Thermoacoustic oscillations in can-annular combustors
Final Report Abstract
When a heat source is placed in a cavity, an unwanted acoustic feedback process can occur. This feedback can cause strong vibrations, called thermoacoustic oscillations. These oscillations afflict gas turbines - in which the heat is produced by flames, and the cavity is the combustion chamber - and cause high maintenance costs and increase emissions. The latest generation of gas turbines have can-annular combustors. Each can contain a flame, which combusts in an essentially isolated manner. The cans are however not completely separate from the others, because they are all connected to the turbine stage of the gas turbine through a thin annular section. This section provides a (weak) coupling between the acoustic response of the cans, and can generate peculiar linear structures and nonlinear oscillations. The aero-acoustic interaction between cans and its effect on thermo-acoustic oscillations is not yet well understood, and causes high development costs. Industry invests a lot of time and resources to identify and control thermoacoustic instabilities. The project was motivated by the need of understanding the fundamental causes of thermoacoustic instabilities due to the acoustic interaction between the cans of a combustor. The goal of this project was to identify the main acoustic, thermodynamic and aerodynamic mechanisms causing thermoacoustic instabilities in can-annular systems. The project has been very successful, and has led to the publication of 8 journal articles in high-quality scientific magazines, and the presentation of the results at 5 international conferences. Notably, one of the publications related to this project has won the Best Paper Award at the ASME Turbo Expo 2020 conference, one of the major international events in the sector. Within the scope of the project, we developed mathematical models representing these key mechanisms, and we used them to predict the thermoacoustic behavior of idealized can-annular systems. We have tested our models by comparing their predictions with experimental measurements. Our models can be exploited to understand the thermoacoustic properties of can-annular systems, and used in optimization routines to device control strategies that can be implemented in complex industrial gas turbines. This is a fundamental requirement that will help industry to establish stable operating conditions, resulting in reduced emissions and increased efficiency of gas turbines.
Publications
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A Non-Compact Effective Impedance Model for Can-to-Can Acoustic Communication: Analysis and Optimization of Damping Mechanisms. Journal of Engineering for Gas Turbines and Power, 143(12).
von Saldern Jakob, G. R.; Orchini, Alessandro & Moeck, Jonas P.
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Analysis of Thermoacoustic Modes in Can-Annular Combustors Using Effective Bloch-Type Boundary Conditions. Journal of Engineering for Gas Turbines and Power, 143(7).
von Saldern Jakob, G. R.; Orchini, Alessandro & Moeck, Jonas P.
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Modeling the nonlinear aeroacoustic response of a harmonically forced side branch aperture under turbulent grazing flow. Physical Review Fluids, 6(2).
Pedergnana, Tiemo; Bourquard, Claire; Faure-Beaulieu, Abel & Noiray, Nicolas
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Nonlinear interaction between clustered unstable thermoacoustic modes in can-annular combustors. Proceedings of the Combustion Institute, 38(4), 6145-6153.
von Saldern Jakob, G.R.; Moeck, Jonas P. & Orchini, Alessandro
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An effective impedance for modelling the aeroacoustic coupling of ducts connected via apertures. Journal of Sound and Vibration, 520, 116622.
Orchini, Alessandro
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Coupling-induced instability in a ring of thermoacoustic oscillators. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 478.
Pedergnana, T. & Noiray, N.
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Reduced-order modelling of thermoacoustic instabilities in can-annular combustors. Journal of Sound and Vibration, 526, 116808.
Orchini, Alessandro; Pedergnana, Tiemo; Buschmann, Philip E.; Moeck, Jonas P. & Noiray, Nicolas
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Steady-state statistics, emergent patterns and intermittent energy transfer in a ring of oscillators. Nonlinear Dynamics, 108(2), 1133-1163.
Pedergnana, Tiemo & Noiray, Nicolas
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Acoustics of can-annular combustors: Experimental characterisation and modelling of a lab-scale multi-can setup with adjustable geometry. Journal of Sound and Vibration, 564, 117864.
Humbert, Sylvain C. & Orchini, Alessandro
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Electro-acoustic characterization of annular and can-annular combustors
Sylvain Humbert
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Thermoacoustic oscillations in a can-annular model combustor with asymmetries in the can-to-can coupling. Proceedings of the Combustion Institute, 39(4), 5707-5715.
Buschmann, Philip E.; Worth, Nicholas A. & Moeck, Jonas P.
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Weakly nonlinear analysis of thermoacoustic oscillations in can-annular combustors. Journal of Fluid Mechanics, 980.
Orchini, Alessandro & Moeck, Jonas P.
