A review of freight train aerodynamics

Research on train aerodynamics has so far mostly focused on high-speed passenger trains. However, increasing evidence is being acquired showing that aerodynamic effects are also highly relevant to freight trains regarding their efficient and safe operation. Freight-train-specific aerodynamic phenomena become more relevant in light of the increase in freight train service speed expected to take place in the near future. For some decades now, experimental and numerical studies have been published about the aerodynamics of freight trains, and specifically of container trains. An overview of this effort is presented in this paper, the major points of agreement are summarized, and the open points in the field are identified. In the paper, the topology of the flow and the slipstream are described and their implications on the aerodynamic forces (both with and without crosswinds) are discussed. Special attention is given to aerodynamic resistance, drag and to the efforts made in literature to predict it using numerical and experimental methods. Furthermore, a comparison of the methods of investigation adopted in the field is presented, highlighting their suitability for the study of different problems. Finally, other topics like the risk for bystanders caused by slipstream effects, ballast flight and aerodynamics in tunnels are discussed. The literature review highlights the need to expand the research on freight train aerodynamics to freight train geometries different from intermodal container trains and to consider the many diverse geometries that may result from realistic mixed compositions of different wagon types.