Research On The Phenomenon Of Plugholing Under Central Extraction System In Tunnel

The tunnel ventilation and smoke extraction system has played an important role in controlling the spread of fire smoke and reducing the damage of high-temperature smoke and flame on the tunnel structure and personnel.In this paper,to study the characteristics of the plug-holing in the central smoke extraction system through the methods of small-scale model experiment,theoretical analysis and numerical simulation are conducted,so as to provide the theoretical support for the design of fan in the exhaust system tunnel.The main research work and results are as follows:(1)To reveal the evolution process of the smoke layer plug-holing in the central smoke extraction tunnel.Studying how the different mechanical smoke exhaust volumes affects the plug-holing by small-scale model experiment,and analyzing the changing rules of the smoke layer temperature,thickness below the smoke vent under different mechanical smoke exhaust volumes,by which the process of the plug-holing is divided into three stages: no plug-holing,transition area,plug-holing;The analysis of the differences between the two critical smoke exhaust rate by the critical Froude number,and result shows that the smoke exhaust rate when the plug-holing occurred in the test is greater than the critical smoke exhaust rate calculated when the critical Froude number by Morgan for 1.5,and the critical Froude numbers obtained when the plug-holing occurred in the central smoke extraction tunnel through the experimental analysis are 1.2 and 1.8.(2)To design the reasonable smoke exhaust volume in the road tunnel with central exhaust system,the influence of the critical smoke exhaust rate on the efficiency of the road tunnel with central exhaust system was studied by constructing the 1:20 scale tunnel model.By measuring the smoke layer temperature,thickness at 5 kinds of heat release rate and different mechanicalsmoke exhaust volumes,and these critical smoke extraction rate test values was got under different heat release rate when the plugholing occurred.Comparing these values of model test with these calculated values by Heselden model and TM19-1995 model and analyzing the differences of three kinds of critical smoke exhaust rate calculation model.To introduce the correction coefficient of heat release rate on the basis of the TM 19-1995 model and got the corrected critical smoke extraction rate calculation model changing with the non-dimensional heat release rate in the central exhaustion road tunnel.(3)To determine the reasonable design scale of longitudinal air supply volume.It’s vital to study the change rule of the distance of smoke spread and the thickness height and the smoke extraction efficiency under different longitudinal air supply volume by the method of numerical simulation,then get the conclution that the longitudinal air supply volume should be designed in the mechanical exhaust volume between 70%~90% based on these three indexes restrict.