Zijian Guo

Surface microstructures have shown potential for drag reduction, but their effectiveness on maglev trains remains unclear. This study numerically investigates a 1:20-scale TR08 maglev train with hemispherical dimples arranged on either the streamlined head (HeadConcave) or tail (TailConcave), using large-eddy simulation at 400 km/h to evaluate aerodynamic force, surface pressure behavior, and surrounding wake flow. Results show that TailConcave achieves the best overall performance, reducing the total drag coefficient to 0.1597, about 2.0% lower than the Prototype, mainly through a 2.7% reduction in pressure drag, while HeadConcave increases drag by about 1.5%. Surface-pressure analysis indicates that head dimples intensify local suction and recirculation, promoting earlier separation, whereas tail dimples lower the tail pressure coefficient, smooth pressure recovery, and weaken pressure fluctuations near the tail shoulder, symmetry plane, and guideway-side surface. Wake-flow analysis further shows that TailConcave delays tail separation, extends the dominant vortices downstream, and reduces Reynolds shear stress and turbulent kinetic energy in the near wake. Overall, rear-surface dimples provide a more effective drag-reduction strategy than front-surface dimples.

Under strong winds, the effect of sudden windbreak transition (WT) on high-speed trains is severe, leading to a deterioration of train aerodynamics and sudden yawing motion of the car body. To address these problems, based on a high-speed train and the specific geometric conditions derived from Xinjiang railway, first, the impact of a WT on the train and reasons for sudden changes in aerodynamic forces were determined by flow structural analysis. Furthermore, based on a multibody system dynamic model, the dynamic responses to WT were analysed. The results show that the impacts of WT were the strongest on the head car. WT had a strong effect on the train due to the unreasonable structural shape and the insufficient height of the windbreak in the transition region. This led to a strong push effect on the train; subsequently, the train’s dynamic characteristics deteriorated.

Due to the deterioration of the crosswind-protection performance of the original earth embankment windbreak walls on the train with increased speed, researching the influence of the heightened windbreak walls on aerodynamic performances of trains as well as the protection of the catenary is necessary for optimizing the windproof performance. The improved delayed detached eddy simulation based on the shear stress transport (SST) κ-ω turbulence model was employed to simulate flow structures. Furthermore, the effect on the displacement of the catenary was investigated using the finite element method (FEM). The numerical case was validated against the field tests. The results show that the aerodynamic performances of the train were improved as the windbreak wall was heightened by 0.5 m. Whereas, further heightening the windbreak wall worsened the aerodynamic performance. When the windbreak wall was heightened by 0.5 and 1 m, the wind speed of the catenary was reduced by 31.17% and 53.87%, and the displacement of the catenary was reduced by 48.09% and 74.11%, respectively, compared with that of the original windbreak wall. These results reveal that the wind-protection performance on the train and catenary can be both improved by reasonably heightening windbreak walls.

The improved delayed detached-eddy simulation (IDDES) method was used in this study to explore the influence of windbreak wall end shape on the wind tunnel test of the high-speed train aerodynamic characteristics. Affected by three different types of windbreak walls (long-enough, rounded-end, and blunt-end), the aerodynamic force, pressure distributions on the train surface, and flow fields around the train were compared and analyised mainly under a yaw angle of 30°. A wind tunnel test was carried out to verify the reliability of the numerical calculation method. Windbreak walls with different end shapes mainly exert an effect on the flow field in the region between the front end of the windbreak wall and the nose of the head car. However, the influence on the aerodynamic load and surface pressure distribution of the train is local, so the end of the windbreak wall can be blunt for convenience in the wind tunnel test. In addition, the length of the windbreak wall is an important factor affecting the accuracy of the wind tunnel test.

High-speed trains serving in a crosswind region are bearing more significant safety risks. Based on the three-dimensional (3D) Unsteady Reynolds-Averaged Navier–Stokes (URANS) turbulence model, a Computational Fluid Dynamics (CFD) computational work was conducted in the present study to predict the transient aerodynamic load of the train. The transient aerodynamic load was then employed as the input of the dynamic system to perform a dynamic analysis of running safety. Noticeable changes in the aerodynamic coefficients were found when the train entered and left the crosswind region due to the dramatic change in flow patterns. The original posture also provided significant changes to the train’s aerodynamic responses. A slightly larger maximum derailment coefficient was found on the first bogie of the leading car with a preset posture. There were obvious differences in the displacement characteristics of the three cars in the lateral direction and the rolling rotation, and the magnitude of the posture changes decreased from the leading car to the trailing car. The train with the consideration of posture was proven to withstand weaker crosswinds.

Railway track models with sloped subgrade ends, are commonly used in studies of train. In the present work, the effect of subgrade-end slope under a yaw angle of 30° was investigated by delayed detached eddy simulation (DDES) using one-eighth-scale train and single-track rail models. The obtained results were validated with wind tunnel tests. Time-averaged aerodynamic coefficients, pressure distribution, and flow field around the train were analysed and compared in three cases with different subgrade-end slopes. The results show that, the lift force of three cars is reduced with increasing subgrade-end slope, while the side force is found to be increased with increasing slope; the overturning moment of head and middle car decrease but which of tail increase. The extreme values occur in the case of 60°. Furthermore, the subgrade-end slope gives a variable impact on pressure distribution and flow pattern in different regions. This work has guiding significance for the selection of rail models in the subsequent train aerodynamic studies.

The CFD (Computational Fluid Dynamics) numerical simulation method with the DES (detached eddy simulation) approach was adopted in this paper to investigate and compare the aerodynamic performance, pressure distributions of the train surface, and flow fields near the train model placed above the subgrade with non-rail, realistic rail, and simplified rail models under crosswind. The numerical methods were verified with the wind tunnel tests. Significant differences in aerodynamic performances of the train body and bogie were found in the cases with and without a rail model as the presence of the rail model had significant impacts on the flow field underneath the vehicle. A larger yaw angle can result in a more significant difference in aerodynamic coefficients. The deviations of the train aerodynamic forces and the pressure distribution on the train body with the realistic and simplified rail models were not significant. It was concluded that a rail model is necessary to get more realistic results, especially for large yaw angle conditions. Moreover, a simplified rectangular rail model is suggested to be employed instead of the realistic rail and is capable to get accurate results.