Study On Calculation Model Of Tunnel Fire Combustion Characteristics And Smoke Flow Resistance Based On Train Car Ignition Under Low Pressure Environment

With the continuous development of our economy and the continuous deepening of western development,the mileage and quantity of railway tunnel are also rising,which brings convenience while there are more hidden dangers of security.Railway tunnel operation safety problems,the fire caused the greatest harm,because the tunnel space is small,the train on the flammable material,the fire will continue to ignite the goods in the carriage,resulting in the fire development,the temperature rises rapidly in a short time,and produce a large number of toxic smoke,causing serious harm.The distribution of tunnel fire temperature field and smoke field under low pressure environment is obviously different from that under normal pressure environment.Therefore,it is of great significance for disaster prevention and mitigation design of tunnel engineering in low pressure environment to find out the distribution law of temperature field and flue gas field when cross-burning occurs in tunnel carriage.In this paper,through literature investigation,FDS numerical simulation,theoretical derivation,field test and other research methods,the combustion performance parameters of different articles and components in the carriage were summarized in detail,and the fire combustion model of articles in the carriage was established,and the distribution law of temperature field and smoke field in the carriage and tunnel under different fire source location and pressure environment was analyzed.And the smoke flow resistance model under low pressure environment is modified.The main research work is as follows:(1)Through a large number of literature research,the composition and combustion performance parameters of combustibles in each part of the carriage were defined,and12 groups of three-dimensional simulation models of combustibles in the carriage were established under different air pressure conditions(air pressure environment at altitude of 0,3000,4000 and 5000m)and different fire source positions(left side,middle side and right side of the carriage).Combined with the tunnel fire model test data,the reliability of FDS fire dynamic numerical simulation results is verified.(2)Using FDS numerical simulation technology,a large number of calculations have been made to obtain the characteristics and laws of serial combustion of combustible materials in the carriage under low pressure environment.The influence law of air pressure on the heat release rate of fire in the carriage in the process of serial combustion has been clarified,and the characteristics of fire temperature distribution and smoke movement in the carriage have been revealed.At the same time,the temporal and spatial distribution of temperature field and visibility in the tunnel under crossburning condition is studied.(3)The causes and influencing factors of smoke flow resistance were analyzed based on relevant theories such as fluid mechanics and thermodynamics.The pressure variable was introduced to modify the calculation model of smoke flow resistance in tunnel fire,and the reliability of the modified model was verified to make it suitable for calculation and study of smoke flow resistance in tunnel fire under different pressure environments.