Research On Fire Smoke Control And Exhaust Technology Of Large Longitudinal Slope Curve Ramp In Underground Interchange

The underground interchange is a new type of underground highway that realizes the intersection of different types of road lines,the intercommunication of multi-directional lines and effectively relieves the traffic pressure.And the smoke control strategy is different from the simple single tunnel.The large longitudinal slope curved ramp is an unfavorable section for fire smoke control in underground interchanges.Once a fire occurs,if the smoke is allowed to spread unorganized,it will greatly endanger the life and property safety of people.Therefore,whether the fire smoke can be guaranteed to be in a controlled state directly determines the disaster prevention safety of the entire underground interchange project.At present,there are few studies on the fire smoke characteristics and smoke control related to the large longitudinal slope curve ramp of the underground interchange,and it is necessary to conduct in-depth research.Relying on the underground interchange of Hengjiang Avenue Section of Jianning West Road Crossing the River Crossing Project in Nanjing,this thesis combines the methods of literature investigation,theoretical analysis and CFD numerical simulation to research the characteristics of the free spread of fire smoke,the distribution law of the variables of each fire site along the route and the effect of smoke control under different smoke exhaust modes in the large longitudinal slope curve ramps.The main research work and conclusions of the paper are as follows:(1)Establish 3D numerical models of ramps A(i<0)and C(i>0)with large longitudinal slope curves,and research the spatiotemporal distribution of variables under the free smoke spreading and one-way smoke spreading.The smoke fronts under the ceiling reaches the upstream entrance and downstream exit 200s and 210s after the fire,respectively.The maximum length of smoke spread downstream of ramp A is 138m,and the maximum length of smoke spread upstream of ramp C is 82m.By comparing the one-way spread characteristics of flue gas under different longitudinal wind velocity,the critical velocity of ramp A and C are2.9m/s and 2.0m/s under 30MW HRR,3.1m/s and 2.2m/s under 50MW HRR.(2)Establish a 3D numerical model of central smoke exhaust system on the top of ramp A with large longitudinal slope,and the effects of different induced velocity,smoke exhaust vent sizes and fire source positions on the smoke control and exhaust of the ramp were studied.By analyzing the results such as smoke spread range,temperature,CO concentration,visibility,as well as the temperature,flow velocity and smoke exhaust efficiency of smoke exhaust vents,it is concluded that when the length-width ratio of the smoke exhaust vent is 4:1 and the area is6m~2,the smoke control and exhaust effect of the ramp and the evacuation environment for people are better.When the fire source is located in the middle of the ramp,the induced longitudinal wind velocity of 1.5m/s and the smoke exhaust volume of 150m~3/s can achieve better smoke control and exhaust effect.When the fire source is located near the 2#exhaust vent,the induced velocity needs to be increased to 2.0m/s,and the smoke exhaust volume also needs to be increased to 210～240m~3/s in order to prevent the"cross-regional spread"of fire smoke effectively.When the fire source is located near the 5#smoke exhaust vent,the induced velocity is maintained at 1.5m/s,and the smoke exhaust volume is increased to 210m~3/s can meet the smoke control requirements on the ramp.(3)Two 3D numerical models(outside and inside)of central smoke exhaust on the sides of ramp A with large longitudinal slope is established to analyze the influence of different positions of the exhaust flue on the effect of central smoke exhaust mode,and to optimize the parameters of smoke control and exhaust when the exhaust flue is placed inside.By comparing the fire smoke field,temperature field,the distribution law of CO concentration and visibility when the flue is located on the top,outside,and inside of the ramp respectively,it is concluded that the smoke control effect when the exhaust flue is placed on the top of the ramp is much better than that when the exhaust flue is placed on the side of the ramp,and the exhaust flue is placed on the inside better than that when the exhaust flue is placed on the outside.As an example that when the smoke exhaust flue is placed on the inside,and the fire source is located in the middle of the Ramp A,it is recommended that the induced velocity should be 1.5m/s,the exhaust smoke volume should be 210m~3/s,and the internal spacing of the smoke exhaust vent should be 50m.