Abstract: Metro long-gradient interval tunnel fire faces problems such as difficult evacuation of people, low smoke exhaust efficiency, and difficult rescue. Relying on the Longquanshan Tunnel Project, segmental modelling was carried out based on FDS, and the effect of fixation-movement combination of smoke control was investigated by analyzing the distance between the mobile fan and the train, D, and the fan axial height, H. The results show that the maximum ceiling temperature for a 10.5 MW fire at the bottom of the train is not higher than 100 °C under ventilated conditions; The mobile fan with an air output of 70 000 m3/h can effectively co-operate with ventilation to cut down smoke back-layering, and compared with fixed mechanical ventilation, the length of smoke back-layering can be shortened up to 189.2 m, which increases the safety space for firefighting and rescue in the upstream； The maximum ceiling temperature is controlled between 76~79 ℃ under fixation-movement combination; The wind speed in the tunnel section increases with the increase of H and the speed in the section is 2.43 m/s, with H=3.5 m; When D=100 m, H=3.5 m, the synergistic effect is the best, which provides reference for the design of rescue equipment of metro.

Key words: numerical simulation, metro fire, long-sloped interval tunnel, mobile fan, longitudinal ventilation, ceiling temperature