Modelling Thermoacoustic Instabilities With A Graphical Interface Simulink

Modelling Thermoacoustic Instabilities with a Graphical Interface (Simulink)

Combustion units frequently experience thermoacoustic instabilities, also known as combustion oscillations, which are consequence of the internal coupling between acoustic waves and unsteady heat release. Deterioration in system performance, starting by increased emissions or higher levels of fuel consumption, may occur due to this largeamplitude flow oscillations and their associated pressure fluctuations and, under some circumstances, these can be intense enough to cause structural damage on the installation. After introducing its physical background, this acoustic phenomenon is modelled in the time domain using a one-dimensional linearized analytical approach and then implemented into Simulink; thus providing a pioneering tool which models combustion instabilities in an interactive and customizable environment. A first model reproduces the behaviour of an acoustically excited pipe without combustion, whereas a second one simulates the performance of a generic combustor with unsteady heat release without mean flow. The validity of the conceived models is checked through comparison with acoustics theory and earlier research developed in the Laplace domain. This graphical modelling aspires to become a faster, more visual alternative to the complex current approaches to the analysis of combustion oscillations, especially suitable for shorter projects thanks to its simplicity of use. As an initial approach to the interruption of combustion oscillations, feedback control is applied to the modelled combustor. A fixed-parameter controller is designed in the time domain using Nyquist and Bode techniques and then implanted into the Simulink model. Finally, the robustness of the controller to slight changes in the heat release time delay is assessed.

International Aerospace Abstracts

Thermoacoustic Instabilities - Physical Mechanisms and Mathematical Modelling