Characterization of unsteady pressure behavior utilizing an active flow control method for a lean gas turbine combustor

Active flow control has emerged as a promising strategy for controlling the hydrodynamic instabilities and pressure fluctuations in gas turbine combustors. In this study, fuel feeding excitation (ff) was used as an active control approach, where the fuel supply was modulated at sinusoidal frequencies. These frequencies were arranged as follows: 0 Hz (steady injection), 15 Hz, 50 Hz, 100 Hz, and 200 Hz. Large Eddy Simulations (LES) is implemented as powerful numerical tool to investigate the dynamics of turbulent swirling flows inside the combustor at these fuel frequencies. The results show that the bubble-type vortex breakdown was consistently observed across all excitation frequencies, enhancing the air–fuel mixing process and stabilizing the flame close to the injection region. When the fuel was modulated at a specific frequency, it created periodic disturbances in the model combustor, causing pressure fluctuations in the shear layer, wall, and outlet zones. For instance, at ff = 0 Hz, a strong Precessing Vortex Core (PVC) dictated the flow field behavior, and other instabilities were detected in the shear layer zone. When fuel was modulated at a frequency ff, a strong interaction between fuel modulation and vortex shedding was detected, forcing the pressure fluctuation to follow the wave patterns at the forcing frequency. Moreover, this modulation generated pressure waves that propagate throughout the domain. These waves reflect off boundaries such as walls and the outlet, potentially setting up standing waves. Furthermore, the POD and DMD analysis demonstrates that the pressure oscillation excited powerfully at two zones where the bubble vortex breakdown was formed at the shear layer zone. As a result, a coupling process occurred between the ff and the spiral motion of the PVC, resulting in the formation of an unstable vortical distribution from the shear layer zone.