# Aerodynamic Characteristics When Trains Pass Each Other in High-Speed Railway Shield Tunnel
## 5 Conclusions  
The three-dimensional, compressible, and unsteady RANS method was used to study the aerodynamic characteristics of high-speed trains when they met in a shield tunnel. By comparing the numerical calculation results with dynamic model tests, the reliability of the numerical simulation was verified. The conclusions were as follows:  
1. Through detailed analysis of wave diagrams and pressure cloud diagrams of high-speed trains meeting in a shield tunnel, the mechanism of the pressure changes on the train surface and lining structure during the intersection of the two trains was explained intuitively and clearly.
2. Based on the analysis of the aerodynamic effects of different tunnel lining structures, it was revealed that the shield tunnels were affected by bolt holes, the tunnel wall  
Figure 17: Aerodynamic lateral force on the surface of the train: (**a**) aerodynamic lateral force versus time and (**b**) maximum aerodynamic lateral force versus train speeds.  
Figure 18: Maximum aerodynamic lateral force on the surface of the train at different intersection positions in the tunnel.  
roughness, and nonlinear effects, and the pressure amplitude decayed faster. When the high-speed trains met in the middle of the tunnel, the positive and negative peaks of the micro-pressure wave of the shield tunnel were reduced by 10.78% and 4.39%, respectively, compared with the micro-pressure wave of the molded lining tunnel. Therefore, the use of a shield tunnel lining can reduce the micro-pressure wave at the exit of the tunnel.
3. After the train left the tunnel, the positive and negative peak attenuation rates of the shield tunnel were higher than the positive and negative peak attenuation rates of the molded lining tunnel. In the first three fluctuation cycles, the pressure decay rates of the positive and negative peaks became gradually larger, and the maximum pressure decay rate in the shield tunnel could reach 57.8%. In the subsequent period of pressure fluctuations, the pressure decay rate in the molded lining tunnel was maintained at 4.1-9.3%, while that in the shield tunnel was maintained at 7.8-15.3%.
4. The maximum positive and negative pressure values on the tunnel lining structure when high-speed trains intersected in the middle of the tunnel were both located at the central measurement point of the tunnel, and the maximum pressure at this measurement point was significantly greater than that at other intersections in the tunnel. The values of the micro-pressure waves 20 and 50 m outside the tunnel exit, caused by different intersection positions, could meet the specification requirements.
5. The train speed had a greater influence on the aerodynamic drag and aerodynamic lateral force on the surface of the train, while different intersection positions and different tunnel lining structures had relatively little influence on the aerodynamic drag and aerodynamic lateral force.  
[PERSON] conceived and designed the analysis, collected and analyzed data, and wrote and revised the paper; [PERSON] conceived and designed the analysis, provided funding, and revised the paper; [PERSON] provided guidance on the numerical simulation software; [PERSON] wrote and edited the paper and provided supervision. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant numbers [51878038, 51678036]. The authors are grateful to all the study participants.  
Data sharing not applicable.  
The authors gratefully acknowledge the support of the National Natural Science Foundation of China [51878038, 51678036]. The funder had no role in the experimental design, model establishment, data analysis, manuscript writing, or decision to submit this article for publication. The authors thank the anonymous reviewers who provided valuable suggestions that improved the manuscript.  
The authors declare no conflict of interest.