Experimental study on acoustic and flame responses in an annular combustor under azimuthal force

Abstract

This study investigates the flame dynamics of an annular combustor under various azimuthal acoustic forces. The experimental platform was applied to external azimuthal acoustic force through four loudspeakers installed on the wall outside the plenum. Experiments were conducted with an equivalence ratio of Ф = 0.71 and a combustion power of P = 9.5 kW. Therein, four loudspeakers were used to precisely control the acoustic pressure amplitude, spinning ratio, and spinning direction, which stimulated the first-order standing mode, spinning modes, and second-order standing mode acoustic mode of the plenum, respectively. Our analysis of flame dynamics and acoustic response characteristics was based on different azimuthal modes, combined with dynamic mode decomposition (DMD) of the flame image sequence and acoustic pressure signal. The results corroborate the consistency between the acoustic field quaternion analysis and the flame image sequence DMD results despite varied external forcing conditions. Specifically, the characteristics of the flame vary by the applied forces. Moreover, DMD results indicate that the flame structure of the eigenfrequency mode is asymmetrical in spinning modes and tilts in the direction of the pressure gradient.