Aerodynamic and hydrodynamics aspects of the operation of trains through floodwater

Abstract eng:
This paper presents the results of an investigation into the physical mechanisms (hydrodynamic and aerodynamic) that are important when trains run through flood water. Undertaken on behalf of the Railway Safety and Standards Board (RSSB) the work comprised model-scale experiments, computational fluid dynamics (CFD) simulations and analytical modelling. The results of the modelling and analytical procedure showed that there was no discernible influence of the aerodynamics on the flood water that was below the rail head. However, when the wheel flanges came into contact with the water there was inevitably some splashing. The model-scale experiments and analytical model show reasonable agreement. INTRODUCTION In the operation of railways in the UK, rainfall (or other sources of water) can accumulate on the track and cause flooding. It is common practice for train operating companies (TOCs) to allow their rolling stock to run through flood water although this is usually at some reduced speed. Reduced train speeds lead to train delays which is has a negative influence on the economy and the perception of the rail industry as a whole. The recommendation from RSSB and individual TOCs on how fast trains should run through flooded rails significantly varies. For example, when flood water is above the sleepers but below the railhead RSSB and other TOCs train speeds recommend running speeds between 30 and 125 mph. The advice to drivers lacks consistency across the industry and does not appear to be informed by scientific reasoning. For this reason the University of Birmingham was commissioned by RSSB to develop a scientifically-backed set of rules for train speeds when operating through flood water of different depths relative to features on the rail, i.e. foot, rail head etc. The flood water that is not in contact with the wheel flanges (below rail head) is hypothesised to move as a result of the aerodynamic influence of the slipstream beneath the train, whereas in cases of water level above the bottom of the railhead, the movement of water was anticipated to be largely due to wheel flange/water interaction. The project used a combination of physical, numerical and analytical modelling to determine the influence of flood water height on the interaction with trains due to effects such as splashing. This paper contains an overview of the salient aspects of the three modelling techniques used to investigate this problem and then presents results from the one-dimensional analytical model.

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