## 4 Results  
### Time-Varying Aerodynamic Coefficients  
Figure 7 shows the time history of the aerodynamic coefficients of each car during the train's passing from 100 m before the crosswind region to 100 m after the tail car exits. The speed of the train and the crosswind was 83.33 m/s and 20 m/s, respectively. In each figure, the times when the vehicle of interest entered and left the crosswind region were marked to correspond to the change in its aerodynamic coefficients. The results under different wind-protection conditions are included in each figure to compare the protective capacity of the wind barrier and the transient changes of the aerodynamic performance of the train passing through the wind barrier. Each coefficient is given a unified vertical axis range to compare the performance of different cars. The peak-to-peak value of the aerodynamic coefficients obtained when each car of the train entered and left the crosswind area was calculated and shown in Table 1, which numerically assisted the interpretation of fluctuations. Here, the period of \"entering\" and \"exiting\" was captured from 0.1 s before the corresponding car started to enter the crosswind region to 0.1 s after it ultimately left it. In this way, the periods for the head, intermediate, and tail car entering the crosswind region were 1.100-1.609 s, 1.409-1.913 s, and 1.713-2.223 s, respectively, and they exited the region at 3.500-4.010 s, 3.810-4.313 s, and 4.113-4.624 s, respectively. As shown in Figure 7a-c, the lateral force of different cars showed great differences. When there was no wind barrier, the lateral force received from the head car to the tail car decreased in order. The \(c_{s}\) value of the head car in the crosswind area without a wind barrier kept increasing, and the growth rate was the fastest when it just entered this area due to the increase in the blocking area to the crosswind. When it left the crosswind area, the \(c_{s}\) value quickly dropped to 0, which was the same as before entering the region. Wind barrier of different heights gave significant changes to the vehicle's aerodynamic coefficients: among them, a 2 m-high wind barrier significantly reduced the lateral force of the head car when it passed through the crosswind area, and a 4 m-high wind barrier gave the head car a \(c_{s}\) value of almost 0, while the 6m-high windshield exhibited excessive wind protection, causing the head car to receive a reverse lateral force. Although the wind barriers brought smaller lateral forces, the wind barrier ends essentially changed the local flow pattern, which was reflected in the apparent fluctuations in the aerodynamic  
Figure 6: The distribution of the pressure on the train surface obtained by the present and previous studies. coefficients when the train entered and exited the wind barrier, especially for the leaving time. For the intermediate car, the 2 m-high wind barrier showed a good windproof effect, while the higher wall (4 m- and 6 m-high) caused the intermediate car to obtain opposite lateral forces. Due to the existence of the wind barriers, the tail car was subjected to a significant sudden change in lateral force when entering and leaving the crosswind region, and the amplitude was much larger than that without a wind barrier.