Environmental regulations are continuously pushing lower emissions with an impact on the combustion process in gas turbines (GT). As a consequence, GT combustors operate in very lean regimes (i.e. at relatively low temperature) to reduce NOx formation. Unfortunately, stabilization becomes a challenge for these lean premixed flames. The extremely unsteady dynamics of swirl stabilized flames present crucial issues and this investigation aims at understanding the interaction of swirl stabilization with large coherent fluctuations inherent to vortex breakdown.
The investigation utilizes a simplified cylindrical model combustor consisting of a premixing tube discharging in a larger combustion chamber. Fuel and swirling air are injected separately in the mixing tube so that a partially premixed swirling jet encounters vortex breakdown and allows the partially premixed flame to stabilize. The aforementioned extreme sensitivity of lean partially premixed flames challenges any investigation either for measuring, simulating or post-processing the case of interest.
In this paper, the problem is addressed using large eddy simulation (LES) and planar laser induced fluorescence. The LES data are used to follow the fuel air/mixing as well as the fuel combustion evidencing large-scale dynamics. These dynamics are further investigated using Proper Orthogonal Decomposition to identify the role of the premixing stage and of the Precessing Vortex Core in the flame behaviour.