On Wednesday, 26 August 2015, a seminar on the 'Thermoacoustic Instabilities in Annular Combustion Chambers: Linear and Non-Linear Phenomena' by Prof. Jonas Moeck was hosted at the Clean Combustion Research Center. The abstract of the seminar is given below:
Thermoacoustic instabilities frequently appear in various combustion systems in the form of high-amplitude pressure oscillations. This undesirable dynamic phenomenon that originates from the interaction of unsteady heat release rate and the acoustic modes of the combustion chamber has been particularly plaguing for the development of low-emission gas turbine technology. After a brief introduction to the topic, Prof. Moeck discussed some aspects that are specific to annular combustion chambers, as they are found in aeroengines and in most gas turbines for power generation. These combustors exhibit some special dynamical features associated with their discrete rotational symmetry. After introducing the key aspects of the linear properties of thermoacoustic modes in this type of system, he presented a new, efficient modeling approach that fully exploits the discrete rotational symmetry to compute linear stability properties. This technique is applied to determine thermoacoustic modes in an industrial gas turbine combustor and gives results in excellent agreement with a full computation. At finite amplitude, when the flame response saturates, additional phenomena appear, such as the existence of multiple limit cycle solutions or the nonlinear interaction of modes in the form of synchronized two-mode oscillations; the latter is shown to give rise to a slanted mode pattern, which was recently observed in experiments. These phenomena can be qualitatively modeled using coupled nonlinear oscillator models. He also presented some recent results based on this approach.
Jonas Moeck is an Assistant Professor of combustion dynamics at the Technical University of Berlin. He received his engineering degree and PhD also from the Technical University Berlin and had a postdoc position at Ecole Centrale, Paris. His research focuses on flame dynamics, active control of combustion instabilities, and low-order modeling and stability analysis.