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We present CFD-simulations of the flow around the aerodynamic train model(ATM). The turbulence modelling technique is detached eddy-simulation(DES), where the DES model is based on the k-ω SST RANS model. TheReynolds number for the simulation is 60.000 based on the hydraulic diame-ter (3m in full scale), free-stream velocity and kinematic viscosity of air. Themodel used is in 1:50 scale. The numerical results are compared to water tunnelexperimental data on the ATM available from the German Aerospace Center(DLR). The velocity field is measured using particle image velocimetry (PIV).The numerical setup is made to match the experimental setup as close as possi-ble. Focus of the analysis is on the flow in the wake of the train. Comparisonsof the averaged velocity and the velocity fluctuations in the wake shows that theoverall levels and trends are captured by the numerical simulations. However,the peak value of the velocity magnitude in the wake seems to be overestimatedby the DES technique used., QC 20100518, Gröna Tåget

Large-eddy simulations (LES) of a planar, asymmetric diffuser flow have been performed. The diverging angle of the inclined wall of the diffuser is chosen as 8.5 degrees, a case for which recent experimental data are available. Reasonable agreement between the LES and the experiments is obtained. The numerical method is further validated for diffuser flow with the diffuser wall inclined at a diverging angle of 10 degrees, which has served as a test case for a number of experimental as well as numerical studies in the literature (LES, RANS). For the present results, the subgrid-scale stresses have been closed using the dynamic Smagorinsky model. A resolution study has been performed, highlighting the disparity of the relevant temporal and spatial scales and thus the sensitivity of the simulation results to the specific numerical grids used. The effect of different Reynolds numbers of the inflowing, fully turbulent channel flow has been studied, in particular, Re-b = 4,500, Re-b = 9,000 and Re-b = 20,000 with Re-b being the Reynolds number based on the bulk velocity and channel half width. The results consistently show that by increasing the Reynolds number a clear trend towards a larger separated region is evident; at least for the studied, comparably low Reynolds-number regime. It is further shown that the small separated region occurring at the diffuser throat shows the opposite behaviour as the main separation region, i.e. the flow is separating less with higher Re-b . Moreover, the influence of the Reynolds number on the internal layer occurring at the non-inclined wall described in a recent study has also been assessed. It can be concluded that this region close to the upper, straight wall, is more distinct for larger Re-b . Additionally, the influence of temporal correlations arising from the commonly used periodic turbulent channel flow as inflow condition (similar to a precursor simulation) for the diffuser is assessed., QC 20100525