Masterarbeit

Thermoacoustic instabilities arise due to the constructive feedback between unsteady heat release fluctuations and combustor acoustics. They are strongly undesirable, as they lead to unwanted structural vibrations, thus limiting the operating range of the engine. The last generation (H-class) of gas turbines features can-annular combustor architectures. In these combustors, each flame burns in an essentially isolated manner in a can. A dozen of cans are placed azimuthally, without any aerodynamic coupling between the cans. Nonetheless, the annular turbine inlet, which is shared by all cans, couples the cans via acoustic phenomena. On an abstract level, the thermoacoustic dynamics of a can-annular combustor can then be characterized as a ring of weakly coupled self-excited oscillators. One oscillator represents an acoustic mode of an isolated can, driven by its flame, and weak coupling is provided by the gap between two cans at the turbine inlet. Experimental observations in real system recently shown that both global and localized self-sustained thermoacoustic modes can occur.

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