LES of chemical and acoustic forcing of a premixed dump combustor

This paper describes the first steps in the development of a large eddy sim ulation (LES) code able to compute combustion instabilities in gas turbines . This code was used to compute the forcing of an experimentally investigat ed premixed dump combustor. It is shown that the main effect of acoustic wa ves entering the combustion chamber is to create large vortices and unstead y heat release when these vortices burn. Another effect of waves entering t he combustor is to modulate the fuel and air flow rates produced by the fee ding lines. In this case the equivalence ratio of the mixture entering the combustor may also vary. This was investigated in a "chemical effect" simul ation where the inlet equivalence ratio fluctuates but the total flow rate remains constant. For perturbations from stoichiometric burning, this mecha nism was shown to induce less destabilizing effects than the purely aerodyn amical mechanism due to vortex formation and combustion. It is shown that t he LES methodology developed is able to reproduce the experimentally observ ed phase shift between acoustic excitation and total reaction rate in the c hamber.