Influencing Factor Analysis Of Smoke Flow In Subway Tunnel Fire

As a powerful tool of urban rail transit,the subway has become the main means to solve the problem of urban traffic congestion.The safety of passengers severely affected by subway fire smoke.The ventilation and smoke exhaust system of subway tunnels is an important technical measure to control the flow of smoke in subway tunnel fires.If the longitudinal wind speed of the tunnel is greater than the critical wind speed of the subway tunnel fire,there will be no smoke backflow phenomenon,which improves the favorable conditions for the safe evacuation of passengers and fire fighting.It is an important design basis for the subway ventilation and smoke exhaust system when the back-layering length and the critical velocity of the subway tunnel.Therefore,studying the influencing factors of the fire smoke flow law of subway access line tunnels has important theoretical significance and engineering applications.This paper comprehensively adopts theoretical analysis and numerical simulation research methods to carry out analysis and research on the factors affecting the law of smoke flow in subway tunnel fires.Through non-dimensional analysis,the main influencing factors of the fire smoke flow law in subway tunnels are clarified.From the perspective of guiding the engineering design of the ventilation and smoke prevention and exhaust system of subway access lines,the outdoor air parameters,tunnel slope,V-shaped slope,and tunnel height are studied.And the influence of the fire source heat release rate on the fire smoke flow law of subway access line tunnels,the research results can be used to guide the value of the design parameters of subway access line tunnel ventilation,smoke prevention and exhaust.The results of the study show that the higher the outdoor air temperature,the shorter the back-layering length in the subway tunnel;the lower the outdoor air temperature,the longer the back-layering length in the subway tunnel.The outdoor air temperature in winter should be used to study the back-layering length in subway tunnels and the critical velocity.The greater the outdoor atmospheric pressure,the shorter the back-layering length;the lower the outdoor atmospheric pressure,the longer the back-layering length.The critical velocity of tunnel fire should be determined according to the local outdoor atmospheric pressure of the metro city.The greater the outdoor air humidity,the shorter the back-layering length in the subway tunnel;the lower the outdoor air humidity,the longer the back-layering length in the subway tunnel.The smaller outdoor air humidity should be used to determine the back-layering length of the subway tunnel and the critical velocity of the fire.The critical velocity of the uphill tunnel(with a positive angle)decreases with the increase of the tunnel angle;the fire critical velocity of the downhill tunnel(with a negative angle)increases with the increase of the tunnel angle.When determining the back-layering length and the critical velocity of the V-shaped slope tunnel,the influence of the natural ventilation competition effect of the V-shaped tunnel should be considered.The greater the heat release rate of the fire source,the greater the back-layering length and the critical velocity of the subway access line tunnel.The smaller the heat release rate of the fire source,the smaller the back-layering length and the critical velocity of the subway access line tunnel.As the subway access section tunnel is a non-passenger section tunnel,there are no passengers and luggage in the subway train.Therefore,the two most commonly used typical fire source heat release rates for subway access tunnel fires are 5MW and 7.5MW.The higher the height of the subway tunnel,the smaller the back-layering length and the critical velocity;the lower the height of the subway tunnel,the greater the back-layering length and the critical velocity.