Numerical Simulation Of The Influence Of Fire Source Position On The Limit Height Of Tunnel Shaft Chimney Effect

In today’s rapid economic development,a strong transportation capacity is needed to maintain social development.In order to create a more convenient transportation route in a limited space,the construction of traffic tunnels has become the mainstream.As the number of speed tunnels increases,the frequency of tunnel fires also increases.The space in the tunnel is small,the closure is strong,and the internal structure is complex and changeable.When a fire occurs in a highway tunnel with a shaft,the flame spreads quickly and it is difficult to fight the fire,which will bring great safety threats and economic losses to our people.It will also bring bad effects to the society.Therefore,studying the chimney effect of the shaft in the tunnel is of great significance for fire smoke exhaust.This subject is the Liaoning Provincial Natural Science Foundation project "The influence factors and mechanism of the limit height of the shaft chimney effect"(20180550336).Many scholars at home and abroad have done research on the chimney effect of tunnel fire shafts.It is proposed that the chimney effect has a critical value,but it has not been studied in depth.This paper conducts an in-depth study on this issue,using FDS to simulate the situation in the tunnel after the fire occurs,and study the law of smoke movement in the shaft.At different fire source locations,this critical value is determined by changing the height of the shaft.That is,the limit height of the chimney effect.And get the qualitative influence relationship between it and the location of the fire source,and quantify it.The main content and research results of this paper are as follows:(1)The chimney effect of highway tunnel shafts has a critical value.After a fire occurs,the speed of smoke in the tunnel shaft will increase with the height of the shaft within a certain shaft height.When the height increases to a certain height,the speed of smoke in the shaft reaches the maximum.After reaching the maximum,as the height of the shaft increases,the velocity of the flue gas in the shaft decreases.The height of the shaft corresponding to the maximum velocity of the flue gas is called the limit height of the shaft chimney effect.(2)When the shaft cross section is square and other conditions(fire source power,ventilation method,shaft section size and shaft inner wall material)remain unchanged,As the distance between the fire source and the centerline of the shaft increases,the limit height of the shaft chimney effect continues to decrease.When the fire source power is 8MW,Available =-50.78 ln()+ 423.78(x represents the distance between the fire source and the centerline of the tunnel shaft,y represents the ultimate height of the shaft)to estimate the limit height of the chimney effect when the fire source is 10 m to 200 m from the centerline of the shaft;When the fire source power is 5MW, =-32.46 ln()+ 313.15 can be used to estimate the chimney effect limit height when the fire source is 10-200 m away from the shaft centerline.(3)When the shaft cross-section is square and other conditions(fire source power,ventilation method,shaft section size and shaft inner wall material)remain unchanged,the flue gas movement speed in the shaft decreases continuously along the shaft height direction.