Slipstream, which is caused by the movement of high-speed trains (HSTs) and transported mainly by the outward movement with the downstream development of the pair counter-rotating vortex, has been a threat to the railway facilities and staff near the line. Although the cause and distribution of slipstreams have been widely studied, the mechanism behind slipstreams needs to be further clarified. The detailed turbulence kinetic energy (TKE) budget analysis including the advection term, production term, and turbulence transport term in the wake region of the train is conducted to reveal the formation and distribution of the slipstream. Considering the fact that the HSTs can operate in the open air and inside the tunnel, this paper compares and analyzes the effect of the blocking ratio induced by the tunnel wall on the TKE budget, as well as the aerodynamic force, slipstream, and flow structure around trains. The findings demonstrate that the tunnel wall's blocking effect does not modify the vortex-shedding process or the flow pattern around the train. However, the time-averaged (U¯slipstream) and standard deviation (σslipstream) of the slipstream in the near wake are increased because of the tunnel wall blocking effect. Meanwhile, the displacement boundary layer and the momentum boundary layer are hindered by the tunnel wall-blocking effect. The analysis of the TKE budget in the wake of HSTs shows that the total advection is primarily driven by the streamwise velocity (Axk). When the distribution Axk intersects with the measuring position on both sides of the track, the maximum value U¯slipstream and its corresponding position are determined. The turbulence transport term Tu,yk dominates the total transport of TKE and the distribution of σslipstream. The Tu,yk transfers energy from the pair of counter-rotating vortex inward into the wake region and outward away from the vortex core when the turbulent wake interacts with the undisturbed mean flow.
