## 4 Results and Discussion
### Flow Field Characteristics of HSTs Entering Curved Wind Barriers  
Figure 12 illustrates a comparison of the lateral cross-sectional pressure distribution cloud maps at the center of the head car of a HST before entering a bridge wind barrier and after entering wind barriers with three different porosities (10%, 30%, and 50%). It is obvious that the train is directly exposed to airflow before entering the wind barrier, leading to positive pressure on the windward surface that reaches a maximum value exceeding 120 Pa. Simultaneously, due to airflow separation and acceleration, a high-pressure zone is formed above the train roof, generating a maximum negative pressure of more than \(-\)500 Pa. When the train enters the wind barrier area, the presence of the wind barrier significantly affects the surface pressure distribution. The positive pressure on the windward surface decreases while the negative pressure on the leeward surface increases. Furthermore, the negative pressure on both the train roof and bottom decreases. The degree of pressure variation on the train surface depends on the porosity of the curved wind barrier, with a smaller porosity resulting in a greater pressure variation. The process of a HST entering a wind barrier involves intense variations in aerodynamic pressure on the different surfaces of the train. This leads to a significant difference in pressure between the windward and leeward surfaces, as well as the top and bottom of the train, ultimately causing a sudden change in the aerodynamic load of the HST. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Running**} & & & \multicolumn{2}{c}{\(\Delta C^{\prime}_{\text{max}}\)} & & \\ \multicolumn{2}{c}{**Speed**} & **Carriage** & & **Enter** & & **Exit** & \\ \multicolumn{2}{c}{**(km/h)**} & & \(\mathbf{C_{D}}\) & \(\mathbf{C_{L}}\) & \(\mathbf{C_{M}}\) & \(\mathbf{C_{D}}\) & \(\mathbf{C_{L}}\) & \(\mathbf{C_{M}}\) \\ \hline \multirow{3}{*}{200} & Head & 0.6171 & 0.3506 & 0.1086 & 0.6631 & 0.3229 & 0.0966 \\  & Middle & 0.1606 & 0.1240 & 0.0277 & 0.1451 & 0.1271 & 0.0254 \\  & Tail & 0.1501 & 0.0926 & 0.0287 & 0.1341 & 0.0530 & 0.0323 \\ \hline \multirow{3}{*}{250} & Head & 0.6013 & 0.2627 & 0.1003 & 0.5827 & 0.2583 & 0.0899 \\  & Middle & 0.1249 & 0.1667 & 0.0147 & 0.1178 & 0.2088 & 0.0133 \\  & Tail & 0.1057 & 0.0977 & 0.0249 & 0.0963 & 0.0874 & 0.0289 \\ \hline \multirow{3}{*}{300} & Head & 0.5794 & 0.2220 & 0.0923 & 0.5269 & 0.1837 & 0.0797 \\  & Middle & 0.0829 & 0.1657 & 0.0106 & 0.0791 & 0.1871 & 0.0094 \\  & Tail & 0.1011 & 0.0857 & 0.0171 & 0.1146 & 0.0551 & 0.0183 \\ \hline \multirow{3}{*}{350} & Head & 0.5577 & 0.1738 & 0.0850 & 0.4905 & 0.1470 & 0.0731 \\  & Middle & 0.0718 & 0.1573 & 0.0080 & 0.0724 & 0.1591 & 0.0073 \\ \cline{1-1}  & Tail & 0.0942 & 0.1013 & 0.0111 & 0.1116 & 0.0750 & 0.0111 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Amplitude of the rate of changes in aerodynamic load coefficients for the HST passes through the curved wind barrier at different running speeds. Figure 12: Pressure distribution of the lateral cross-section of the head car: (**a**) before entering the wind barrier area, (**b**) when entering the wind barrier area with a porosity of 10%, (**c**) with a porosity of 30%, and (**d**) with a porosity of 50%. Figure 13 illustrates the velocity streamline diagram of the lateral cross-section of the HST as it enters wind barrier areas with different porosities. Plane 1, Plane 2, and Plane 3 represent the cross-sections at the center positions of the head, middle, and tail cars, respectively. The streamlines are represented by the dimensionless speed \(U/U_{w}\), where \(U\) is the airflow speed near the train and \(U_{w}\) represents the crosswind speed. From Figure 13a, it can be observed that the incoming airflow undergoes separation and acceleration before entering the wind barriers near the leading edge of the bridge, resulting in a slightly higher wind speed around the windward surface of the train compared to the incoming airflow.