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Thermoacoustic instabilities in can-annular combustors



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.


Thesis description

This work will be performed through numerical simulations and theoretical modelling. Low order models (with 1D or 2D acoustics) based on the coupled response of a can-annular system, will be derived to explain the occurrence of thermoacoustic oscillations in can-annular combustors. The focus of the research will be on the linear and nonlinear effects that acoustic coupling has on the can-annular system response. The linear response will be deduced from theoretical models in the frequency domain.

The research outcome has the potential to be published in major scientific journals.

Your profile

I am looking for a motivated and creative student, happy to work in a team and with good communication skills. Applicants for this position are expected to have a background in Mechanical Engineering or Physics, and about to finish their Master's studies. Ideally, you have experience in one or more of the following: nonlinear dynamics, acoustics, transfer functions.


Now! (23.07.2020)


Dr. Alessandro Orchini


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