| The air leakage flow field in goaf is a multi field coupling flow field which is affected by mixed gases' the seepage field,concentration field and temperature field.The study and establishment of goaf multi field coupling calculation model is not only conducive to in-depth understanding of goaf gas flow,but also can reveal the influence of the change of flow state under the fluid in the heat transfer and mass transfer.It has a great theoretical significance for the study of the determination of spontaneous combustion point and the law of gas migration in goaf.Therefore,the purpose of this paper is to set up a three-dimensional dynamic numerical solution model of multi field coupling based on flow tube:(1)The model of mined-out mediaBased on the existing models of capillary model,gap model,hydraulic equivalent model and resistance model,this paper combines the distribution law of porosity of porous media in goaf and the distribution and solid deformation of solid frame,and a porous media model of goaf based on flow tube is proposed.Then,according to the theory of fluid mechanics,the physical characteristics and conservation laws of the flow tube branches in the flow tube model are analyzed in detail,which lays the theoretical foundation for the following research.(2)The distribution of porosity in goafBased on the theory of "key layer" and "thin plate" theory of overlying strata collapse in goaf,the overburden strata of goaf of different assemblage rock series are classified,and the breaking rules and collapse characteristics of different roof are studied.Through the theoretical analysis and numerical simulation,the three types of overlying strata migration and strata behavior of the lower soft rock stratification,the missing of sub-critical layer and the complete roof rock formation is analyzed and studied.Based on the theoretical analysis and numerical simulation results,the zoning characteristics of goaf are analyzed by combining the collapse step,the amount of subsidence and the amount of swing angle.The influence factors and distribution regularity of porosity are described qualitatively.Under certain assumptions,the relationship between the porosity and the subsidence of overlying strata is deduced.Finally,according to the results of numerical simulation,the attenuation law of overlying strata subsidence along the strike direction is fitted.Furthermore,the distribution of porosity in the irregular caving zone in goaf is derived,and the distribution characteristics of the equivalent diameter of the porous medium model is provided.(3)Spatial distribution of gas source in goafThrough measurement of the overall strength of goaf gas phase,and the attenuation law according to gas free desorption,and study the variation of gas emission intensity of goaf in continuous space,a numerical model of multi field coupling numerical simulation of flow field based on flow tube is established.(4)The thermal resistance and and the throttling effectBased on the theory of thermodynamics and fluid mechanics,the viscous obstruction and throttling effect on the flow of the well of the fire are analyzed in depth.On the basis of this,the resistance of fire area is classified according to the different mechanism of the generation of resistance.Then the formula for calculating the thermal resistance of one-dimensional pipeline is deduced theoretically,and the throttling effect of the horizontal pipe is numerically simulated.Numerical simulations show that once the roadway is fired,the viscous resistance in the process of wind flow will increase,and it will increase with the increase of fire scale.The throttle effect is affected by the fire scale and the wind speed in entrance of the roadway,which is enhanced with the development of the fire and weakened with the increase of the inlet wind speed.(5)Multi-field coupling rule based on flow tubeFirstly,the three-dimensional model based on the flow tube is studied in detail.Based on the law of conservation of energy and the law of conservation of mass,the energy balance equation based on the flow pipe loop and the airflow balance equation based on the node of flow tube are deduced and the solution of the basic flow field is realized.Secondly,the diffusion law of single gas source in the basic flow field is studied,and the coupling law of non-single multi-gas source propagation is studied.Finally,the dynamic propagation law of multi-gas source phase is obtained through theoretical analysis.Based on the calculation model of flow tube and the effect of heat on gas flow,the propagation law of heat and its influence on the whole flow field are studied.Combined with the distribution of porous media in the goaf and the distribution law of the gas source,a three-dimensional dynamic numerical model for multi field coupling of goaf based on flow tube is established. |
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