Simulation of gas migration in 3D goaf based on RNG k-Ε turbulence model

For the study of gas floating characteristics and distribution in 3D goaf, according to mass conservation, conservation of momentum, and Fick's law, suitable for fully mechanized goaf, describing the variable density of the air-gas mixture, nonlinear flow-diffusion equations were built. Combined N2-706 coal face in Daxing Mine, using CFD software, the author simulated the transport and distribution of gas in 3D goaf. Heterogeneity of caving in flow field was described as the O type. RNG k-Ε turbulence model was used, and taking into account the gravity field conditions. The results of theoretical calculations were consistent with the actual conditions and gas monitoring data. Authors point out that gas floating characteristics and distribution in 3D goaf, is due to the air flow moves, gas diffusion-dispersion, and the floating migration of gas-flow which caused by its density difference, and it is also a dynamic balance, which depends on constant desorption of gas in flow field and continuous inflow of air leakage. The results show that the flux of extracting gas from high drill holes is approximately inversely proportional to the volume percent concentration of extracting gas, and has a negative exponential relationship with volume percent concentration of gas in return air tunnel.