Abstract
The characteristics of a pulverized coal jet flame ignited by a preheated gas flow are modeled with large eddy simulation (LES) method. An open-source computational fluid dynamics (CFD) code –OpenFOAM (open field operation and manipulation) is applied to predict the instantaneous temperature, pressure, vortices and species mass fraction of the whole combustion process. The sub-grid scale (SGS) turbulence and combustion models based on the one-equation eddy-viscosity model and the kinetic-diffusion limited rate surface reaction model are used in the modeling process. Jet combustions with different inlet velocities are simulated to get an optimal value under the condition that a good combustion kinetic filed can be established. In order to prove the advantages of LES on the predictions of turbulent combustion, Reynolds-averaged Navier-Stokes (RANS) simulation has been performed and compared with the results of LES. The results suggest that LES can predict the instantaneous values of turbulent combustion while RANS can only get average effects. The ability of LES to capture the high and low values of temperature and species concentrations is better, and it can capture the flame centre and predict the recirculation flows more accurately than RANS. Furthermore, the effect of coal particle diameters on the flame characteristics is also investigated by LES. It has been observed that the region of high temperature is wider, the flame center is closer to the nozzle exit, and the local temperature is higher for smaller particles. The results also show that the combustion is more intensive and complete for smaller particles, which are coincident with the combustion theory.
Utilization of high order DRP-type schemes and large eddy simulation based on relaxation filtering for turbulent gas flow computations in the case of Taylor-Green vortex breakdown