We address highly swirling, confined-bluff-body-flow evolving through a burner; particularly, contributions of the swirling motion to a central-recirculation-zone (CRZ) downstream the injector. Previous studies suggest that flame stability reduces in combustors lacking this zone; careful consideration of the CRZ is thus desirable. We use Reynolds-Averaged-Navier–Stokes (RANS) and Large-Eddy-Simulation (LES) to simulate the flow, and the influence of the swirl device was included in defining the inflow conditions for LES simulations. We use mean velocity profiles and turbulence statistics to test results. There is qualitative agreement between computed and reported experimental data, and we document quantitative differences obtained with the RANS models. LES velocity field results are mostly within 3% of the experimental data, better than the latest reported LES data, reinforcing the suitability of our approach. We took advantage of the quality of the LES mesh, which solves 95.6% of the resolved-turbulence-energy, to present the vorticity structures showing the precessing vortex motion on the CRZ boundaries. Anisotropic states of the Reynolds-stress were characterized with the aid of an anisotropy invariant map, a novelty for this type of burner; the turbulence states considerably vary inside the burner, behaving isotropically in the center of the CRZ, whereas axisymmetric turbulence is predominant in the other areas of the CRZ. The results reinforce the importance of applying appropriate turbulence models and inflow conditions for simulations involving confined-bluff-body-flows in order to capture the main flow fields and structures in the CRZ.

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We undertake the modeling of the combustion of highly swirling fuel sprays using the Flamelet-Generated-Manifold (FGM) combustion-chemistry-reduction technique, especially the use of adiabatic tables generated with non-premixed chemical reactors. Preceding investigations indicated that tables thus generated can present uncertainties when used for predicting the finite-rate phenomena and different flame modes, and these are important for better prediction of spray flames in gas turbines. Thus, to address these, we have adopted a mixed-homogeneous chemical reactor that is applicable to both pre-mixed and non-premixed reactions and evaluated this using detailed computations of a constant-pressure mixed reactor. In addition, we have included curated levels of flame-liquid heat gain and loss in the generation of the FGM libraries and analyzed the effects on the major species formation. The methodologies were then incorporated into a Reynolds-averaged-Navier-Stokes model to analyze the data from the reacting ethanol spray flames, and the results were tested against the values of the mixture fraction at axial locations, the burner power output, the flame heat release structure, and the mean of the flame lift-off. The computed burner power output and mean flame lift-off were ∼90.4% and ∼89.6% of the reported experimental data, respectively. Compared with the newest published large-eddy-simulation data, the predictions for the mixture fraction values especially at the center of the flame in the central-recirculation-zone were not underestimated, and the spatial distribution of the flame OH captured the flame height and shape better. The inclusion of mixed homogeneous reactors and flame-liquid heat transfer in FGM can enhance their use in spray-combustion studies.

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