The hexahedral dominated cell meshi

The hexahedral dominated cell meshing techniqueis employed to discretize the computational domain. Afiner resolution is required closed to the surface of trainand bridge in order to correctly reproduce the geometrical details and to better capture the flow features, andthe minimum cell size is set to 5 mm on the train surface,as shown in Figure 4. While a coarser cell is adopted farfrom the train and bridge zone where the flow is less perturbed and the turbulence effect is less important (Cheli,Ripamonti, Rocchi, & Tomasini, 2010). Some researches(Baker, 2010; Sterling, Baker, Jordan, & Johnson, 2008)reveal that the flow around train can be affected by thethickness of boundary layer and the corresponding y+value is 30–120 in order to meet the requirement of thestandard wall function used in the case. The finest boundary mesh in the surface of train and bridge is created to1 mm, and the total cells number is about 20 million inthe model.