Study On Gas Migration Law And Numerical Simulation In Goaf Of Fully Mechanized Caving Face

The gas emission from the goaf is the influencing factor that causes the gas concentration in the upper corner to exceed the limit.Studying the law of gas migration in the goaf can provide theoretical guidance for the prevention and control of gas accidents,and optimize and improve the gas drainage in the goaf technology and to improve production safety.Through the study of the collapse mechanism of the overlying rock strata in the goaf,the distribution formula of the breaking expansion coefficient at the floor plane in the goaf is established,and then the spatial distribution equation of the porosity in the goaf is obtained.By using UDF to compile the empirical formulas of porosity,viscous resistance,inertial resistance parameters and spatial position in porous media,a goaf model in which porosity changes continuously with spatial position is realized.Through FLUENT numerical simulation,the influence of the distribution of the porosity in the goaf and the flow pattern of gas on the gas migration law was discussed,and the gas concentration in the goaf under the conditions of U-shaped ventilation and high drainage roadway conditions was compared and analyzed.The results show that the setting of the porosity of the goaf and the setting of the gas flow pattern have an important influence on the gas migration in the goaf.Under the condition of non-linear flow of gas in the goaf,when a fixed constant is used to set the porosity coefficient in the goaf,the air leakage area in the goaf is distributed in a rectangular shape.When the goaf uses variables instead of fixed parameters to set the porosity coefficient,the air leakage area of the goaf is a right triangle with a large area near the lower corner and a small area near the upper corner,and the gas concentration in the upper corner of the goaf under the constant porosity distribution state is smaller than the gas concentration in the upper corner of the goaf under the variable porosity distribution state;When the gas seepage method in the goaf adopts linear seepage,there are air leakage vortices at the upper and lower corners of the goaf,and the gas concentration is low,the gas concentration near the support is high,showing irregular symmetry,and the gas concentration in the upper corner of the linear flow method is smaller than that of the nonlinear flow method.Combined with the actual situation of 402102 working face,make reasonable simplifying assumptions,study the law of gas migration in the goaf under high drainage roadway conditions,the ratio between the flow of the high drainage roadway tunnel and the flow of the return air tunnel is used as the drainage weight,the simulation obtains the upper corner gas concentration,high-drainage roadway gas concentration,and gas scalar under different drainage weights.The results show that increasing the drainage weight of the high-drainage roadway can reduce the gas concentration in the upper corner and increase the gas drainage of the high-drainage roadway,but at the same time it also leads to a decrease in the drainage concentration.