URANS simulation of the slip stream of a high speed train

The recent development of high speed trains over the last decade led to a growing interest in their aerodynamics. Beside the aerodynamic loading on the train itself, some issues related to the train-infrastructure interaction have to be carefully taken into account. A train at full operational speed generates a strong induced airflow that may interact with the infrastructures near the trackside and may damage them, and they may also endanger the workers near the rails. In order to ensure the safety of both train passengers and trackside workers specific requirements imposed by the European regulations have to be fulfilled. Nowadays the tests required for the train homologation are based on full scale measurements of the airspeed in specified positions along the railway line. These ones are very expensive to be performed, they suffer from repeatability errors and they are time consuming. The purpose of this research is to focus on the slipstream issue and to analyse the problem both using the experimental approach required by the European standards and numerical CFD simulations. An important part of the work was initially dedicated to the post processing of an extensive experimental campaign performed on the Italian high speed line, in order to obtain reliable results to be used as for comparison with CFD results. Since the flow is highly turbulent, a statistical approach has to be adopted. CFD simulations have been performed on the full scale train geometry using both RANS and URANS approaches with a wall treatment based on the wall functions. Different setups have been compared in the CFD analysis, checking both mesh and turbulence models dependencies. These simulations highlighted the great complexity of the problem with an experimental measurement performed close to the shear layer of the train boundary layer. Encouraging results are obtained from the numerical analysis indicating the ability of the URANS with the SST turbulence model in the prediction of both the train induced flow and the turbulent structures around it.