Experimental investigation of the flow field underneath a generic high-speed train and the effects of ground and train roughness

Abstract

Results obtained from two component Particle Image Velocimetry (PIV) measurements on three different 1:50 generic high-speed train configurations hauled through a water towing tank over a smooth (Plexiglas) and a rough (grinding belt) ground at a speed of 4 m/s are presented. Principally, the three different generic high-speed train configurations are based on the same model (front car, two cars and tail car). The smooth generic high-speed train configuration (smooth GHSTC) reflects no bogies and covers the bogie cut outs and inter car gaps, the rough generic high-speed train configuration (rough GHSTC) is obtained by removing the bogies and leave the bogie cut outs and inter car gaps open and for the generic high-speed train configuration (GHSTC) the bogies are not removed but the inter car gaps are left open. A PIV set-up was chosen that the light sheet defines a vertical plane (XZ) between the ground and the train in the symmetry line of the train. Comparing the PIV results obtained for the GHSTC with full scale measurements, it was found that the same flow structures develop in the vicinity of the head and the tail of the train. But, the measured underfloor U-velocity of the downscaled model measurements did not reach the same value as those measured for the full scale highspeed train. The reason which is ascribed to the better aerodynamic underframe of the train model in the downscaled model measurements. The flow field underneath the GHSTC was fully developed at the beginning of the second car, in agreement to the full scale measurements. For the three train configurations three different flow fields underneath the train were obtained. The lowest velocities were found for the smooth GHSTC and the highest for the rough GHSTC. Further, the ground roughness changed the flow fields underneath the different train configurations.