## 3 Validation of the Numerical Simulation  
The scaled 1:40 sectional model wind tunnel tests are carried out in the high-speed test section of the high-speed railway wind tunnel test system in Central South University, China. The test results are compared with the numerical simulation results to verify the accuracy of the numerical simulation. The schematic diagram of the wind tunnel and the high-speed test section are shown in Figure 4a,b. The dimensions of the high-speed test section are 15 m \(\times\) 3 m \(\times\) 3 m (length, width, and height). The oncoming flow velocity can be continuously adjusted within the range of 0-94 m/s. All tests in this study are conducted in a uniform flow field with a wind speed of 10 m/s, and the turbulence intensity is less than 0.5%.  
The aerodynamic forces of the train and bridge are tested after C1 wind barriers with respect to three different porosities (0%, 20%, and 40%), which were installed on both sides of the bridge. The geometric scale ratio of the model is 1:40, and the dimensions of the train, bridge, and wind barrier segment models are described in Section 2.1. The calculated  
Figure 3: Schematic diagram of the computational mesh: (**a**) global view of the mesh, (**b**) surface mesh of the model.  
maximum blockage ratio is 2.21%, which meets the requirements of wind tunnel tests. In order to ensure the stiffness of segment models in the wind environment, as present in Figure 5a, the train, bridge, and wind barrier models are made of steel skeleton plastic, steel skeleton wood, and plastic materials, respectively. The wind tunnel test system is shown in Figure 5b. The IFS six-component dynamic balance used in these tests is produced by Japan's NITTA company with a force measurement resolution of 0.02 N, a sampling frequency of 1 kHz, and a sampling duration of 30 s. The aerodynamic force measured by the dynamic force balance can be converted by formulas (8)-(10) to obtain the aerodynamic three-component force coefficients of the train and bridge.  
The numerical models with the same geometric dimensions as the above-mentioned wind tunnel tests are established. The calculation conditions are consistent with the wind tunnel tests. The aerodynamic coefficients of the train and bridge after setting C1 wind barriers with three different porosities (0%, 20%, and 40%) on both sides of the bridge are simulated. The results of the wind tunnel tests and numerical simulations both show that with the gradual increase of the porosity of C1 wind barrier, the aerodynamic force of the train increases gradually, while the aerodynamic force of bridge decreases gradually. The two results are in good agreement and show consistent trends. The comparison of the wind tunnel tests and detailed numerical simulation results is presented in Table 1. It can be seen from Table 1 that the maximum error of the aerodynamic coefficients of the train and bridge obtained by wind tunnel tests and numerical simulations is less than 7%. The errors are all within a reasonable range, which can verify the reliability of the numerical simulation.  
Figure 4: Schematic diagram of whole wind tunnel structure and high-speed test section: (**a**) schematic of the wind tunnel, (**b**) high-speed test section.  
Figure 5: Wind tunnel test: (**a**) model of the train, bridge, and wind barrier, (**b**) wind tunnel test system.