Investigation of the TECFLAM Non-premixed Flame Using Large Eddy Simulation and Proper Orthogonal Decomposition

The confined turbulent swirling non-premixed TECFLAM S09c flame has been investigated using Large Eddy Simulation and a pre-calculated mixture-fraction-based flamelet model in a preliminary step to simulate this flame. The simplified formulation, despite the fact that it cannot capture localized extinctions, is found to reproduce the experimentally-observed vortex breakdown and the results agree well with available experimental data for velocity and mixture fraction. The unsteady flow features before the burner exit and inside the combustion chamber are analyzed with spectral analysis, correlations, and Proper Orthogonal Decomposition. The results show the presence of longitudinal vortices whose axes rotate with the swirl and which cause separation inside the inlet pipe. With combustion, some of the structures are damped and the spectral peaks shift to higher frequencies. Finally, simulations with the full 3D Conditional Moment Closure equation, which allows spatial and temporal fluctuations of the conditionally-filtered reacting scalars, reproduce successfully the flame lift-off observed experimentally.