###### Abstract  
When high-speed trains (HSTs) rapidly enter or exit the wind barrier area of the bridge, the quick change in the operating environment can lead to sudden changes in train aerodynamic loads, resulting in the deterioration of their aerodynamic performance and adversely affecting safe and stable operation. In this paper, the effects of wind barrier porosity, crosswind speed, and train speed on the sudden change in the aerodynamic load of the HST induced by wind barriers are analyzed, and the reasons for the sudden change from a flow field perspective are given. Additionally, the influences of the buffer structure with three lengths of 45 m, 90 m, and 135 m on the sudden change in the aerodynamic load of HSTs are studied. The results show that the lower the porosity of the wind barrier, the higher the crosswind speed, and the lower the speed of trains entering and exiting the wind barrier area, resulting in a greater degree of sudden change in the aerodynamic load of the HST. The buffer structure measuring 90 m in length is considered the most suitable, as it can significantly alleviate the sudden change in the aerodynamic load and effectively enhance the safety of train operations.  
crosswind; high-speed train; wind barrier; sudden change; buffer structure +
Footnote †: journal: Applied  
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their operating environment. The sudden transition in operating conditions leads to a sudden change in the aerodynamic load of the HST, thereby endangering its safe and steady operation.  
Some scholars have begun to focus on the impact of the sudden change in the aerodynamic load when passing through wind barriers on the dynamic performance of HSTs. [PERSON] et al. [12] conducted theoretical calculations to analyze the fluctuations in aerodynamic loads when HSTs traverse wind barriers on bridges. They developed a coupled dynamic model and examined the impact of the sudden change in the aerodynamic load on the safety index of a HST. [PERSON] et al. [13] conducted a comparative study to assess the aerodynamic characteristics of HSTs when passing through two different windproof facilities. Their findings indicated that during the moments of entering or exiting the windproof facility, there was a substantial increase in the fluctuation amplitude of the aerodynamic load of the HST, in contrast to other time intervals. [PERSON] et al. [14] conducted a study to examine the influence of sudden changes in the wind load induced by wind barriers on the dynamic response of HSTs using coupled numerical simulations. Their study revealed that wind barriers with lower porosity have a more substantial impact on the safety of HST operations. [PERSON] et al. [15] conducted a CFD analysis and found that when the HST traverses the windbreak transition between a cutting and an embankment under crosswind conditions, there is a notable increase in pressure, force, and moment coefficients, resulting in reduced safety of train operations. These studies primarily focus on the impact of the sudden change in the aerodynamic load on dynamic responses and running safety of HSTs. However, there is a lack of research on the factors affecting the degree of the sudden change in the aerodynamic load of the HST caused by wind barriers. Furthermore, specific or effective mitigation measures to address this issue have not been provided.  
This study utilizes the sliding mesh technique and the improved delayed detached-eddy simulation (IDDES) method to analyze the factors affecting the degree of the sudden change in the aerodynamic load when the HST passes through wind barrier areas in crosswind conditions and explains the reasons for the sudden change from the perspective of flow fields. Furthermore, three different lengths of buffer structures installed at the ends of the wind barriers are proposed, and their effectiveness in mitigating the sudden change is compared and analyzed.