Low-Order Modeling to Investigate Clusters of Intrinsic Thermoacoustic Modes in Annular Combustors

Abstract The intrinsic thermoacoustic (ITA) feedbackloop constitutes a coupling between flow, flame and acoustics that does not involve the natural acoustic modes of system. One recent study showed ITA in annular combustors come significant number with peculiar behavior clusters, i.e. several close frequencies. In present work, an analytical model typical combustor is derived via Riemann invariants Bloch theory. resulting formulation describes full system as longitudinal outlet reflection coefficient depends on frequency azimuthal mode order. explains underlying mechanism clustering phenomena structure clusters associated different orders. addition, phasor analysis proposed, which encloses conditions for 1D remains valid when describing combustor.