| In recent years,with the rapid development of social economy,the tunnel mileage has been increasing,which has brought great convenience to the flow of people and goods,but also generated a series of safety problems,among which fire accidents occur from time to time.When a fire breaks out in a tunnel,if it cannot be controlled in time,it will not only endanger the life and safety of the trapped people,cause huge property losses,but also have a negative social impact.Studies have shown that longitudinal ventilation can effectively reduce the concentration of high-temperature flue gas in the tunnel,but will provide fresh air for the fire source,and the fine water mist has good fire extinguishing and cooling effects,so it is of great significance to study the control effect of longitudinal wind and water mist on the flue gas and temperature in the tunnel.In this paper,a 1:10 scale small-size tunnel platform is constructed,and the method of combining small-scale experiment and numerical simulation is used to study the control effect of fine water mist on the temperature field,smoke field and visibility of rectangular section tunnel during fire under the action of longitudinal wind.Firstly,the results of the water mist fire extinguishing experiment in the open space and the water mist fire extinguishing experiment in the tunnel under the same working conditions are analyzed,and it is concluded that: 1)When extinguishing fire under both conditions,the average fire extinguishing time decreases first and then increases with the increase of the power of the fire source,but when extinguishing the fire in the tunnel,the average fire extinguishing time is shortened.2)The average cooling rate of water mist50 cm above the fire source during fire extinguishing in the tunnel is lower than the average cooling rate of fire extinguishing in open space under the same working conditions;The average cooling rate of water mist at 10 cm above the fire source is higher than the average cooling rate when extinguishing fires in open spaces under the same working conditions.3)When the water mist in the tunnel is extinguished,a large amount of smoke will be collected around the fire source due to the suction effect,which will destroy the stability of the flue gas layer and accelerate the process of filling the tunnel with the flue gas.Secondly,the small-scale simulation of water mist fire extinguishing in the tunnel is carried out,and the experimental results are compared with the experimental results in terms of roof temperature,temperature above the fire source,and flue gas movement law,and the results show that the results of FDS numerical simulation can be effectively applied to the research of water mist fire extinguishing in the tunnel.Thirdly,the influence of longitudinal wind speed on the water mist action area is carried out,and the results show that when the flow coefficient of the nozzle is the same,the actual width of the water mist in the tunnel increases with the increase of the longitudinal wind speed.Finally,the experiments and numerical simulations of the fire performance of the rectangular section tunnel under the action of longitudinal wind are carried out,and the results show that: 1)Adding longitudinal ventilation can effectively increase the average cooling rate of the fine water mist,and the flue gas is controlled downstream of the tunnel after turning on the fine water mist for a period of time,the greater the wind speed,the shorter the time required to control the flue gas downstream of the tunnel.2)When the ignition power Q≤24k W is under small size conditions,the optimal combination of longitudinal wind speed and flow coefficient of water mist nozzle is V=0.6m/s,K=1.1.3)When the fire source power of rectangular section tunnel under full-scale conditions is20 MW,the longitudinal wind speed with good control effect on flue gas field and temperature field is 3m/s.Figure 90 Table 18 Reference 77... |
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