## 4 Results and Discussion
### Effects of the Curved Wind Barrier on the Aerodynamic Characteristics of the Train-Bridge System
On the basis of the above research, after C3 wind barriers with different porosities are installed on the bridge (wind attack angle \(\alpha=0^{\circ}\)), the variations of aerodynamic three-component coefficients of the train and pressure coefficients of the train's section under different train-bridge combinations are compared. There are four cases for the tested train  
Figure 12: Velocity streamline of the train-bridge system: (**a**) without a wind barrier, (**b**) with the C1 wind barrier, (**c**) with the C2 wind barrier, (**d**) with the C3 wind barrier, (**e**) with the C4 wind barrier. in three different train-bridge combinations; the schematic diagrams of the four cases are shown in Table 2.  
Figure 13: Aerodynamic coefficients of the train and bridge with different curved wind barriers: (**a**) drag coefficient of the train, (**b**) drag coefficient of the bridge, (**c**) lift coefficient of the train, (**d**) lift coefficient of the bridge, (**e**) moment coefficient of the train, and (**f**) moment coefficient of the bridge. Figure 14a-c presents the variations of aerodynamic three-component force coefficients of the train with the porosity of the wind barrier under different train-bridge combinations. The three-component coefficients of the train increase with the increase of the wind barrier's porosity. When there is only one train on the bridge, the test train of Case2 is in the low-speed wake generated by the front edge of the bridge and the wind barrier of windward side, and the aerodynamic coefficients of the test train in Case2 is significantly smaller than Case1. When there are trains on both the windward and leeward sides of the bridge, the train on the leeward side of the bridge will cause aerodynamic interference to the train on the windward side. The negative pressure on the leeward surface of the train on the windward side of the bridge will decrease slightly, resulting in the aerodynamic coefficients of the test train in Case3 to be slightly lower than Case1. The test train of Case4 is completely immersed in the wake of the curved wind barrier and the train on the windward side of the bridge. The aerodynamic coefficients are very small, especially the drag coefficient, which is a negative value close to 0. With the increase of the porosity of the curved wind barrier, the drag coefficient slightly increases, but it is still negative. Figure 15 shows the influence of C3 wind barriers with different porosities on the wind pressure distribution on the train's section (the pressure taps on the section of the train are shown in Figure 11a). When there is only one test train on the bridge (Case1, Case2), as present in Figure 15a,b, with the increase of the porosity of wind barrier, the wind pressure on the windward surface of the test train gradually increases from negative to positive, and the distribution along the vertical direction is hardly changed. Under the same test conditions, the positive pressure on the windward side and the negative pressure on the roof of the test train in Case1 are significantly greater than those in the test train in Case2, and the wind pressure on the leeward surface and bottom of the test train under the two cases are almost the same. This can explain the reason why the aerodynamic coefficients of the test train of Case1 are significantly greater than that of the test train of Case2, as shown in Figure 14. \begin{table}
\begin{tabular}{c c} \hline \hline
**Case** & **Schematic Diagram** \\ \hline Case1 & \\ Case2 & \\ Case3 & \\ Case4 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Schematic diagrams of the four cases for the tested train. When there are trains (Case3, Case4) on both sides of the bridge, as shown in Figure 15c,d, the location of the test train has a significant impact on its wind pressure distributions.