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Thermo-acoustic instabilities

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 generation of sound and structural vibrations, limiting the operating range of the engine and, in extreme scenarios, can lead to mechanical failures. Their prediction and control is of paramount importance for the safe operation of both aeroengines and land-based gas turbines for power generation.



Although thermoacoustic instabilities have been observed since long time, their accurate prediction is a challenging scientific and engineering task, and they continue to plague the development of new technologies. For example, 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. Nonetheless, the annular turbine inlet, which is shared by all cans, couples the cans via acoustic phenomena. These coupling causes the formation of thermoacoustic eigenvalue clusters, which does not occur in classic annular architecture. Another example of paramount importance is the recent advent of hydrogen-fuelled gas turbines. Hydrogen combustion is particularly susceptible to thermoacoustic instabilities, and little is known about the scaling properties of hydrogen at increasing pressure in this regard.

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