Study On Fire Flue Gas Movement Mechanism Of U-type Tunnel

The feasibility of FDS in fire simulation was verified by comparing the experimental values of the small size test platform with the simulated values of FDS.In order to study the movement mechanism in U-type tunnel,the FDS was used to simulate fire scene based on the importance of fire smoke flow theory.The flue gas temperature,the flue gas velocity and direction,the height of flue gas and the concentration of CO in the tunnel were studied under the conditions of different natural ventilation rate,different slope and different fire power.The following conclusions were obtained:(1)In the U-type tunnel,the phenomenon of flue gas countercurrent was more serious than the other two tunnel models.In the U-type tunnel,the natural ventilation rate changes caused four phenomena: it could make the smoke spread to the downstream exports but the final smoke is still completely countercurrent;it could make the final flue gas from the downstream exports,but the initial flue gas could spread to the upstream entrance;it can make the phenomenon of countercurrent flue gas,but could not be discharged from the upstream entrance;it could enable smoke not to appear countercurrent.(2)After the fire source was extinguished,the U-type tunnel could discharge the flue gas more quickly than the horizontal tunnel,reduce the temperature,and the flue gas discharge direction was consistent with the final discharge direction of the flue gas in the stable stage of the fire power.(3)In the fire source power stabilization stage,the slope ?=45°is a critical value for the upstream survey data.The increase of the slope affected the heating time,the flue gas layer thickness and the CO concentration change.The change of the maximum temperature caused by the increase of the slope was inconsistent with the change of the temperature rise time caused by the change of the slope.(4)The downstream of the U-shaped tunnel was the same as the slopeof the upstream tunnel,which was symmetrical about the center.If the flue gas must be discharged from the downstream outlet,the location of the fire for the spread of smoke,ventilation and smoke options had a decisive impact.