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

The impact of premixer swirl number, S, on the stability of a model swirl-stabilized, lean-premixed gas turbine combustor has been numerically simulated using Large-Eddy Simulations (LES) methodology. Through the use of a premixed flamelet model (G-equation), unsteady vortex-flame and acoustic-flame interactions are captured. It is shown that for large values of S, i.e. those sufficiently high for Vortex-Breakdown to occur, the fluctuating pressure amplitudes, p', are attenuated significantly (over 6.6 dB reduction). The reduced p' amplitudes are accompanied by reduced longitudinal flame-front oscillations and reduced coherence in the shed vortices. A methodology for active control based on modulation of S is also investigated. Open-loop control through S variation is demonstrated for a lean mixture with significant reductions in fluctuating mass-flow-rate and p' after a convective time-delay.