Synchronization of Low-Frequency Thermoacoustic Oscillation in Can-Annular Combustor via Compressor Combustion Casing

Thermoacoustic instability remains an important challenge in gas turbines. In can-annular combustors, cross-talk effects can lead to complex collective dynamics. This paper investigates the in-phase synchronization of low-frequency thermoacoustic oscillations in a can-annular combustor, focusing on the upstream cross-talk mechanism mediated by the compressor combustion casing. Dynamic pressure data from the full-scale engine reveal a transition from independent, low-amplitude pressure dynamics to a state of high-amplitude, in-phase synchronized oscillation in the combustor system. To quantify the upstream cross-talk effect, the multi-port acoustic scattering matrix of the casing is computed by solving the Helmholtz equation based on a mean-flow field obtained from Reynolds-Averaged Navier–Stokes simulations. Analysis of the matrix shows that the casing provides a coupling path between cans, with strength and phase being insensitive to the relative azimuthal position of the cans. Based on this physical insight, a star-network model of coupled Van der Pol oscillators is developed. The model, with parameters identified from experimental data and inferred from the scattering matrix, successfully reproduces the synchronization phenomenon observed in the experiment. A subsequent parametric study based on the validated model shows that in-phase synchronization occurs within periodic windows of the time delay and that the range of these windows expands with increasing coupling strengths. For τ=0.1T, 0.85T and 1.1T, synchronization is achieved with moderate coupling strengths. For τ=0.35T and 0.6T, the interaction between the two coupling mechanisms suppresses synchronization even at strong coupling strengths. This study shows that the upstream cross-talk effect is an important mechanism for in-phase synchronization and provides a validated, physics-based model for analyzing and predicting the collective thermoacoustic behavior of can-annular combustors.