Numerical Research On Gas Leakage And Explosion In Underground Utility Tunnel

“Guiding opinions on promoting the construction of urban underground utility tunnel” issued in August 2015,emphasis that our country strive to build a number of underground utility tunnel with international advanced standards in 2020,which indicates that China’s underground utility tunnel construction will enter a new high tide period.At present,the technical research on safety precautions in underground utility tunnel is still not mature,and the corresponding norms and regulations are not perfect.At the same time,in view of the harmfulness and destructiveness of gas leaks and explosion accidents in gas pipelines,it is necessary to carry out research on gas leakage and explosion in underground utility tunnel,which provides theoretical basis for the revision of the specification and the safe operation.Based on the requirements of the specification for the independent cabin of the underground utility tunnel,the Fluent software is used to simulate and analyze the problems related to gas leakage and diffusion in the underground utility tunnel,and study the effects of leakage aperture,ventilation condition and leakage rate on gas diffusion in the cabin;After the sex and feasibility,the fluent software is used to simulate and analyze the problems related to the gas explosion in the integrated pipe corridor.At the same time,after verifying the accuracy and feasibility of the model,Fluent software is used to simulate and analyze the problems related to gas explosion in underground utility tunnel.The results show that,when the gas leaks,there will be concentration stratification in underground utility tunnel;when ventilation is absent,the cabin gas is symmetrically distributed,and the gas diffusion distance is positively correlated with time in most intervals;when ventilation is present,affected by the movement of eddy currents in the air,diffusion becomes asymmetrical,the gas mass fraction at the ventilation side of the compartment is almost zero,the other side tends to a fixed value,the mass fraction of methane and the leakage time satisfy Boltzmann function.At the same time,the distance and concentration of gas leak will increase with the increase of leak aperture and leak speed.At the same time,when the wind speed is too low,the right side of the leak point will not be thinning,the better dilution effect will be with the higher the wind speed;the time required for the gas concentration from the alarm concentration to the lower explosion limit concentration and the lower explosion limit concentration to reach the upper explosive limit concentration is extremely short.In the same time,the leakage aperture and the speed are larger,and the dangerous area in the gas cabin is larger.The research on gas explosion law shows that there is obvious coupling between explosion overpressure,flame propagation velocity and flame front shape.The explosion process can be divided into three stages according to different forms of flame front.After the premixed gas is ignited,a tiny spherical flame will be formed first,the burning velocity of the flame front is small in the early stage and propagates in the form of a laminar flame.In the later stage,the flame front shape will appear obvious "conical" shape under the turbulence,then gradually transition to the "column" shape and present a "tulip" shape flame,after which the flame burning speed will gradually decrease in the shock until it is zero.There are two peaks in the gas explosion shock wave,and there is a certain periodicity between the two,with a period of 67 ms in numerical simulation.The overall trend of the explosion overpressure is to first decrease slightly and then increase,and the difference between the time when the two overpressure peaks reach the detection position is almost constant,which is 55.8 ms in numerical simulation.The blast wave showed a good linear relationship during the early propagation process.At the same time,the time required for the flame front to reach the detection position and the strongest moment of the flame increased with the increase of the detection distance,and a good linear relationship existed in the early stage.