Experimental investigation of the slipstream development around a container freight train using a moving model facility

Increases in the volume of trade within the UK rail freight industry have led to proposed increases in freight train speeds. There is a concern that the unsteady slipstream created around a moving freight train could have implications on efficiency and the safety of passengers waiting on platforms or trackside workers. This paper describes a series of moving model-scale experiments conducted at the University of Birmingham's TRAIN rig facility. Experiments were undertaken to assess the slipstream development of a container freight train and draw conclusions on flow characteristics. In this paper the term 'freight train' refers to a series of flatbed wagons loaded with ISO standard shipping containers hauled by a Class 66 locomotive. In-depth analysis of slipstream velocity and static pressure ensemble average results at train side and above the roof identified a series of key flow regions. Results within the boundary layer region exhibit an influence from container loading configuration. Slipstream magnitudes are larger than typical high speed passenger train results, which it is suggested is related to the vehicle shape. The effect of train length and train speed was also considered. A detailed analysis of the nature of slipstream velocity components in specific flow regions is investigated, and conclusions drawn on characteristic patterns and factors influencing possible safety issues. The analysis highlighted differences created through decreased container loading efficiencies, creating increased boundary layer growth with a larger displacement thickness with higher turbulence intensities. Integral time and length scales calculated through autocorrelation indicate that proposed limits of human instability are exceeded for the container freight train with a lower loading efficiency. Overall the results from this paper offer for the first time a definitive experimental study on container freight slipstream characteristics, allowing the nature of the flow field around freight trains to be understood in far greater detail than before.