Design method of the variable cross-section tunnel focused on improving passenger pressure comfort of trains intersecting in the tunnel

Dramatic pressure changes on train surfaces will propagate into carriages through train gaps when two trains intersect in a tunnel, which impacts passenger pressure comfort and even threatens the safety of passengers. An RNG k-ε turbulence model and sliding mesh method are used for a numerical simulation, and the results of a moving model test are adopted for the reliability of the numerical simulation. The alleviation of the interior pressure variations of a train in a variable cross-section tunnel is investigated, in which the tunnel constitutes a reduced section (the cross-sectional area is 70 m2) in the middle and two standard sections (the cross-sectional area is 100 m2 with length L) at both ends. The results indicate that when trains that include 16 carriages intersect in the variable cross-section tunnel with a length of 1450 m at 350 km/h, the interior pressure variations are alleviated with a certain L, which compared to a tunnel with only a standard section. The alleviation effect is optimal when L = 420 m, in which the maximum interior pressure variation on the 3 s time scale for the whole train decreases by 11.24%, and that of carriage 9 decreases by 13.37%. Meanwhile, the amount of tunnel excavation decreases by 12.6%. The rational design of a variable cross-section tunnel can effectively alleviate the interior pressure variations of trains intersecting in the tunnel, thus improving passenger pressure comfort. It can also reduce the construction cost of the tunnel, with significant economic and social benefits.