Particle Image Velocimetry of the underbody flow of generic high-speed trains

Abstract

Two component Particle Image Velocimetry (PIV) of the underbody flow of three different 1:50 generic high-speed train configurations hauled through a water towing tank over a smooth and a rough ground at a speed of 4 m/s (Re = 0.24 Mio) have been performed. The reference train model (RTM) consisting of 4 cars, features bogies and inter car gaps. All this features are removed for the clean train configuration (CTM), while the open train configuration (OTM) reflects all gaps but no bogies. The lowest underbody flow velocities were obtained for the CTM on the rough ground. It was found that any additional irregularity of the underfloor leads to accelerated flow regions which increase the possibility of ballast projection. The highest velocity gradients and thus aerodynamic loads on the ballast stones were obtained in the nearly fully-developed Couette-like flow underneath the third car of the RTM. Therefore it is concluded that a smooth underbody can lower the risk of ballast projection