Study On Characteristics Of Ceiling Jet And Smoke Control Of Wall-Attached Fire Plume In The Tunnel

Recent years,the urban underground space utilization is also constantly expanding,and the number of traffic tunnels and channels is constantly increasing.The safety issues have also attracted widespread attention,among which the fire safety is closely related to them.A lot of researches have been done on the characteristics of fire plumes in narrow and long confined spaces at home and abroad,but there are few studies on the characteristics of ceiling jets and smoke exhaust control induced by wall-attached fire plume in confined spaces of narrow and long tunnels.For wall-attached fire plumes in narrow and long spaces,due to the restriction on the entrainment of the fire plume by the side wall of the tunnel,the characteristics of the fire plume,including plume temperature rise,heat flux,flame shape and smoke control,are different from the fire plume that occurs in an open space.Through theoretical and experimental research,this paper analyzes and reveals the characteristics of the ceiling jets behavior and the law of smoke exhaust control induced by wall-attached fire plumes in the tunnel.The specific research content is as follows:Firstly,the evolution of characteristic parameters of ceiling temperature caused by wall-attached fire plumes inside the tunnel with different rectangular burners are experimentally studied.It is found that,for a certain heat release rate and distance between fire source and tunnel ceiling,the lateral temperature under the ceiling reduced gradually with the increase of the radial distance from the upper edge of the wall,and increases with the increase of the rectangular burner aspect ratios.Then,a new characteristic diameter is defined in this paper,it is used to describe the characteristics of the lateral flame extension length under the tunnel ceiling,and a dimensionless model of the flame expansion under the tunnel ceiling is established.In addition,a characterization model for the lateral temperature rise under the ceiling induced by wall-attached fire plumes in the tunnel is proposed.The main influencing factors including the characteristic diameter of rectangular fire source and non-dimensional heat release rate.Secondly,the evolution of characteristic parameters of ceiling heat flux induced by wall-attached fire plumes inside the tunnel with different rectangular fire source in the paper is studied.The study found that the ceiling jet induced by wall-attached fire plume is significantly different from the previous literature(the square fire source is generally used)when the rectangular fire source is relatively large in length and width.For the square fire source in the tunnel,the total heat flux distribution under the tunnel ceiling increased as the heat release rate of the fire source increased,whereas it decreased as the distance to the tunnel side wall increased.As the source-ceiling height increased,the total heat flux decreased.For wall-attached fire plume with different rectangular fire source,the total heat flux under the tunnel ceiling gradually increased as the fire source aspect ratio increased.The heat flux distribution characterization model under the tunnel ceiling induced by wall-attached fire plume with different rectangular fire source is proposed.The temperature contours under the ceiling were also analyzed and compared with the heat flux distribution field map to verify the findings.Finally,the control of smoke exhaust induced by wall-attached fire plume inside the tunnel is studied.It is found that the smoke characteristics of wall-attached fire plume and free fire are obviously different under different smoke exhaust modes.For the ceiling/lateral concentrated smoke exhaust,the smoke exhaust efficiency of wall-attached fire plume increases with exhaust smoke volume in the tunnel.When the “plug-holing”exhaust smoke volume is reached,the efficiency of smoke extraction will suddenly decrease,and then continue to increase with the increase of exhaust smoke volume.Contrast from the ceiling smoke concentration,lateral concentration exhaust critical Froude number slightly larger,this is due to the lateral exhaust port is set in close to the tunnel side wall,due to the feedback effect of the tunnel side wall,lateral concentrated vertical smoke temperature is higher than ceiling smoke concentration exhaust,and the lateral concentrated part exhaust smoke temperature is higher,resulting in the same conditions,the lateral concentration exhaust efficiency is lower than ceiling exhaust smoke exhaust efficiency,and the Froude number is higher than ceiling.