## 3 Results, Analysis, and Discussion  
### Transient Aerodynamic Forces  
Figure 7 shows the aerodynamic forces and moment variations of each car along the WT. The time mark shows the time at which each car passed the WT region. The aerodynamic coefficients exhibited sudden changes in the region of the WT, and the impact of this change was delayed after the WT. In particular, as indicated by the dashed circle in each figure, there was a sudden increase in the values of \(C_{Fy}\), \(C_{Fz}\), and \(C_{Mx}\) for each car, although there was a certain distance between this change position and the WT region. The impact of the WT occurred at about \(t^{*}=38\) for the head car, at about \(t^{*}=40\) for the middle car, and at about \(t^{*}=50\) for the tail car. After the impact of WT, the aerodynamic performance recovered to a relatively steady state in the cutting after approximately \(t^{*}=85\) for the head car, \(t^{*}=90\) for the middle car, and \(t^{*}=100\) for the tail car. Therefore, the continuous impact time of the WT was approximately \(\Delta t^{*}=47\), \(\Delta t^{*}=50\), and \(\Delta t^{*}=50\) for the head car, middle car, and tail car, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{\(C_{Fy}\)} & \multicolumn{3}{c}{\(C_{Fz}\)} \\ \cline{2-7}  & **Head Car** & **Middle Car** & **Tail Car** & **Head Car** & **Middle Car** & **Tail Car** \\ \hline Test & 1.932 & 0.942 & 0.302 & 1.999 & 1.464 & 1.198 \\ Numerical & 2.010 & 0.957 & 0.312 & 2.012 & 1.480 & 1.253 \\ Error & 4.04\% & 1.59\% & 3.31\% & 0.65\% & 1.09\% & 4.59\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of the side and lift force coefficients between the wind tunnel tests and simulations under a crosswind at a yaw angle of 19.8\({}^{\circ}\).  
Figure 7: Aerodynamic forces and moment variation along the WT: (**a1–a3**) \(C_{Fy}\) of head car, middle car and tail car, respectively, (**b1–b3**) \(C_{Fz}\) of head car, middle car and tail car, respectively, and (**c1–c3**) \(C_{Mx}\) of head car, middle car and tail car, respectively.  
The impact times of the WT on each car were similar, but the strongest impact occurred on the right-angle structure of the windbreak, as shown in Figure 7. The aerodynamic forces changed from a minimum to a maximum and then dropped to the minimum value. The transient time \(\left(\Delta t\right)^{*}\) of the head car was the shortest, followed by the middle car and the tail car. With respect to the peak-to-peak values of \(C_{Fy}\), \(C_{Fz}\), and \(C_{Mx}\) around the right-angle windbreak region, that of the head car was significantly larger than those of the middle car and the tail car. This indicates that the impact of such a WT was more significant for the head car.  
Furthermore, as shown in Table 3, in the flat ground and cutting position, the value of \(C_{Fy}\) for each car was negative, whereas \(C_{Mx}\) had positive values. This indicates that the backflow was dominant in the flat ground and cutting positions. However, in the WT region, not only was the original steady state broken by the sudden peak value, but the action directions of the aerodynamic loads were opposite to those in the flat ground and cutting positions.