Cavity structure of aerodynamic braking devices and influence on high-speed train aerodynamic characteristics and vibration characteristics

As high-speed train speeds continue to rise, traditional friction braking fails to deliver efficient emergency braking—making aerodynamic braking devices (ABDs) a key solution for boosting high-speed train operational safety. However, the internal cavity structures of ABDs induce complex flow-induced vibrations and aerodynamic instabilities, which not only impair the train's aerodynamic performance but also threaten its operational safety. This study focuses on the length-depth ratio (L/D) of cavity structures in high-speed train ABDs, aiming to investigate how this key geometric parameter influences the flow field structure, aerodynamic characteristics, and vibration characteristics of ABDs. To address this research objective, the study adopts computational fluid dynamics based on the improved delayed detached eddy simulation model—this model is used to simulate the unsteady flow field structures of ABDs with different L/D, while unsteady aerodynamic characteristics of the devices are further analyzed in both time and frequency domains. Additionally, a vehicle system dynamics model is established to further analyze the effects of varying L/D on the train's vibration responses and ride comfort. The results show that L/D regulates the vortex shedding mechanism of ABDs: at L/D = 2.5, compact high-frequency vortices cause prominent drag fluctuations; cavity pressure pulsations have a moderate positive correlation with L/D, peaking at 7678.5 Pa when L/D = 10. Installing ABDs reduces the axle lateral force by 18.7%–22.1%, and L/D = 5 optimizes lateral performance while maintaining vertical stability. This work verifies ABDs' applicability and clarifies the aerodynamic-vibration coupling mechanism, providing a theoretical basis for aerodynamic braking system design.