| At present,the research on the leakage of underground gas pipeline mainly focuses on the leakage and diffusion law of underground soil space,and rarely focuses on the study of gas leakage in the whole process of soil atmosphere,and mainly focuses on two-dimensional simulation.This paper will study the leakage and diffusion law of gas in soil under different leakage conditions by three-dimensional numerical simulation.Whether gas can gather in the atmosphere space and the change of hazardous area caused by gas leakage from soil to atmosphere,which provides theoretical basis for preventing gas leakage accidents and maintenance work after leakage.In this paper,the three-dimensional numerical simulation of the leakage and diffusion of underground gas pipelines in cities and towns is carried out.The control equation of fluid flow is solved by theoretical analysis,and the theoretical formula of pore leakage strength is obtained,which is used as the basic formula for fitting the data of the subsequent semi empirical formula.The geometric and mathematical models of each problem are established and the control equations are solved by the finite volume method.The leakage and diffusion law of buried gas pipeline in soil was studied.The results show that when the soil porosity is constant,the larger the porosity is,the faster the gas diffusion speed is;When the soil porosity changes with the depth,the deeper the buried depth of the pipeline,the smaller the pipe diameter,the greater the resistance of the gas,and the slower the gas diffusion speed.The larger the aperture is,the faster the gas diffusion is.When the leakage hole is located at the top of the pipeline,the gas diffusion speed is faster,the side wall leakage takes the second place,and the bottom leakage time is the slowest.The smaller the distance between the two leakage holes is,the faster the gas diffusion is.The shape of leakage hole has little effect on gas leakage.Pipeline pressure has a great influence on the leakage of buried gas pipeline.The larger the pipeline pressure is,the faster the gas leakage diffusion speed is.When the soil porosity is constant,the influence of pipe diameter and buried depth on gas leakage and diffusion is very small.The diffusion law of gas leakage in atmospheric space is studied.The conclusion is as follows:the higher the height of the building,the easier the gas accumulation in the cavity of the building group.The larger the distance between buildings,the more difficult it is for the gas to accumulate.The location of the leakage hole has little influence on the gas diffusion in the atmospheric space.For the influence of external wind speed,when there is no external wind speed,the gas will spread vertically upward,and it is not easy to accumulate in the cavity of the building group.At low wind speed,the gas will gather in the leeward side of the building upstream of the leakage hole.With the increase of wind speed,the turbulence effect will continue to increase,and the gas will quickly dissipate into the atmospheric space.The diffusion law of the building and soil porosity on the gas in the soil atmosphere coupling space is studied.The conclusions are as follows:when there is no building on the surface,the gas will spread vertically upward;when there is a single building on the surface,the gas will spread to the building side first and then spread upward along the building wall;when there are two buildings on the surface,the gas will be affected by many buildings,and the diffusion is limited near the surface.The dangerous area of gas under the condition of no building and single building is not much different.The dangerous area without building condition appears later and the expansion speed is slower.The smaller the porosity of soil,the smaller the range of dangerous area of gas in the atmosphere space,the earlier the dangerous area appears.When the soil porosity is less than the critical value,the dangerous area will appear earlier,and the scope will be larger.Figure[63]Table[7]Reference[83]. |
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