Unsteady onflow effects on model train drag

The DLR NGT-Cargo concept aims to increase the rail share of the European freight traffic market. Computational Fluid Dynamics (CFD) is a useful tool in analysing high-speed operations which are an important part of this concept. Standards provide guidelines for CFD assessments at cross-wind conditions using the RANS (Reynolds-averaged Navier-Stokes) equations. The development of aerodynamic forces under unsteady on-flows should be analysed within the context of these standards. A major challenge in satisfying these guidelines arises because of the multi-scale nature of these flows which are characterized by a large range of energetically significant flow scales. Wind-tunnel measurements, focussed on the development of the aerodynamic forces acting on a train, are being currently performed on a 1:25 scaled NGT model in the cross-wind facility Seitenwindversuchsanlage G¨ottingen (SWG) located at the DLR G¨ottingen. A CFD study is running concurrently. The aim of this study is to assess the ability of CFD approaches to reproduce both the observed on-flow conditions as well as the aerodynamic drag of the vehicle.