Research On Numerical Simulation Of Gas Diffusion Resulted From Leakage Within Urban Buildings

It will be a great threat to safety of life and property of people when fire and explosion accidents that caused by gas diffusion happens.At present,gas diffusion within large scale urban buildings is not been enough researched.The research status and methods of gas leakage and diffusion in domestic and abroad are analyzed and studied,mathematical models of the leakage rate on different leakage holes of gas pipeline are derived by using the relative theories of fluid mechanics and engineering thermodynamics,and then the leakage rate calculation procedures are programmed.The gas diffusion coefficients are calculated by adopting Chapman-Enskog theoretic equation.The wind field around building and the concentration field of CH4 gas diffusion are simulated in the FLUENT software,the calculation accuracy and efficiency are improved by optimizing the quality of grid with technologies of partion meshing,Interface and adaptive mesh refinement,the boundary flow parameters are controlled by User Defined Function(UDF)procedures.The comparison between average pressure coefficients calculation results and field data shows that average relative errors are 25.8%.The comparison between concentration of gas calculation results and experimental data shows that average relative errors are below 14.5%.these results demonstrate that the relevant numerical simulation theories and methods used in predicting gas diffusion are reasonable.Influencing factors of gas diffusion are discussed and analyzed,the results indicate that the effects of leakage rate,leakage source location,wind speed,atmospheric stability and distribution of building height are more obvious,then followed is the different distance between buildings,the effects of humidity and temperature are nearly negligible.Pressure field,wind field and concentration field of gas diffusion at streets and intersection of urban buildings are simulated,the effects of pressure field and wind field on gas diffusion are analyzed,and the law of gas diffusion is obtained.The research results can provide scientific references to operating safely and security of urban gas.