OpenFOAM applied to the CFD simulation of turbulent buoyant atmospheric flows and pollutant dispersion inside large open pit mines under intense insolation

Abstract

The particular conditions of air circulation inside large open pit mines under intense insolation, dominated by mechanical and buoyant effects, are crucial when studying the dispersion of pollutants inside and outside the pit. Considering this, we study this problem using CFD tools able to include the complex geometry characterizing it and the different processes affecting circulation: flow interaction with obstacles, buoyancy, stratification and turbulence. We performed simulations using a previously developed OpenFOAM solver, focusing in the particular case of Chuquicamata, a large open pit mine ( 1 km deep) located in northern Chile. Both idealized and real topographies were used. Given the importance of turbulence in this type of large-scale flows we have used LES to incorporate it in the calculation, using a DES approach to solve the flow near walls. The results from the idealized cases support the idea that buoyant currents foster the exit of particles from the pit and increase the turbulence inside its atmosphere, modifying the purely mechanical recirculatory flow inside the cavity. Differences in the air circulation and dispersion of particles between idealized and non-idealized cases are reported. In particular, there are changes in the intensity and location of the recirculation inside the pit due to variations in the aspect ratio (length/depth) of the cavity along the axis perpendicular to the main flow. Also, the topography surrounding the mine affects the main flow that sweeps the cavity, channeling it along the main axis of the pit and forcing it to enter the cavity through the lower level of the top edge. As a consequence, the patterns of pollutant transport observed in the idealized cases, dominated by near-wall upward currents, are different than those observed in the cases with complex topography, where the dispersion is dominated by internal buoyant upward currents. Anyhow, whether by internal or near wall upward currents, in all buoyant cases considered a large percentage of the particles injected inside the pit leaves the cavity. Further experiments studying the effect of 3D aspect ratio over the mechanically forced internal flow are needed to fully understand the effect of the internal geometry of the pit over the flow.