Nonlinear heat release rate response

Experimentally measured (top) and predicted (bottom) evolution of the amplitudes of three simultaneously unstable modes in an experiment with EAF. It is not the mode with the largest (linear) growth rate to dominate the steady-state oscillations, but the (nonlinear) modal interaction at finite amplitudes.

 

Thermoacoustic instabilities can be predicted by means of linear stability theory. When one or more modes are unstable, however, it is the nonlinear response of the heat released by the flame that saturates the instabilities to finite amplitude oscillations. The nonlinear flame response is also responsible for modal interaction when more than one eigenvalue has a positive growth rate, which is common in thermoacoustics. An accurate modelling of the nonlinearity is necessary to predict with accuracy the amplitude of the final states, and to predict which modal structures are observable in real-world experiments.

• PI: Alessandro Orchini
• Funding: Alexander von Humboldt Foundation (2017-2019)
• Collaborators: Prof. Jonas Moeck

S. Humbert, F. Gensini, A. Andreini, C.O. Paschereit, A. Orchini, "Nonlinear analysis of self-sustained oscillations in an annular combustor model with electroacoustic feedback" Proceedings of the Combustion Institute, 2021, Vol. 38, pp. 6085-6093. [link]

J. von Saldern, A. Orchini, J. Moeck, "Nonlinear interaction between clustered unstable thermoacoustic modes in can-annular combustors" Proceedings of the Combustion Institute, 2021, Vol. 38, pp. 6145-6153. [link]

A. Orchini, G. Mensah, J. Moeck, "Effects of nonlinear modal interactions on the thermoacoustic stability of annular combustors" Journal of Engineering for Gas Turbines and Power, 2019, Vol. 141, pp. GTP-18-1356. [link]