## 1 Introduction  
In strong wind areas, crosswinds are a typical safety risk for train operation, and train aerodynamics are important to consider [1, 2, 3]. High-speed trains are affected by various factors, including the nose and head shape, the car body shape, the pantograph, and the train speed [4]. Furthermore, wind speed is a key factor that been studied using prescribed yaw angles for various train speeds [5]. Various methods are applied to study train aerodynamics under crosswinds. Generally, full-scale tests can directly reflect the aerodynamic performance of a train [6, 7]. In the United Kingdom, [PERSON] et al. [8] compared the aerodynamic performances of trains using the CFD method, model testing, and full-scale tests under crosswinds. Due to the limitations of full-scale tests, such as the high cost and experimental settings, model tests are typically conducted, which include the wind tunnel and moving model tests [9, 10]. Various wind tunnel tests have been conducted with crosswinds, including studies of current and new train designs [11], investigation of the geometric details on train aerodynamics [12], etc. Pressure is easily measured with moving model tests, but aerodynamic forces are not easy to measure directly. Therefore, [PERSON] et al. [13] and [PERSON] et al. [14] developed a method for examination of the aerodynamic force characteristics of moving vehicles under crosswinds. With a focus on train stability under crosswinds, [PERSON] et al. [15] compared static and moving experimental resultsfor a model passenger train and found that there were small differences in the pressure distributions that were limited to the nose and underbody of the train. With advancements in computational efficiency, an increasing number of studies on train aerodynamics have been conducted using the CFD method [16], including studies on the effect of bogie's geometric complexity on force measurement, the slipstream of freight trains and passenger trains under crosswinds [17; 18], and the prediction performance of different turbulence models for train aerodynamics under crosswinds. Terrain and facilities surrounding the railway, including cuttings, embankments, bridges, and tunnels, affect trains in the presence of crosswinds [19; 20]. Owing to varying terrain, transition regions can be generated beside the railway. Under a crosswind, these transitions lead to an unsteady wind. Using a wind tunnel test, [PERSON] et al. [21] built a 1:20 scale model in an attempt to study train aerodynamics in the transition region between the subgrade and tunnel under crosswinds. The results of their study demonstrated that the impact of the transition from the cutting to the tunnel was greater than that of the embankment-tunnel transition. The effects of long-span bridge towers on a train were investigated by [PERSON] et al. [22] and [PERSON] et al. [23] using wind tunnel tests. The results demonstrated that due to the shielding effects of towers, sudden wind load changes considerably affect train aerodynamics. In addition, the findings indicated that the corresponding dynamic responses of the train fluctuated considerably. Windbreak walls are built to protect the running safety of trains under crosswinds due to their low cost and their effectiveness [24; 25]. Uniform and regular windbreaks result in a significant improvement in train safety in general; however, when the windbreak is built on varying terrain, windbreak transitions (WTs) occur along the railway. Sudden and irregular WTs affect a train's aerodynamic and dynamic performances [26]. For instance, a windbreak wall was built along the LanXin high-speed railway in China [27; 28]; however, some portions of this railway pass through complex landforms, which include flat ground, embankments, and cuttings.