We present an experimental investigation of the mutual synchronization between hydrodynamic and thermoacoustic oscillations in a turbulent lean-premixed bluff‐body flame. By fixing the equivalence ratio ($\varphi =0.65$) and Reynolds number ($\mathrm{Re}=5.4\times {10}^3$) and systematically varying the combustor length, we sweep the acoustic chamber eigenfrequency through the hydrodynamic vortex-shedding frequency. As the combustor length increases, the system evolves from a pure hydrodynamic vortex-shedding mode, through a thermoacoustically self-excited combustor mode, to a hybrid quasiperiodic state in which both modes coexist, and finally to a 1:2 mutually synchronized state in which both modes lock together, amplifying both the heat release rate (HRR) and pressure oscillations. Temporal analyses–Hilbert‐transform metrics, recurrence quantification, and Pearson correlation–reveal the route from desynchronization to phase and generalized synchronization, the latter coinciding with a significant amplification of the HRR and pressure amplitudes. Spatiotemporal analyses—local frequency and HRR amplitude maps, Rayleigh index fields, phase-locking distributions, and modal decomposition of ${\mathrm{CH}}^{*}$ chemiluminescence images—reveal the bluff‐body recirculation zone as the dominant energy-injection site for thermoacoustic instability. Finally, two flame blow-off pathways are identified: (i) isolated pinch-off events that cause global extinction when $\varphi$ drops below the lean flammability limit and (ii) coupled pinch-off/wall-quenching events driven by high-amplitude thermoacoustic forcing. These findings clarify the interplay between hydrodynamic and thermoacoustic modes, guiding control strategies for next-generation low-emission combustors.

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• Combustion
• Reacting flows
• Synchronization
• Turbulent reacting flows
• Vortex shedding