Fire Concentration Field And Evacuation Simulation Of Complex Urban Tunnels

The design structure of urban underground tunnels is different,their personality is very prominent,and the tunnels are mostly connected with other public facilities,so there are obvious differences in fire accidents.There is no uniform evacuation plan for people under fire conditions for design and selection.On the basis of collecting and analyzing the data of tunnel fire cases at home and abroad,and relying on a complex urban road tunnel with four lanes and multi-ramps,this paper simulates the scale velocity field,concentration field and temperature field of 5MW,10 MW and 20 MW tunnel fire based on the fire dynamics simulation software FDS.Based on the literature value,the correctness of the selection of simulation methods and the setting of parameters is verified.At the same time,on the basis of FDS simulation results,the evacuation simulation software Pathfinder is used to simulate and analyze the evacuation situation under tunnel fire conditions.According to the results of simulation analysis,some suggestions are provided for the establishment of evacuation plan under tunnel fire conditions.According to the specific conditions of the tunnel,based on the simulation results,the main conclusions are as follows:(1)When the ventilation speed is less than the critical wind speed,the temperature of the downstream section of the fire source decreases exponentially.The closer the fire source is to the tunnel wall,the more concentrated the high temperature area of the tunnel and the smaller the flue gas fluctuation.With the increase of the heat release rate of the fire source in the tunnel,the critical wind speed increases.The recommended critical wind speed for 5MW fire source is v=2m/s,and for 10 MW and 20 MW fire source is v=2.5m/s.(2)The blockage ratio and the setting mode of obstruction will have a great influence on the stratification and temperature distribution of flue gas.The greater the blockage ratio,the greater the influence on the flue gas layer.The influence of blocking at the upstream end of fire source on the flue gas layer is less than that of blocking at the downstream end.(3)The necessary evacuation time of the tunnel is determined by the maximum value of simulated evacuation,that is,the necessary evacuation action time t = 160 s.(4)The fire source and the tunnel entrance will be divided into sections.The closer the fire source is to the tunnel internal entrance,the longer the evacuation distance of some people and the longer the evacuation time.According to the simulation results,the time required for evacuation and the route selected by the people,combined with the FDS simulation results,the most reasonable and efficient evacuation method and the planning of evacuation route are determined.It provides a reference for the study of tunnel evacuation.