing the results of the three considered train models showed that bogies, bogie cavities, inter-car gaps or any other protruding objects increase the local and overall velocities and the turbulence level in the underfloor flow and consequently increasing the risk of ballast flight. The rough ground and the sleepers have a positive effect regarding the risk of ballast flight since they slow down the flow and thus reduces the chance for ballast flight. The lowest U-velocities values were found for the smooth train model on the rough ground. Finally a comparison with full scale measurements with the Italian high-speed train ETR 500 disclosed that the main flow characteristics around the head, the underfloor flow and the tail are captured in the water towing tank experiments. The reasons for the differences are the different train geometries, the lower degree of geometrical detail of the train models underbody and the different Reynolds number.
High-speed particle image velocimetry of the underfloor flow of a generic high-speed train model
2012
15 Seiten, 12 Bilder, 17 Quellen
Conference paper
Storage medium
English
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