Research On Optimization Of Ventilation And Smoke Exhaust System In Urban Complex Tunnel

Urban complex tunnels are characterized by long lines,multiple ramps,multiple shafts and large traffic flow.The change of airflow in the tunnel is more complex than that in conventional linear tunnel,and the probability of fire accidents is also larger,which seriously affects the design and management of the tunnel ventilation system.Therefore,it is necessary to carry out a study on the optimization of the ventilation and smoke exhaust system in urban complex tunnels.The main research and conclusions are as follows:(1)SES numerical simulation method was used to study the ventilation system of an urban complex tunnel under different traffic conditions,and a reasonable ventilation equipment configuration scheme was proposed to optimize the tunnel operation ventilation system.The results show that the piston wind generated by vehicle driving can not meet the ventilation requirements of urban complex tunnels,which requires mechanical ventilation;It is suggested that some working shafts should be set as air inlet shafts to supply fresh air to the tunnel.(2)Aiming at the natural ventilation of the shaft group in the shallow buried section,the full-scale numerical simulation was used to studied and analyzed the effects of the shaft groups under different arrangement on the natural ventilation when the total cross-sectional area of the shaft groups is constant.The results show that when the heat release rate of the fire is 20 MW,boundary layer separation occurs in all shafts under various conditions.When the number of shafts N is ≤ 2,the comprehensive smoke exhausting capacity of the shaft groups arranged above the middle of the tunnel is better than which above the side;when N is >2,the shaft groups arranged above the side of the tunnel have a better overall smoke exhaust effect.(3)The FDS numerical simulation method was used to study the coordinated smoke exhaust effect of the jet fan and the side shaft groups.The results show that the results show that the smoke bifurcation phenomenon downstream of the fire source is intensified by the increase of jet velocity,and the total volume of smoke exhausted from the shaftgroups is reduced.When the fire source is 25 m away from the shaft group,the total smoke exhaust effect of the shaft groups is the best.