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Keywords: underfloor aerodynamics, ballast flight, ballast projection, high-speed trains, train aerodynamics, vehicle aerodynamics, particle image velocimetry.

Abstract

The underfloor flow field in the trackbed symmetry line was measured for three different 1:50 generic high-speed train configurations hauled through a water towing tank over a smooth ground, a rough ground, and a ground with sleepers at a speed of 4 m/s (Re = 0.25 Mio) by means of two-component high-speed particle image velocimetry. The measured high-speed train configurations were realised by altering the underfloor of a 4-unit generic high-speed train model. The reference train model represents a conventional high-speed train featuring two bogies per train car and inter-car gaps. The train configuration without bogies and all gaps left opened is referred to as the rough train model. The third configuration, denoted as the smooth train model, is characterized by a completely smooth underbelly, and obtained by removing all bogies and covering all gaps on the train underfloor.

Vertical and horizontal profiles of the mean velocity component in travelling direction U and vertical direction W and of their standard deviations reveal that all underfloor irregularities such as bogies, bogie housings, inter-car gaps, cavities and any other protruding obstacles increase the local and overall values of the velocities, velocity fluctuations and velocity gradients at the ground. Therefore, they lead to higher loads on the trackbed which increases the chance of ballast flight. Vice versa, it is concluded that a smooth underfloor lowers the risk of ballast flight. Additionally, the risk of ballast flight is higher for a trackbed without than with sleepers since the sleepers shield the ballast from the underfloor flow. Nevertheless, ballast lying on top of a sleeper is considered as the worst case scenario arising from the accelerated flow over the sleepers. The results were compared to full-scale measurements disclosing that the main characteristics of the underfloor flow are captured in the water towing tank for downscaled train models.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	International Journal of Railway Technology ISSN 2049-5358 IJRT, Volume 1, Issue 4, 2012 Underfloor Flow Measurements of 1:50 Generic High-Speed Train Configurations for Different Ground Conditions in a Water Towing Tank M. Jönsson, C. Wagner and S. Loose Department of Fluid Systems, Institute of Aerodynamics and Flow Technology, German Aerospace Center, Göttingen doi:10.4203/ijrt.1.4.5 purchase the full-text of this paper Full Bibliographic Reference for this paper M. Jönsson, C. Wagner, S. Loose, "Underfloor Flow Measurements of 1:50 Generic High-Speed Train Configurations for Different Ground Conditions in a Water Towing Tank", International Journal of Railway Technology, 1(4), 85-113, 2012. doi:10.4203/ijrt.1.4.5 Keywords: underfloor aerodynamics, ballast flight, ballast projection, high-speed trains, train aerodynamics, vehicle aerodynamics, particle image velocimetry. Abstract The underfloor flow field in the trackbed symmetry line was measured for three different 1:50 generic high-speed train configurations hauled through a water towing tank over a smooth ground, a rough ground, and a ground with sleepers at a speed of 4 m/s (Re = 0.25 Mio) by means of two-component high-speed particle image velocimetry. The measured high-speed train configurations were realised by altering the underfloor of a 4-unit generic high-speed train model. The reference train model represents a conventional high-speed train featuring two bogies per train car and inter-car gaps. The train configuration without bogies and all gaps left opened is referred to as the rough train model. The third configuration, denoted as the smooth train model, is characterized by a completely smooth underbelly, and obtained by removing all bogies and covering all gaps on the train underfloor. Vertical and horizontal profiles of the mean velocity component in travelling direction U and vertical direction W and of their standard deviations reveal that all underfloor irregularities such as bogies, bogie housings, inter-car gaps, cavities and any other protruding obstacles increase the local and overall values of the velocities, velocity fluctuations and velocity gradients at the ground. Therefore, they lead to higher loads on the trackbed which increases the chance of ballast flight. Vice versa, it is concluded that a smooth underfloor lowers the risk of ballast flight. Additionally, the risk of ballast flight is higher for a trackbed without than with sleepers since the sleepers shield the ballast from the underfloor flow. Nevertheless, ballast lying on top of a sleeper is considered as the worst case scenario arising from the accelerated flow over the sleepers. The results were compared to full-scale measurements disclosing that the main characteristics of the underfloor flow are captured in the water towing tank for downscaled train models. purchase the full-text of this paper (price £20) go to the previous paper return to the table of contents return to IJRT purchase this issue (price £70 +P&P)
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