The effect of the ground condition on high-speed train slipstream

Understanding the induced movement of air as a high-speed train passes (slipstream) is important for commuter and track-side worker safety. Slipstream is affected by the movement of the train relative to the ground, but this is difficult to include in wind-tunnel tests. Using simulations based on the Improved Delayed Detached Eddy Simulation model, this study investigates the effect of relative ground motion on slipstream for three different ground/wheel configurations: a stationary ground with stationary wheels, a moving ground with stationary wheels, and a moving ground with rotating wheels. By examining the interaction between the train-induced flow structure and ground boundary layer, this study identifies two ways that the ground boundary layer changes slipstream: through directly altering the high slipstream velocity region due to the ground boundary-layer development, and through indirect widening of the wake by deformation of the trailing vortices. The altered aerodynamic loading on a train due to relative ground motion is visualised through the surface pressure distribution, allowing the resultant impact on drag and lift to be assessed. For wheel rotation, it is concluded that its effect is mainly restricted to be within the bogie regions, with limited influence on the wake behind the train.