The flow around trains in the open air

Abstract This chapter gives an introduction to the flow around trains in the open air and provides the basic description of the flow field on which the discussion of the applications in Part 2 is based. The discussion is built on the results of full-scale experiments, for a wide range of different train types, with data from model-scale experiments and computational fluid dynamics being used where no full-scale data are available. Firstly, the flow around trains on level ground is discussed, and the five basic flow regions are introduced – the nose region, the boundary layer region, the near wake region, the far wake region and the underbody flow region. Each of these regions is then analysed in turn, and data for typical pressure and velocity fields are presented. Information is presented on nose peak-to-peak pressure coefficients: train side, roof and underbody boundary layer parameters and roof and underbody skin friction for different train types. The unsteady vortex flow in the near wake region of high-speed trains is discussed in qualitative terms. The discussion then moves on to consider the flow around trains on level ground in crosswinds, considering both low and high wind speed conditions. The complexity and transient nature of these flow fields is emphasised. Finally, the flow around trains in a range of different environments is presented, and the effects of ballast platform height, embankments, viaducts and different station environments are discussed.