Influence of Turbulence Modeling on Predictions of Turbulent Combustion

Computations of an axisymmetric bluff-body stabilized turbulent diffusion flame are presented. The effects of turbulence modeling on turbulent combustion predictions are studied. The test case is simulated using κ-e and Reynolds-stress-equation turbulence models with and without extensions for low Reynolds numbers. Turbulent combustion is modeled by two different combustion models with fast chemistry. Effects of chemical kinetics are studied by including detailed chemistry in one combustion model. The combustion predictions are considerably affected by the choice of turbulence model. The nonpremixed flame is stabilized by a recirculation zone behind the bluff body. In isothermal, nonreacting flow, the predictions of the recirculation zone are quite similar for the four models. With combustion, a Reynolds-stress-equation closure predicts a significantly weaker recirculation compared with the κ-e results. This allows a larger spreading of the fuel and better mixing in the bluff-body wake. When finite-rate chemistry is introduced, the κ-e model predicts blow out, whereas the Reynolds-stress-equation model does not. This is due to the larger spreading and mixing by the latter model. The low-Reynolds-number extensions gave a much too strong recirculation, which reduced the spreading of the fuel jet.