Azimuthally forced flames in an annular combustor

The application of azimuthal acoustic forcing to flames in a laboratory scale annular combustor is demonstrated in the present paper, which not only allows large amplitude azimuthal modes to be excited, but permits control to be exerted over their frequency, amplitude, and their modal dynamics, including parameters such as the spin ratio and orientation. The effect of forcing frequency is investigated, and it is found that the excitation can be well controlled into a standing wave oscillation over a range of amplitudes for selected frequencies. However, close to the natural frequency of the system, the modal dynamics cannot be well controlled, and instead these tend towards their self-excited state, resulting in a mixed mode. Comparing the phase-averaged structure of the forced and self-excited responses for similar operating conditions, illustrate similar flame dynamics, making this novel forcing approach extremely useful for the study of these instabilities in annular systems.