# Aerodynamic Characteristics When Trains Pass Each Other in High-Speed Railway Shield Tunnel
## 4 Results and Discussion  
### Pressure Wave Characteristics in Tunnels  
Figure 7 shows the pressure-time history curve of the point of measurement on the wall at the center of the shield tunnel. The point of measurement was located on the tunnel wall of the left track at a height of 1.5 m from the track surface. The train travel speed was \(350\) km/h. Figure 7 shows that when a train passed through the shield tunnel, the positive and negative peak pressure loads at the central point of measurement of the lining structure were \(1878.5\) and \(-3057.2\) Pa, respectively. After exiting the tunnel, they were \(2445.9\) and \(-2106.2\) Pa, respectively. The pressure load ranges when the train passed through the tunnel and after it exited were \(4935.7\) and \(4552.1\) Pa, respectively. When the two trains met at the center of the tunnel, the positive and negative peak pressure loads at the central measuring point of the lining structure were \(4149.2\) and \(-6319.9\) Pa, respectively. After exiting the tunnel, it was \(4519.3\) and \(-3794.3\) Pa, respectively. The pressure load ranges of the train passing through the tunnel and after exiting the tunnel were \(10469.1\) and \(8313.6\) Pa, respectively. Thus, the trains met at the center of the tunnel at a constant speed, and the range of the aerodynamic pressure load changes during the passing phase of the train and after the train exited the tunnel were \(2.12\) times and \(1.83\) times that of a single vehicle, respectively. After the intersecting trains exited the tunnel, the pressure load range in the tunnel was still \(1.68\) times the pressure load range when a train was traveling in the tunnel. This fully showed that the intersection of the two trains had a greater impact on  
Figure 5: Mobile model test device: (**a**) double-track tunnel model and (**b**) high-speed train model CRH380A. Figure 6: Comparison of dynamic model test and simulation results. the aerodynamic load of the tunnel, which further demonstrated the need to study the aerodynamic loads of the intersecting pressure waves in a high-speed railway tunnel. When the two high-speed trains entered the tunnel at the same time, the compression wave generated by the front of the car and the expansion wave generated by the rear of the car propagated and superimposed in the tunnel, after which they were reflected at the tunnel port. This caused the pressure distribution in the tunnel at the time of the intersection to become more complicated. Figure 8 shows the propagation of the pressure wave and the corresponding change when the trains met at the midpoint of the tunnel, in which Figure 8a is a schematic diagram of wave system propagation; Figure 8b is a pressure time history diagram. The horizontal line in Figure 8a represents the position of the sensor on the tunnel lining. The bold black and blue lines represent the positions of the head and tail of train A at different times, respectively, and the bold red and pink lines indicate those of train B. The relatively thin black solid line, blue solid line, red solid line, and pink solid line represent the compression waves generated by trains A and B in the tunnel, which are labeled with the letter C, e.g., \(\mathrm{C_{AH}}\), \(\mathrm{C_{BH}}\), \(\mathrm{C_{AH1}}\), \(\mathrm{C_{BH1}}\), \(\mathrm{C_{BT}}\), and \(\mathrm{C_{AT}}\). Similarly, the relatively thin black dotted line, blue dotted line, red dotted line, and pink dotted line represent the expansion waves generated by the head of train A, the head of train B, the tail of train A, and the tail of train B in the tunnel, respectively, which are labelled with the letter E, e.g., \(\mathrm{E_{AT}}\), \(\mathrm{E_{BT}}\), \(\mathrm{E_{AT1}}\), \(\mathrm{E_{BTI}}\), \(\mathrm{E_{AH}}\), and \(\mathrm{E_{BH}}\). The compression and expansion waves generated in the tunnel are represented by green solid lines and dashed lines, respectively, when trains A and B exited the tunnel. Compression or expansion waves propagate along the tunnel.