Assessment of aerodynamic safety aspects with moving-model experiments

Abstract

Scale-model experiments are used to investigate train geometry concepts in efficient and more cost-effective conditions compared to full-scale tests. The assessment of aerodynamic safety aspects such as the maximum train-induced flow velocity - also referred to as slipstream - is of high interest in order to predict the success of approval tests. The tunnel simulation facility Göttingen is a moving-model rig used for experimental investigations of the flow around and behind scale train models. The present study focuses on the investigation of the large-scale flow structure in the wake of a generic train model using High-Speed Particle Image Velocimetry with cameras on both sides of the track. As previous studies have shown, the unsteady wake flow consists of highly turbulent, differently scaled structures, which lead to large variations between single runs. Therefore, 30 test runs are performed to provide statistically representative results. Conditional sampling is used to study the critical values with regard to the standards of the European Union as well as the instantaneous flow structure of the wake, which corresponds to the occurrence of the maximum velocity during a single run. The use of the moving average filter required by the EU standards has a major effect on the small-scale high-velocity flow structures in the wake. The large wake flow structure, which can be related with the average occurrence of the maximum flow velocity per run, remains present even with the long filter time. The oscillating wake flow can be observed in the measured flow field of the single runs as well as in the calculation of the lateral wake position relative to the track center.