Basic Research On Two Zones Method For Gas Flow State In Goaf Based On LBM

Accurately describing the gas flow state and multi-component gas migration state in goaf is a prerequisite for studying the natural combustion and gas distribution in goaf.In the past,porous media fluid dynamics was used to study the gas flow state in goaf,but theoretical research and on-site measurements have shown that the porous media seepage model is only applicable to deep goaf.After the coal seam is mined,within the falling distance of the main roof failure behind the coal working face,the immediate roof collapses under the action of mine pressure.A large number of gaps and large cavities of different scales are generated between the not collapsed main roof and the immediate roof,forming a multi-scale complex medium with overlapping and nested distribution of gaps between rock blocks,gaps between floating coal fragments,large cavities and residual coal body pores.This area is called the new born goaf of coal mines.The gas flow state in goaf behind the working face does not comply with linear or nonlinear seepage laws.The gas flow inside the new born goaf is a natural flow under large-scale space and complex boundary conditions.It is inaccurate to describe the gas flow state of the entire goaf using porous media seepage.In order to more accurately describe the gas flow state in the goaf,a two zones method for the gas flow state in the goaf is proposed.Based on the gas flow state and solid structure in the goaf,the goaf is geometrically divided into two parts for research,one is the new born goaf,and the other is the deep goaf.For the new born goaf,a new born goaf cavity flow algorithm is proposed.Using genetic algorithm（GA）to randomly generate a binary matrix of goaf caving morphology,the error between the gas flow state simulated by lattice Boltzmann method（LBM）and the actual measured data at the boundary or internal measurement points of the goaf is used as the GA fitness value.Quickly approaching the true caving morphology and gas flow state of the goaf through GA.In order to verify the feasibility of the cavity flow algorithm,an experimental model of the new born goaf was constructed,and the velocity of the observation points of the experimental model was tested using a laser Doppler velocimeter（LDA）.The cavity flow algorithm was used to reconstruct the falling morphology and gas flow state of the experimental model.The results showed that the Jaccard similarity between the reconstructed goaf caving morphology and the experimental model caving morphology reached 0.7473.The mean square error between the reconstructed goaf flow field wind speed value and the LDA measured value was 0.0244,and the R² reached 0.8986.The collapse morphology and gas flow state obtained by the cavity flow algorithm are basically consistent with the actual situation.The LBM dual distribution convective diffusion model was constructed to characterize the flow of porous media and the migration state of multi-component gases in deep goafs at the REV scale.The effectiveness and accuracy of the model were verified by conducting SF₆ gas migration experiments in the U-shaped goaf and Fluent numerical simulation.The results show that the absolute error between the LBM simulation results and the experimental results is less than61.2ppm,and the Pearson correlation coefficient（PCC）and cosine similarity are more than 0.8under the conditions of different inlet tunnel wind speed,gas release amount and gas release position.The absolute error between the Fluent simulation results and the experimental results is lower than 109.5ppm,the similarity between PCC and cosine is also more than 0.8.The LBM and Fluent simulation results are basically consistent with the experimental results.However,LBM can achieve automatic modeling and grid partitioning through a 0/1 binary matrix,which is more suitable for the iterative requirements of the cavity flow algorithm.Compared to Fluent,LBM can save up to 25%of the computational time.This research demonstrates the feasibility of the two zones method for predicting the gas flow state in goaf at both theoretical and experimental levels,and has certain guiding significance for achieving the prediction of goaf caving morphology and gas flow state.The dissertation has 69 figures,15 tables,and 124 references.