Numerical Investigation of Sweeping-Jet Control at the Nose Region of a High-Speed Train

With the increase in operating speed, aerodynamic drag becomes a major part of the total resistance of high-speed trains. Further drag reduction by only optimizing the streamlined shape is difficult. In this study, a three-car high-speed train model was used to explore active drag reduction by sweeping jets. The improved delayed detached-eddy simulation (IDDES) method based on the SST k-ω turbulence model was adopted. An equivalent sweeping-jet model was used to reduce the computational cost. Three important parameters were considered: the outlet width of the sweeping-jet model, the jet angle, and the jet velocity. The results show that a larger jet outlet gives a stronger drag-reduction effect. When the ratio between the jet outlet width and the train width is 5:50, the total drag reduction in the three-car train reaches about 1.5%. When the jet angle is 120°, the total drag reduction reaches about 2.84%, and the middle car has the largest drag reduction of 6.19%. When the jet velocity is 0.30 times the incoming flow velocity, the total drag reduction reaches about 4.0%. The main flow-control mechanism is that the sweeping jet forms a low-speed recirculation region near the train surface. This region lifts the incoming flow, weakens its direct impact on the train body, and reduces the surface pressure in the controlled region. The results provide a useful basis for applying sweeping jets to aerodynamic drag reduction in high-speed trains.