Study On Characteristic Of Fire Smoke Flow And Smoke Control Method In Spiral Tunnel Of Highway

Once a fire occurs in the spiral tunnel,the high-temperature smoke constantly collides with the wall to form eddy current.The wall friction causes the smoke velocity near the wall to be significantly lower than that at the center,and the smoke discharge is difficult.The major fire accident in Yanhou tunnel reveals the dynamics of fire scale growth.There is a deviation between the tunnel smoke spread law and control mode based on the static fire scale and the actual demand of the tunnel.Therefore,it is necessary to determine the dynamic fire scale of highway tunnel,explore the characteristics of fire smoke spread and formulate supporting fire extinguishing facilities to realize automatic fire extinguishing.Based on the above problems,this paper adopts research methods such as data investigation,theoretical analysis and numerical simulation to study the dynamic fire scale,smoke spread law,fire critical wind speed and longitudinal ventilation coupled water mist fire extinguishing mechanism of highway spiral tunnel with Jinjiazhuang long spiral tunnel of Yanchong Expressway as the support project.The main results are as follows:1.Through literature research,theoretical analysis and numerical simulation,the relationship between driving speed and radius threshold of highway spiral tunnel is established,and the fire combustion and ignition mechanism of highway tunnel are proved.The prediction formula of ignition range changing with curvature is obtained,and the determination method of dynamic fire scale of highway tunnel based on risk analysis is proposed.The growth curve of dynamic fire scale is given,and the calculation formula of smoke production based on dynamic fire scale is obtained.2.Through theoretical analysis and numerical simulation,the calculation formula of smoke production rate based on the heat release rate curve of dynamic fire scale is given.The influence of curvature and slope on the flow field,temperature field and visibility field of spiral tunnel is revealed.The prediction formula of maximum temperature of spiral tunnel vault with curvature under different wind speeds is obtained.The critical curvature of smoke spread in spiral highway tunnel is proved to be similar to that in straight tunnel.3.Through literature research,theoretical analysis and numerical simulation,the correction formula of critical wind speed based on curvature and slope of spiral tunnel is given,the influence of water mist on critical wind speed of spiral highway tunnel is analyzed,and the theoretical model of critical wind speed prediction under water mist of spiral highway tunnel is established.4.Through theoretical analysis and numerical simulation,the main fire extinguishing mechanism of water mist under the action of longitudinal ventilation was revealed.The fire extinguishing effect of longitudinal ventilation coupled with water mist under the action of curvature,starting time of longitudinal ventilation system and longitudinal ventilation wind speed was analyzed,and the recommended values of longitudinal ventilation and water mist characteristic parameters of super-long spiral tunnel were given.The above results can provide basis for fire smoke control design of long spiral highway tunnel.