a b s t r a c tIncreases 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.

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The concept of autonomous road vehicles has recently gained a great deal of technical respectability. Expected advantages over normal driver-controlled vehicles are through increased safety, reliability and fuel efficiency. This paper presents a novel experimental study enabling for the first time a full understanding of the aerodynamic flow development of a long vehicle platoon. Moving model experiments were carried out at the University of Birmingham Transient Aerodynamic Investigation (TRAIN) rig facility on a 1/20th scale eight lorry platoon with three constant vehicle spacings. Slipstream velocity and pressures, as well as simultaneous on-board vehicle surface pressure measurements were made. Results indicated a highly turbulent boundary layer development, with slipstream pulse peaks near the front of each lorry; similar to previous findings on flows around container freight trains. The drag coefficient of an isolated lorry was in agreement with previous studies. There are substantial reductions in aerodynamic drag for the non-leading platoon vehicles. Drag results plateaued towards a constant value within the platoon. Vehicle spacing affected drag values, with decreases of 57% observed for the closest spacing of half a vehicle length, demonstrating the aerodynamic benefits of platooning.

This research aims to characterise the aerodynamic flow around a container freight train and investigate how changing the container loading configuration affects the magnitude of aerodynamic forces measured on a container. Experiments were carried out using a 1/25th scale moving model freight train at the University of Birmingham's TRAIN rig facility. The model was designed to enable different container loading configurations and train lengths to be tested. A series of experiments to measure slipstream velocities and static pressure were undertaken to assess the influence of container loading configuration. Experiments to measure aerodynamic loads on a container were carried out using an on-board pressure monitoring system built into a specifically designed measuring container. A collation of full scale freight data from previous studies provided a tool to validate model scale data.Analysis of freight data found it was possible to present slipstream results as a series of flow regions. Clear differences in slipstream development and aerodynamic load coefficients were observed for differing container loading configurations. Velocity and pressure magnitudes measured in the nose region were larger than values observed previously. For container loading efficiencies higher than 50% boundary layer growth stabilises rapidly, however, for less than 50% continual boundary layer growth was observed until after 100m when stabilisation occurs. Velocities in the lateral and vertical directions have magnitudes larger than previously observed; increasing the overall magnitude by ∼10%. Comparison of model and full scale data showed good agreement, indicating Reynolds number independence. An analysis of TSI safety limits found results lie close to, but do not break, existing limits. Aerodynamic load coefficients were compared with previous studies and shown to be characteristic of typical values measured for a 30• yaw angle; however, differences between static wind tunnel and moving model results were discovered.

In recent years, the concept of autonomous road vehicles has gained a great deal of technical respectability, with expected fuel benefits arising from running vehicles closely in platoons. However, the aerodynamics of such vehicles travelling in close proximity is still not understood. This paper presents for the first time a detailed study of drag benefits and the flow structure around a platoon of high-sided lorries, through conducting Delayed Detached Eddy Simulations (DDES). The lorry surface pressure and slipstream flow characteristics show good agreement with experimental data. Drag reductions of up to 70% have been observed for all trailing lorries in the platoon. Analysis of the flow field indicated highly turbulent regions on the top and sides of trailing lorries. Turbulent kinetic energy and Reynolds stresses were found to concentrate at the connection region between lorry cab and box. Spectral analysis of the side forces identified oscillating behaviour on each lorry in the platoon due to strong vortex shedding, suggesting that platooning lorries are potentially more likely to develop lateral instabilities than an isolated lorry. The study indicates that autonomous vehicle developers and operators should consider the significant drag reduction benefits of platooning against the risk associated with potential lateral instabilities.