The present study experimentally investigates the transition from the state of combustion noise (CN) to thermoacoustic instability (TAI) in a turbulent annular combustor. Annular combustors are typically used in gas turbine and aircraft engines to generate thrust for propulsion. These combustors are prone to the occurrence of ruinously large-amplitude pressure oscillations resulting from positive feedback between the acoustic pressure oscillations and the heat release rate fluctuations of the flames. The lab-scale combustor used in this study consists of sixteen premixed swirl-stabilized flames arranged around an annulus. We simultaneously measure the acoustic pressure and CH* chemiluminescence emission of the flame using a high-speed camera. We demonstrate that the criticality of Hopf bifurcations is decided by the stabilizing or destabilizing nature of the dominant nonlinearities in the system when the control parameters such as flow rate and equivalence ratio are varied. We observe different states with distinct dynamics when a control parameter is varied. These dynamical states include the states of combustion noise (CN), intermittency (INT), low-amplitude TAI (LA-TAI), mixed-mode oscillations (MMO), and high- amplitude TAI (HA-TAI) from LA-TAI through a secondary bifurcation. We report the first evidence of secondary bifurcation from LA-TAI to HA- TAI in a turbulent thermoacoustic system. We finally discuss the global flame dynamics during intermittency associated with
the longitudinal mode of the combustor.