Comparative analysis of windbreak configurations for unloaded gondola train cars under crosswinds based on computational fluid dynamics and multi-body dynamics

Understanding the aerodynamic and dynamic characteristics of unloaded freight trains in crosswinds is pivotal for ensuring their operational safety and reliability. The dynamic performance of unloaded gondola cars under varying windbreak heights is therefore investigated in this study, revealing distinct differences in lateral stability and safety indicators, and enabling the determination of an optimal windbreak height. A 3D unsteady aerodynamic model was developed using the improved delayed detached eddy simulation (IDDES) method and an overset numerical mesh. Also leveraging a multi-body dynamics (MBD) model of a three-wagon freight car configuration, we investigate time-averaged aerodynamic forces, transient flow field distributions, and nonlinear dynamic responses. Parametric analyses reveal a non-monotonic relationship between the height of the windbreak and the stability of the train. A windbreak with a critical height of 2 m (0.74 relative to the car body height) results in 76%, 64%, and 81% lower values of the derailment coefficient CD, wheel unloading ratio R, and overturning coefficient CO, respectively. Notably, when the height of the windbreak exceeds 2 m, vortices within the gondola induce an adverse pressure coefficient distribution (Cp=−2.17) on the leeward internal wall, intensifying the lateral force and overturning moment. Furthermore, frequency-domain analysis reveals that the lateral sway and overturning vibration mode are associated with low-frequency (1.61 Hz) lateral vibrations under crosswind conditions. This study provides a theoretical foundation for the design and optimization of railway windbreaks.