Validation of a potential flow model for the prediction of the aerodynamic loads on track side objects

Abstract

Passing trains induce aerodynamic loads on track side objects or persons. For safety reasons, guide lines exist to protect persons standing near the track, e.g. track side workers or passengers waiting on platforms in railway stations. Since all new trains are first tested in model scale experiments, it is favourable to check the fulfillment of these guide lines in a sophisticated way. Currently, in industry, also computational fluid dynamics (CFD) are used to optimise train geometries according to their pressure pulse. However, these techniques are time-consuming, which is why there is a large interest on more efficient prediction tools. A priori it is unclear how the forces induced by the passing train can be scaled to full-scale trains and track side objects. Therefore the goal of this study is to achieve fundamental knowledge about the physical mechanism causing these forces and the impact of them on persons and objects on the one hand and to validate an efficient simulation tool on the other hand.The flow field around a train is characterised by three regions. The first one is associated with the pressure wave, generated by the nose of the train, the second one is induced by the boundary layer next to the train and the last region is the wake behind the train.Since the largest forces are caused by the nose pressure pulse, our main focus is on the nose region, which can be assumed as frictionless and incompressible. Thus, the induced pressure pulse can be reliable and efficiently predicted using potential flow theory. Experimental results, obtained in the ``Tunnel-Simulation-Facility'' in Göttingen (TSG), Germany, serve as background for qualifying the results of this theoretical model. In this facility, train models are accelerated by a hydraulic catapult and are moving free with full scale velocity through the test section. So far these TSG-measurements revealed that the aerodynamic loads on a generic track side object can be well predicted using potential flow theory.Another focus of the here presented studies is to investigate the scalability of the obtained forces. Thereby with the combination of the theoretical and experimental studies we want to clarify which contributions to the loads are the most important. The outcome will answer the question if commonly applied scaling of forces is justified or if more sophisticated laws are needed. The latter we also want to address at the conference.