Study On Smoke Propagation Characteristics And Smoke Exhaust Effect Under Natural Ventilation Shaft Mode In A Tunnel Fire

In order to alleviate the increasing traffic pressure,more and more tunnels are put into operation.The tunnel is a long-narrow structure,in the event of a fire,it is easy to cause casualties.In recent years,more and more tunnels have gradually adopted the natural ventilation mode with vertical shafts,however,in the previous studies,mechanical smoke was more concerned,and there are few studies on natural ventilation mode.Therefore,based on this situation,the following research contents are established:The effects of the transverse distance from fire source to tunnel sidewall,the longitudinal distance from fire source to shaft and the transverse distance from shaft to sidewall on natural ventilation effectiveness in a tunnel fire were studied.The typical characteristic parameters of smoke,such as mass flow rate,temperature distribution and velocity vector were analyzed,besides,the phenomenon of plug-holing was mainly discussed.The results have shown that the mass flow rate of gas exhausted by the shaft decreases slightly with the increase of longitudinal distance from fire source to shaft.When the longitudinal distance from fire source to shaft is constant,changing the transverse distance from shaft to sidewall will have a more obvious effect on the effectiveness of exhausting smoke than changing the transverse distance from fire source to tunnel sidewall,the phenomenon of plug-holing is more serious when the shaft is close to the sidewall.The effects of the fire source at different locations between the two shafts on the natural ventilation effectiveness in a tunnel fire was studied.The temperature distribution in the tunnel,the mass flow rate and the CO concentration of smoke exhausted from the shaft were analyzed,besides,the special phenomena of plug-holing and smoke bifurcation were also discussed.The results showed that the occurrence of longitudinal wind inhibits the phenomenon of plug-holing.The fire location has little effect on the maximum smoke temperature under the ceiling,the maximum temperature rises of smoke under the ceiling decreases exponentially with the increase of longitudinal wind.The effects of the heat release rate and fire-fire distance on natural ventilation effectiveness and temperature distribution in a tunnel under multi-source fires were studied.The results showed that when there is a certain distance between the fire sources,the two flames are inclined and close to each other.When one of the fires is located downstream of the shaft,the mass flow rate of smoke exhausted by the shaft is relatively high.As the distance between the fire sources continues to increase,the mass flow rate remains substantially stable.The relationship between thee mass flow rate and fire location is established.