Mitigation of micro-pressure wave at 400 km/h railway tunnel exit by oblique enlarged tunnel-hood

Numerical simulations based on the three-dimensional, compressible, unsteady Navier-Stokes equations and the RNG k-ε two-equation turbulence model are used to study the micro-pressure generated by a high-speed train passing through a tunnel at the speed of 400 km/h, and the numerical results are further verified by the moving model test. The effects on the micro-pressure wave at the tunnel exit by the tunnel length, the tunnel-hood length (enlarged section with oblique tunnel portal) and the number of openings holes on the tunnel-hood, are analyzed. Results show that: when the tunnel length is in a certain range, the amplitude of the micro-pressure wave gradually increases with the increase of the tunnel length. The tunnel-hood with an enlarged section of equal cross-section with oblique tunnel portal (30°) at the tunnel entrance can effectively reduce the amplitude of the micro-pressure wave, the alleviative rate of the amplitude of the micro-pressure wave first increases then decreases with the increase of the tunnel-hood length, and the best mitigation effect is achieved when the length of the tunnel-hood is 88.56 m, with an alleviative rate up to 59.2%. The tunnel-hood can further alleviate the amplitude of the micro-pressure wave by opening holes, and the best mitigation effect is achieved when two holes are opened on the tunnel-hood, which results in an alleviative rate of 70.9%. The tunnel-hood proposed in this study can make the amplitude of the micro-pressure wave at the exit of a tunnel with a length less than 5 km meet the national standard. The present findings provide important guidance for the design of tunnel-hoods used in the 400 km/h high-speed railway.