Research On Numerical Simulation Of Airflow Field In Gob Areas Of Long Wall Coal Mining

In the past years, the top-dropping method of fully mechanized coal mining is broadly adopted in the coal industry. As the volume of roof cave-in is huge, the coal left in the gob is in a large quantity and air leakage is significant, the danger of coal spontaneous combustion in gob is realistic and seirous. Furthermore, fully mechanized mining has a high capacity of production, leading to a higher level of gas emission with larger range of fluctuation, and further causing a high level of gas concentration in the return airflow and at the upper-corner of working faces. All of these constitute the potential dangers long being existing in coal mines.The trend of self-ignition of residual coal and methane accumulation in gob is closely related to the air leakage in the gob. The air leakage pattern in gob is difficult to measure or to simulate due to technical limitation and cost, so the computational fluid dynamics is used to simulates the pattern of air leakage flow in the gob.By analyzing the environmental characteristics of a gob, the porosity distribution can be obtained, and a two-dimensional model with one source and one influx is built and meshed by Gambit software. The governing equations of airflow through porous medium are set up and solved by using CFD software of Fluent to simulate the dispersion law of airflow in gob.As the porosity in gob changes from place to place, the simulation is performed in two categories, namely the simulation in case of symmetrical porosity and the simulation in case of unsymmetrical porosity. Based on the gas drainage methods adopted in gob, each category considers three patterns of gas drainage, i.e. through gas drainage holls, arranging gas outflow passage ways and adopting up-roof gas drainage lanes. The simulation is performed in three steps: firstly, simulation under a group of intricate boundary conditions including both airflow and gas drainage; secondly, simulation under boundary conditions of airflow and gas drainage respectively, then taking vector stacking to obtain the dissolute distribution in gob. The simulation provides foundations of the spontaneous combustion prediction and gas accumulation pattern in gob. Through comparison of the results, it can be concluded that the relative error of the two groups of results is insignificant, which indicates that it is feasible to resolve a complicated simulation into a series of simulations with simpler boundary conditions, complete simulation and then compose the results. It also indicates the feasibility to construct a platform to simplify the simulation process.