Open-loop control of combustion instabilities in a model gas turbine combustor

Abstract

The effect of premixer-induced inlet swirl on the stability of a model swirl-stabilized, lean-premixed gas turbine combustor has been numerically investigated using the large-eddy simulation methodology. The unsteady vortex-flame and acoustic-flame interactions are captured in this study using a thin-flame model that includes an ability to account for the variation in inlet equivalence ratio. Comparisons are made, based on fluid particle trajectories, between the structure of the recirculation regions. It is shown that only for high swirl does a region of flow recirculation, often called vortex breakdown (VB), occur in the centreline region of the dump combustor. This VB region helps to stabilize the flame and results in significant attenuation of the fluctuating pressure amplitudes, p′. The reduced p′ amplitudes are accompanied by reduced longitudinal flame-front oscillations and reduced coherence in the shed vortices. A methodology for open-loop control based on the modulation of incoming fuel-air equivalence ratio is investigated. It is demonstrated that combustor pressure fluctuations respond much more rapidly to these changes compared to earlier studies of inlet swirl number modulation. The impact of these changes on flame stability and overall dynamics is analysed and discussed. Finally, the impact of imperfect mixedness in the incoming fuel-air mixture is also analysed and it is shown that the pressure oscillation amplitude is actually reduced under these conditions. This article is a modified version of the original article from the Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measurements, Mallorca, 16-18 September 2002, which appeared in ‘Engineering Turbulence Modelling Measurements 5’, Elsevier Science, ISBN 0-08-044114-9, ed W Rodi and N Fueyo.