Analysis of the local equivalence ratio under fuel-feeding excitations in a lean gas turbine model combustor: Large eddy simulation approach

Abstract

The synchronization process between the fuel-feeding excitation (ff) and the local equivalence ratio (ϕlocal) is a key issue that has not been well studied numerically under lean conditions. Therefore, in this study, a large eddy simulation (LES) with a wall-adapting local eddy-viscosity (WALE) subgrid model was utilized to analyze the interaction between various fuel-feeding excitations and the local equivalence ratio in a lean partially premixed gas turbine model combustor. The model combustor was simulated using five values of fuel-feeding excitation: 0 Hz, 15 Hz, 50 Hz, 100 Hz and 200 Hz. The results demonstrated that the complex interaction between the swirling flow and the fuel-feeding excitation affected the flow structure. These changes enhanced the excitation of toroidal counter-rotating vortices in the region between the fuel jet exit and shear layers, which improved the homogeneity of ϕlocal inside the inner recirculation zone (IRZ). Furthermore, the fuel-feeding excitation modulated the shear layer thickness by increasing the rolling-up of the instantaneous counter-rotating vortices, leading to spatial regularity for ϕlocal inside the IRZ. The coupling process between the fuel-feeding excitation and the precessing vortex core (PVC) significantly increased the fluctuations of ϕlocal around the fuel jet exit and the shear layer region. An analysis of the probability distribution showed a nonlinear relationship between ff and ϕlocal, where ϕlocal was high when ff = 50 Hz, enhancing the uniformity of ϕlocal inside the IRZ. However, ϕlocal was more spread radially when ff = 0 Hz in the downstream direction. The merging of vortex shedding and the PVC increasingly excited the self-oscillation of ϕlocal, while the fuel-feeding excitation dominated the oscillation of the counter-rotating vortices by increasing the subharmonic vortices. Moreover, the fuel-feeding excitation controlled and organized the small vortical structures, leading to stabilization of ϕlocal when ff = 50 Hz, 100 Hz, and 200 Hz.