The effects of inlet turbulence intensity levels and computational domains on non-premixed bluff-body flame

The bluff-body stabilized flame provides an ideal case to investigate the interactions between chemical reactions and turbulence. This paper uses CFD to study the effects of inlet turbulence intensity levels for boundary conditions and compare 2D axisymmetric and 3D geometries on the non-premixed turbulent combustion characteristics. The predictive capabilities of the k-å turbulence model are evaluated and compared with the experiments of Correa and Gulati for a bluff-body flame of 27.5%CO/32.3%H2/40.2%N2 and air [1]. The assessment of the modeling techniques with the study of inlet turbulence intensity and between computational domains is compared with experimental profiles. Results showed that the inlet turbulence intensity in the fuel-jet had a substantial impact on the axial decay of mixture fraction and temperature, which did not support the conclusion Correa and Gulati [1] that the flow was relatively insensitive to the inlet profiles. The inlet turbulence intensity of 4% was used to compare the value assumed by Hossain [2] and the results showed a great improvement around the fuel jet inlet and axial profiles. The numerical results of the 2D axisymmetric and 3D domains showed that the 3D domain provided better predictions, which is consistent with Shih et al.[3] that the prediction of axisymmetric jets is unexpectedly poor for the k-å turbulence model due to the underestimation of the dissipation. Further analysis in terms of velocity and strain rate distributions was also conducted to better understand the effects of turbulence intensity levels and computational domains on mixing and fluid dynamics in the reaction zone. Radial velocity results along the centerline provided the reason for the differences between computational domains, for which 2D axisymmetric simulations underestimated the radial velocity magnitude along the centerline. Central profiles of strain rate showed the change of flow and mixing by different turbulence intensity levels.