Characteristics of the air flow underneath high-speed trains running on the ballast track

Abstract

The air flow underneath high-speed trains have been measured at full-scale for three types of high-speed trains running on two types of ballasted tracks, and the characteristics of the flow have been investigated and comparatively analyzed related to the train and track types. 6 Kiel probe rakes vertically distributed in 40 mm interval from just above the track surface have been employed to measure the temporal histories of wind velocity during the passage of train. The results show that the flow under test trains reached fully-developed state before the end of the second vehicle and maintains until the start of the last vehicle, and average velocities over the fully-developed region show very good consistency for no more than 3 repeated samples. The vertical profile of average velocity over the fully-developed region has been suggested as a useful model to represent the characteristics of the flow underneath high-speed trains, and equivalent roughness of the test trains and tracks have been obtained by introducing the analytical solution of the turbulent Couette flow. The resulting values of equivalent roughness of Korean high-speed trains ranged from 50 mm to 150 mm, and that of the ballast track was 150 mm.