Swirl control of combustion instabilities in a gas turbine combustor

The impact of premixer swirl number, S , and overall fuel equivalence ratio, Φ , on the stability of a model swirl-stabilized, lean-premixed gas turbine combustor has been numerically simulated using large-eddy simulations methodology. Through the use of a premixed flamelet model ( G equation), unsteady vortexflame and acoustic-flame interactions are captured. It is shown that for large values of S , that is, those sufficiently highly 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. Similar p ′ reduction levels are achieved through changes in Φ . Compared to the leanest equivalence ratio simulated ( Φ =0.52), p ′ at stoichiometric is reduced by 6.0 dB. The response of the combustion process to explicit swirl modulation is also investigated. Open-loop control through swirl variation is demonstrated for a lean mixture with significant reductions in fluctuating mass flow rate and p ′ after a convective time delay.