Stability of azimuthal modes in annular combustion chambers
Résumé
Thermoacoustic instabilities are an important concern in the design of gas turbine combustion chambers. Most modern combustion chambers have annular shapes and this leads to the appearance of azimuthal acoustic modes. These modes are often powerful and can lead to structural vibrations being sometimes damaging. Therefore, they must be identified at the design stage in order to be able to eliminate them. However, due to the complexity of industrial combustion chambers with a large number of burners, numerical studies of real configurations are a challenging task. The following work shows results obtained on an industrial annular gas turbine combustor with 24 burners using an acoustic approach. Assuming that each burner does not interact with the adjacent ones and is influenced only by the fluctuations of the flow rate through it, the Flame Transfer Function (FTF) of a single burner can be calculated via a single burner LES and used to simulate the acoustics of the 360° geometry (24 burners). This approach allows to predict stability changes when the flame is modified and to propose combustor modifications increasing the stability of the engine.