Smoke Movement And Critical Velocity Of T-intersecting Branch Tunnel Fires

With the continuous development of modern social transportation modes,the tunnels are becoming more and more popular,and the fires in the tunnels have brought new problems and challenges to mankind.In recent years,many major tunnel fire accidents have occurred.These accidents have warned us that although tunnels can bring convenience to people,the safety situation of tunnel fires is becoming more and more serious.If tunnel fires cannot be effectively controlled,Extremely likely to have unpredictable consequences.The branching tunnel is a tunnel with special structure.The flow law of smoke after fire is the same as that of ordinary tunnel.Therefore,it is of great practical significance to carry out research on the smoke movement law of fire in tunnel.This article studies the motion characteristics of smoke in the tunnel and provides appropriate fire protection for the tunnel.In the bifurcation tunnel,the traffic mode can be divided into two types: the diversion of the bifurcation and the confluence of the bifurcation.Based on the two modes of transportation,the cross-flow length,critical velocity and maximum ceiling of the tunnel fire under longitudinal ventilation are respectively Temperature rise was performed on solid scale experiments and numerical simulations.In the experiment,the fire source is located in the branching and connecting area of the branching tunnel,which is used to simulate traffic accidents near the branching point.The numerical simulation is to use the FDS simulator to carry out tunnel modeling and set the required working conditions for operation research.Through the study on the smoke flow characteristics of diverging and bifurcation tunnel fire,it is found that the critical velocity of main road fire in bifurcation tunnel is not affected by the bifurcation angle.Compared with the linear tunnel,the critical wind speed of the bifurcated tunnel is usually less than the critical wind speed model of the existing linear tunnel when the fire source power is small.When the fire source power is large,the critical wind speed of the bifurcated tunnel is close to the current linear tunnel model.Through the study of the critical velocity of the convergent bifurcation tunnel fire,it is found that the critical wind volume decreases with the local decrease of the gradually shrinking main road,the gradually shrinking structure,the bifurcation Angle and the bifurcation structure have no effect on the critical wind volume,and the relationship between the dimensionless critical velocity and the dimensionless heat release rate is similar to the results of the previous linear tunnel.Through the research of this subject,the model formula which is more suitable for the critical velocity of the bifurcation tunnel and the prediction model of critical velocity,flue gas backlayering length and maximum temperature rise under different conditions are obtained,which provides a theoretical basis for longitudinal ventilation of tunnel fire.