Estimation of aeration time in blind excavations: methodological approach based on 3D numerical modeling

The paper presents the results on 3D numerical modeling of ventilation in blind excavations of different length under the fixed transverse section due to turbulent diffusion. Aerodynamic characteristics have been calculated using the standard ( k - ε)-model of turbulence. The ventilation in an excavation has been simulated by numerical solution of a convectional-diffusion equation of admixture transfer. Numerical experiments of ventilation a blind excavation with 10 - 20 m length have been performed for range of air consumption in a through excavation from 6.25 to 50 m3/sec. Initial contamination of the atmosphere in the blind excavation has been taken in the range of 15 - 25 MPC (in nitric oxides). For boundary conditions observed there have been received spatial distributions of the velocity field and coefficients of turbulent viscosity in the excavation's length. The authors have revealed significant heterogeneity of the velocity field in the blind excavation and low values of velocity vector's components close to a face; this leads the turbulent diffusion mechanism to a prevailing position in the admixture dispersion. The paper presents examples of admixture distribution in excavations' space at the moment of the MPC level achievement in the blind excavation depending on the values of the model's varying parameters. It has been established that the ventilation time under otherwise equal conditions depends significantly on amount of air supplied to the main excavation. It has been shown that at initial and boundary conditions adopted the forecast of ventilation time for blind excavations through the turbulent diffusion mechanism can be performed based on integrated analytic correlation with such arguments as excavation length, air consumption and initial level of gas contamination. The analysis of numerical test results performed on the basis of 3D models designed has shown that the blind excavations with length more 10 m where stoping operations are running can be ventilated due to the turbulent diffusion mechanism. Time of the blind excavation ventilation in dependence of gases concentration in it can reach more than two hours in dependence of volume of air supplied in a through excavation.