## 4 Results
### Flow Field and Train Surface Pressure  
Figure 9 shows the distribution of the dimensionless velocity \(U\) and the streamlines projected on the y-z plane at the middle length of the head car downstream various wind barriers. Here, the value of \(U\) can be calculated as:  
\[U=\frac{u}{V}, \tag{7}\]  
where \(u\) is the velocity of the flow in the domain obtained by the numerical result. This comparison was based on the time when the train arrived in the middle of the crosswind region. As the height of the wind barrier increased, its blocking effect on the crosswind became greater, and the airflow acted less directly on the train but moved up and down under the guidance of the wall. When there was no wind barrier, the speed distribution around the vehicle was almost symmetrical with a slight yaw angle, and the existence of the windshield broke this symmetry. As the height of the wind barrier increased, the higher speed region at the bottom of the train body gradually moved from the leeward side to the \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Coefficient**} & \multirow{2}{*}{**Car**} & \multicolumn{4}{c}{**Entering**} & \multicolumn{4}{c}{**Exiting**} \\ \cline{3-10}  & & **200 km/h** & **250 km/h** & **300 km/h** & **350 km/h** & **200 km/h** & **250 km/h** & **300 km/h** & **350 km/h** \\ \hline \multirow{3}{*}{\(c_{s}\)} & Head & 0.993 & 0.653 & 0.441 & 0.312 & 1.744 & 1.222 & 0.925 & 0.723 \\  & Intermediate & 0.604 & 0.314 & 0.219 & 0.097 & 0.852 & 0.693 & 0.426 & 0.279 \\  & Tail & 0.206 & 0.126 & 0.137 & 0.099 & 0.417 & 0.329 & 0.226 & 0.122 \\ \hline \multirow{3}{*}{\(c_{l}\)} & Head & 0.603 & 0.227 & 0.092 & 0.041 & 0.830 & 0.882 & 0.574 & 0.324 \\  & Intermediate & 0.790 & 0.633 & 0.370 & 0.092 & 1.253 & 0.484 & 0.606 & 0.533 \\  & Tail & 0.649 & 0.500 & 0.419 & 0.325 & 0.951 & 0.914 & 0.393 & 0.253 \\ \hline \multirow{3}{*}{\(c_{M_{z}}\)} & Head & 0.111 & 0.075 & 0.050 & 0.034 & 0.233 & 0.142 & 0.110 & 0.086 \\  & Intermediate & 0.069 & 0.032 & 0.022 & 0.005 & 0.117 & 0.094 & 0.047 & 0.029 \\  & Tail & 0.038 & 0.013 & 0.002 & 0.004 & 0.055 & 0.037 & 0.032 & 0.019 \\ \hline \multirow{3}{*}{\(c_{M_{y}}\)} & Head & 0.098 & 0.019 & 0.014 & 0.019 & 1.112 & 0.579 & 0.238 & 0.132 \\  & Intermediate & 0.347 & 0.193 & 0.096 & 0.062 & 0.508 & 0.520 & 0.532 & 0.460 \\  & Tail & 0.699 & 0.438 & 0.223 & 0.156 & 0.717 & 0.485 & 0.331 & 0.111 \\ \hline \multirow{3}{*}{\(c_{M_{z}}\)} & Head & 1.555 & 1.117 & 0.772 & 0.562 & 2.902 & 2.063 & 1.780 & 1.425 \\  & Intermediate & 0.167 & 0.119 & 0.116 & 0.060 & 0.597 & 0.485 & 0.305 & 0.199 \\ \cline{1-1}  & Tail & 1.267 & 0.993 & 0.678 & 0.517 & 1.029 & 0.837 & 0.655 & 0.499 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Peak-to-peak values of the aerodynamic coefficients when each car entered and left the crosswind region with different running speeds. upwind side of the train. Under the protection of the 2 m high wind barrier, a low-speed region caused by the vortex was formed near half the height of the leeward side of the train. The height and scale of this vortex also increased with the height of the wind barrier, as shown in Figure 9b,d. There was also a lower speed in the area between the windshield and the car body. The high-speed area on the top of the train body only existed in the working condition where the wind barrier was less than 2 m.  
Figure 10 shows the pressure distribution on the surfaces of the train when it was located in the same position as Figure 9 from four different perspectives. The pressure distribution on the windward side of the train is shown in Figure 10a. When the train was running without the protection of a wind barrier, the windward side of the nose of the head car obtained the largest positive pressure area, and wind barriers in different heights significantly reduced the area, and there was little difference among these cases with wind barriers.