Study On The Effect Of Train Obstruction And Tunnel Slope On Smoke Characteristics For Subway Tunnel Fire

While the metro brings convenience to people,it also poses a great challenge to fire safety.The blocking effect of metro train and tunnel slope will affect the tunnel fire smoke flow,increasing the difficulty and complexity of tunnel fire smoke control.The metro train affects the distribution of the air flow field in the tunnel,so that the longitudinal velocity in the tunnel blocked zone increases,forming an obvious vortex behind the metro train,which in turn affects the smoke flow,temperature distribution and fire plume flow changes in the tunnel.The tunnel slope causes natural wind pressure inside the subway tunnel,and the natural wind pressure also causes changes of smoke,temperature and fire plume flow inside the subway tunnel.Therefore,it is of great practical significance and good engineering application value to study the influence of blocking effect of metro train and tunnel slope on smoke flow characteristics of subway tunnel fire.In this paper,the research methods of literature research,theoretical analysis and numerical simulation are used to analyze in depth the influence of blocking effect of metro train and tunnel slope on the smoke flow characteristics of subway tunnel fires.The specific work and research results are as follows:(1)Under natural ventilation conditions,the effect of tunnel slope on the smoke flow characteristics of tunnel fires was studied.It was found that the temperature at the fire source in the tunnel was the highest,and the temperature in the tunnel gradually decreased with the increase of the longitudinal distance from the fire source,and the difference of the temperature drop rate between the two sides of the fire source gradually increased with the increase of the slope;the back-layering length of the uphill tunnel fire gradually decreased with the increase of the slope,and the smoke in the downhill tunnel gradually decreased toward the spreading distance of smoke to the downstream side of the fire source gradually becomes smaller.(2)Using the validated numerical model of subway tunnel to study the effect of tunnel blockage ratio on the back-layering length and critical velocity,it is found that the back-layering length gradually decreases with the increase of blockage ratio and longitudinal velocity,and the correction factor of the critical velocity reduction ratio and the metro train blockage ratio is found to be 0.545;The critical velocity in the unblocked zone of a metro train is higher than that without a subway train blockage.With an increase in the blockage fire source distance,the critical velocity first decreases and then tends to be constant.(3)Under longitudinal ventilation conditions,the effects of tunnel slope and blockage and their combined effects on the critical velocity of tunnel fires were investigated.It is found that the critical velocity value gradually decreases in the uphill tunnel and increases in the downhill tunnel.Compared to the critical velocity for horizontal subway tunnel,the critical velocity increases for downhill tunnel and decreases for uphill subway tunnel.In the same slope tunnel fire,the larger the tunnel blockage ratio is,the smaller the required critical velocity is.By analyzing the changes of the critical velocity of subway tunnel fires under the combined effects of subway train blockage effect and tunnel slope,a subway tunnel fire critical velocity prediction model considering subway train blockage effect and tunnel slope is established.The research results of this paper can provide theoretical basis and research experience for the engineering design of subway tunnel fire smoke control and ventilation and smoke exhaust system.