Numerical Study of Flame Shapes and Structures in a Two-Stage Two-Injection Aeronautical Burner With Variable Fuel Staging Using Eulerian Large Eddy Simulations

The aim of the present work is to evaluate the ability of large eddy simulation (LES) to predict flame shape and structures in a two-stage two-injection burner representative of new generation staged aeronautical engine: the Banc à Injection Multiple pour les Écoulements Réactifs (BIMER) burner. This combustor is a unique design because of an additional parameter, the staging factor, which controls the fuel mass flow rate splitting between the two swirl stages. Experiments conducted on the BIMER combustor at atmospheric pressure and for a constant power output have revealed that the shape of the flame changes with the staging factor; this shape also depends on the staging factor evolution history (SFEH). Targeting a single operating point and three staging situations, the objectives are to prove the ability of our simulation strategy to predict the proper shapes by reproducing these stabilization processes and to participate in their explanation, using numerical post-treatments. After validation through comparisons with experiments, our study focuses on these three configurations, two of them only differing by their SFEH. Remarkably, correct flame shapes are obtained numerically for the same operating point, fuel staging factors and SFEH. Qualitative and quantitative comparisons show very satisfactory agreement. In a second step, the three flame shapes are analyzed in depth. The key role played by the central and corner recirculation zones in the flames' existence and stabilization processes is emphasized. An original composition space analysis highlights the combustion regimes observed in these three cases, confirming the distinct stabilization scenarios proposed here for the three operating points.