The numerical simulation based on Reynolds time-averaged equation is one of the approved methods to evaluate the aerodynamic performance of trains in crosswind. However, there are several turbulence models, trains may present different aerodynamic performances in crosswind using different turbulence models. In order to select the most suitable turbulence model, the inter-city express 2 (ICE2) model is chosen as a research object, 6 different turbulence models are used to simulate the flow characteristics, surface pressure and aerodynamic forces of the train in crosswind, respectively. 6 turbulence models are the standard k-ε , Renormalization Group (RNG) k-ε , Realizable k-ε , Shear Stress Transport (SST) k-ω , standard k-ω and Spalart–Allmaras (SPA), respectively. The numerical results and the wind tunnel experimental data are compared. The results show that the most accurate model for predicting the surface pressure of the train is SST k-ω , followed by Realizable k-ε . Compared with the experimental result, the error of the side force coefficient obtained by SST k-ω and Realizable k-ε turbulence model is less than 1 %. The most accurate prediction for the lift force coefficient is achieved by SST k-ω , followed by RNG k-ε . By comparing 6 different turbulence models, the SST k-ω model is most suitable for the numerical simulation of the aerodynamic behavior of trains in crosswind.

Shear stress transport (SST) k–ω model and detached eddy simulation (DES) have been widely applied in crosswind stability simulations for trains in the literature. In the previous research, the influence of the SST and DES approaches on the flow field around trains, which affects the surface pressure and consequently the aerodynamic forces of the train, was not properly investigated in terms of their influence flow field. The SST and improved delayed detached eddy simulation (IDDES) turbulence models have been tested in this study for their ability to predict the flow field around, surface pressure, and aerodynamic forces on a 1/25th scale Class 390 train subjected to crosswinds. Numerical simulation results were validated with experimental data. Results show that both SST and IDDES predict similar trends in the mean flow field around the train. However, there were some slight differences observed in the size of vortices, the position of separation points, and consequently, the separation and attachment lines. The SST results compared more closely to the experimental data than IDDES for pressure coefficient on the leeward surface and roof at certain loops. Slight differences were observed in force coefficients for SST and DES. The side force coefficients calculated using computational fluid dynamics (CFD) sit within the experimental uncertainty, whereas the lift force coefficients deviated greatly due to the omission of some underbody geometrical features. Both SST and IDDES approaches used the linear-upwind stabilized transport (LUST) scheme and were able to predict accurately the time-averaged surface pressure within the margin of the experimental uncertainty.

A new vertical stiffness formula, including a term incorporating the rate of change of the effective area of a belted air spring, is established. Quasi-static vertical stiffness values are calculated using the formula. And four different experimental methods are used to study static and quasi-static vertical stiffness of a belted air spring. Results calculated using the formula are consistent with the experimental data. When the reservoir is small or the load is heavy, we can precisely predict the static and quasi-static extents of vertical stiffness. Differences between theoretical and experimental results are also analysed. We study the influence of geometric parameters on vertical stiffness of a belted air spring. When a reservoir is added to decrease vertical stiffness, we show how to avoid negative stiffness.

Vortex generator (VG) is one of the potential technical tools to reduce the aerodynamic resistance of high-speed trains. The passive control resistance reduction research of a high-speed train is carried out by using VG. Three typical installation locations, including flow separation point, boundary layer mutation and streamline transition location, and several nearby locations were selected to study the effect of VG location on the train aerodynamic characteristics. The results show that the tail car drag is significantly reduced when the VG is arranged at the boundary layer mutation, the tail car’s resistance can be reduced by 15.42%. The tail car reduces resistance by 3.87% when VG is set at the flow separation point. By analyzing the flow field structure, we found that the VG arranged in front of the separation point triggers the flow separation, which destroys the balance between the separation and longitudinal vortex. It effectively reduces the strength of the separation vortex, thereby reducing the tail car’s aerodynamic drag. The research provides a new thought for the aerodynamic resistance reduction of high-speed trains, and is of great significance to break the limitations of traditional aerodynamic drag reduction technology of trains.