A study on the response characteristics of flow variables in a swirling flow field with fuel excitation frequency in gas turbine combustors

Large eddy simulation (LES) is employed to investigate the influence of periodic fuel-feeding ( f _f ) excitation on the unsteady flow dynamics of a lean, partially premixed swirling gas turbine combustor under non-reacting (isothermal) conditions. The flow response to periodic fuel modulation is evaluated through the distributions of pressure, velocity, and equivalence-ratio fields along the shear layer and recirculation regions. Interaction between the swirling flow and the imposed excitation generates toroidal counter-rotating vortices between the fuel jet exit and the shear layer, improving local equivalence-ratio homogenization within the recirculation zone. Dynamic coupling between upstream fuel perturbations and downstream flow structures is quantified using time-lag and spectral analyses, revealing convective propagation of disturbances along the shear layer. Transfer-function analysis shows bounded amplitude gain and high coherence at the forcing frequencies, indicating that the imposed perturbation interacts with intrinsic shear-layer dynamics without inducing resonant hydrodynamic growth. Instead, forcing modifies the organization of coherent hydrodynamic structures associated with the precessing vortex core (PVC). Nonlinear diagnostics based on phase-space reconstruction capture the temporal evolution of flow attractors, while recurrence quantification identifies repeating dynamical patterns and deterministic structure in the velocity and equivalence-ratio fields, with pressure fluctuations exhibiting comparatively lower nonlinear complexity. Proper orthogonal decomposition further highlights the dominance of PVC-related modes and the redistribution of energy among coherent structures under periodic excitation. These findings provide insight into hydrodynamic mechanisms governing forced swirling flows and support the development of fuel-modulation strategies for improved flow control in gas turbine combustor configurations.