Onset of Thermoacoustic Oscillations in an Annular Combustor with Flames Stabilized by Circular Discs

This chapter examines the onset of thermoacoustic oscillations in an annular combustor. The combustor consists of 12 burners with flames stabilized in the flow path using circular discs. The premixed fuel and air are used in the present investigation to scrutinize the observed thermoacoustic oscillations. The acoustic pressure fluctuations acquired in this combustor exhibit two dominant peaks. These peaks occur at 664 and 331 Hz, associated with the first azimuthal-first longitudinal (1A-1L) and first longitudinal acoustic modes, respectively. The combustor dynamics are examined by keeping the fuel flow rate constant with varying the air flow rate. The combustor exhibits non-monotonic variation in acoustic pressure amplitude, with intermediate air flow rates showing relatively large amplitude acoustic pressure fluctuations. Further, we observed a difference in amplitude envelope between the increasing and decreasing airflow rates, illustrating the occurrence of subcritical bifurcation. In addition, the phase space, first return map and recurrence plots are used to characterize the transition from relatively low amplitude to large amplitude acoustic pressure fluctuations.