Study On Fire Smoke Stratification In Metro Tunnel

The study on the characteristics of tunnel fire smoke flow has important theoretical significance and practical value for the smoke control and evacuation of tunnel fire.At present,the research on the tunnel fire smoke control is mainly focused on the highway tunnel,the railway tunnel,the short merto tunnel and the long merto tunnel with intermediate vertical shafts.In some tunnels cross mountains or rivers,the intermediate vertical shafts can't be set,and it is different from the general tunnel in the fire smoke flow characteristics and smoke control method.There is few research about smoke control strategy on this kind of tunnel,and it is worthy of further study.For the study of long metro tunnels,field-network model is suitable.The key of this method is to determine the interface of field-network model,and the smoke completely settlement point also affects the interface position.When the fire occurs in middle of long metro tunnel without intermediate vertical shaft,the fire smoke exhaust is difficult.So some two-way jet fans need to be installed in the proper place of the tunnel to exhaust the fire smoke,ensuring that the toxic hot gas keep stable stratification and stay in upper air space.At the same time,connecting passages need to be set at a certain distance to evacuate people.And the smoke stratification regularities have a guiding effect on the setting spacing of the jet fans and the contacting passages.Therefore,the study of the smoke stratification is of great significance to the design of smoke exhaust system and the evacuation of the long metro tunnel.Based on summarizing the statistical result of line forms,interval length and cross-section forms in Metro Line 6 in Chongqing,small-scale experiments are carried out,which is a 1/15 scale model tunnel baesd on a typical tunnel,meanwhile,some numerical simulation experiments are carried out based on different cross-section forms of the tunnel.Through the small-scale and numerical simulation experiments,smoke stratification regularities are researched in different heat release rates,longitudinal ventilation velocities and the tunnel cross-section forms in long metro tunnel.The main achievements of this thesis are as follows:1.Put forward the concept of the stable stratification length and the critical stratified velocity.2.The change rules of the fire smoke stable stratification length under different boundary conditions such as the heat release rate,the longitudinal ventilation velocity and the tunnel cross-section form is studied.3.Using the method of dimensional analysis,this paper puts forward the prediction model of the stable stratification length of the fire smoke and the critical stratified velocity in the metro tunnel.4.The position of the interface between the near fire source area and the far fire area in the metro tunnel is discussed,which is aslo the interface between hybrid field-network model.