Particle image velocimetry of the underfloor flow for generic high-speed train models in a water towing tank

Abstract

The underfloor flow field 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 × 10⁶) over smooth ground, rough ground, and ground with sleepers is measured by means of two-component particle image velocimetry. The reference train model, consisting of four cars, features inter-car gaps and two bogies per car. These features are removed and all gaps are closed to create the smooth train configuration whereas the rough train configuration has all the gaps but no bogies. The lowest underfloor flow velocities and velocity gradients at the ground are observed for the smooth train model on the ground with sleepers. Furthermore, the measurements reveal that any additional irregularity of the underbody leads to regions characterised by flow acceleration in the otherwise Couette-like flow and this increases the possibility of ballast flight. Therefore, it is concluded that a smooth underbody can lower the risk of ballast flight. The results obtained for the reference train model are compared with those of a full-scale measurement. It is shown that the results of the water towing tank experiments with the scaled train model reflect the main characteristics of the underfloor flow of the full-scale measurements.