Study on characteristics of fire smoke transportation under smoke exhaust strategy of bifurcated tunnels

Taking a bifurcated tunnel as an example,a simulation study is carried out on the temperature field and smoke spread law in the tunnel under different ventilation schemes during a fire,and the impacts of the wind pressure in the ramp,the wind pressure in the exit section of the main tunnel,and the wind pressure in the widened section of the main tunnel on the smoke transportation characteristics of the fire are analysed.The ventilation scheme of increasing the wind pressure in the ramp and the exit section of the main tunnel is adopted in condition 1 and condition 2,respectively.Comparing the temperature field changes under the two conditions,it is found that the ventilation effect in the exit section of the main tunnel is better than that in the ramp.Condition 3 adopts a ventilation scheme to increase the wind pressure in the widened section of the main tunnel.As the wind pressure in the widened section of the main tunnel increases,the high temperature area above 60 ℃ in the main tunnel continues to shrink,and the temperature within the height of 2 m in the exit section of the main tunnel and the ramp gradually decreases.The increase of the wind pressure in the widened section of the main tunnel is beneficial to tunnel smoke exhaust,but it is not significant.Condition 4 adopts the ventilation scheme of increasing the wind pressure in the ramp.The temperature within the height of 2 m in the main tunnel decreases,and the temperature within the height of 2 m in the ramp increases.If the wind pressure in the ramp is increased,the smoke exhaust effect of the ramp is obvious.Due to the small cross-section of the ramp,it can be considered as a smoke exhaust channel.