Calculation of Kiln Aerodynamics with two RANS Turbulence Models and by DDES

Abstract

Rotary kilns are large, cylindrical, rotating ovens with a burner in one end that are used in various industrial processes to heat up materials to high temperatures. The kiln burners are characterized by long diffusion flames where the combustion process is largely controlled by the turbulent diffusion mixing between the burner fuel jet and the surrounding combustion air. The combustion air flow patterns have a significant effect on the mixing and hence the combustion efficiency, motivating a systematic study of the kiln aerodynamics. The objective of this work is to compare turbulence models when modeling the kiln aerodynamics of an iron ore pelletizing rotary kiln. Simulations of the non-reacting isothermal flow using three different ω-based turbulence models are performed on a simplified, down-scaled model of the kiln. Some of the results are validated against particle image velocimetry (PIV) experiments. The turbulence models used are the two-equation shear stress transport (SST) model, the Reynolds stress baseline (RSM-BSL) model and the delayed detached eddy simulation (DDES) turbulence model based on the SST formulation. It is found that the turbulence models produce quite different results yielding various predictions of the flow field. The SST model fails to capture the unsteady behavior of the flow field and the DDES model performs poorly on the grid applied. The Reynolds stress model agrees best when compared with the experimental data and provides a good trade-off between details captured and computational effort.