This paper describes an experimental and theoretical investigation of the processes controlling the characteristics of limit cycle oscillations in an unstable gas turbine combustor. Specifically, this paper describes an analysis of the cycle-to-cycle variations in the phase of the oscillating pressure during an instability. It is shown that the phase of the combustor pressure oscillations continuously drifts in a predominantly irregular manner. It is also shown that this phase drift may primarily be caused by random processes (i.e., noise) and, thus, may not reflect any of the underlying dynamics of the instability. Finally, it is shown that deterministic factors appear to have a small affect on the phase variability that manifests itself as slow, approximately 1.4 Hz oscillation of the phase. It is concluded that analysis of “steady state” limit cycle pressure data may not provide the desired information about the nonlinear processes controlling the system’s dynamics because of the affects of background noise.

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