Optimizing cross-sectional area of tunnel entrance hood for high speed rail

Abstract A micro-pressure wave (MPW) is radiated from the tunnel exit when a train enters a tunnel at high speed. The MPW causes infrasound and audible noise near the tunnel portal; hence, it must be reduced for environmental reasons. A hood with openings is a typical countermeasure. The openings must be suitably distributed to effectively reduce the MPW. The optimum distribution depends on the shape of the train nose and its velocity; therefore, it needs to be readjusted, and the hood sometimes needs to be extended when the train velocity increases or a new type train is put into operation. This study reports on numerical studies and model experiments to investigate the effective composition of an unvented hood because such a hood would eliminate the need to adjust the distribution of the openings according to the train characteristics. The results show that the optimum cross-sectional area of the hood is 2.6 times the cross-sectional area of the tunnel, and its optimum length is 1.8 times the tunnel diameter when the train velocity is 350 km/h, and the train nose length is three to six times the train radius. Finally, the unvented hood is economically advantageous compared with the currently used hood.