Three-dimensional Numerical Simulation Of The Natural Gas Leaked Diffusion Under The Complex Surface Configuration

During the natural gas gathering and transportation, the accidents of natural gas leakage and explosion were frequent at home and abroad , because of unsealing between piping fittings, corrosion perforation, mismanagement etc.. So simulating the diffusion process of gas pipeline leakage, and predicting the spread of natural gas ,can reduce the human and economic losses greatly ,which caused by diffusion, fire, explosion. As a result, there were great significance and scientific value to prevent and control of such incidents, to ensure the safe operation of pipelines, to protect the safety of humans and properties. However, the surface configuration the pipelines passed was complex and diverse, such as, plains, mountains, villages and cities. So, dealing with the nature gas leaked diffusion under the complex surface configuration, was a pressing need.By way of summarizing the characteristics of natural gas, and the factors that affected the diffusion process, and the risks of long-distance gas pipelines, according to the theories of fluid dynamics and thermodynamics, I analyzed the leakage of natural gas pipelines and turbulent jet theory, proved that the bore diameter of leaking can't be determined according to the pressure drop rate only, and established a method of calculating the bore diameter of leaking and leakage in any time with the help of SCADA system.Based on analyzing the most influential factors that affected natural gas diffusion - wind characteristics, and according to the theories of wind velocity dissipation and construction mechanics, I know that the barriers on the wind direction had a significant impact on the profile of wind in height gradient, different height gradient profile curves were reflected in the different wind speed index, or different roughness in this location. They could express briefly as: wind speed affected gas diffusion, surface roughness (wind speed index) affected the wind speed and height gradient, the terrain obstacles determined the surface roughness. Finally, with the help of GIS, I based on the distance of construction barriers from the location of leakage, size, height, sparse degree and direction, to converse the ground roughness of this location by some formulas, thus, established a quantitative approach to distinguish different surface configuration in GIS, and simulated pertinently. Ultimately I solved the problem of three-dimensional numerical simulation of the nature gas leaked diffusion under the complex surface configuration.Finally, based on the above model, I used the computational fluid dynamics simulation software FLUENT to simulate, and summarized the situations of gas diffusion in different external wind speeds, different pipeline setup modes, different injection angle, different leak aperture, different terrain, different pressure; I also get the conclusion about time of the gas clouds stable on the non-steady state , that the smaller were boundary concentration of natural gas, the longer time was they need.