Influence of variable cross-section on pressure transients and unsteady slipstream in a long tunnel when high-speed train passes through

When constructing a long undersea tunnel, cross-sectional area of some parts of the tunnel will be changed to strengthen the tunnel or save construction costs, which will cause a change in aerodynamic characteristics of the tunnel. By comparing variable cross-section(VCS) tunnel and constant cross-section (CCS) tunnel, the influence of abrupt cross-section on pressure transients and slipstream in the long tunnel was studied. The RNG k-epsilon turbulence model was adopted for numerical simulation, which was validated by the moving model test. The results show that the closer it to the abrupt cross-section, the larger the difference between the positive peak pressure of the VCS tunnel and that of the CCS tunnel, reaching a maximum of 7.63% at 5.43 km. The difference in slipstream velocity in the longitudinal direction between the two tunnels can reach 18.7% at most, but it is almost the same in the other two directions. In addition, the impact of the abrupt section on slipstream in different areas of the tunnel is different. This research has an important reference value for parameter design of long variable cross-section tunnel and layout of auxiliary facilities in tunnel.