Modeling and analysis of high-frequency thermoacoustic oscillations in gas turbine combustion chambers

Gas turbines have been playing a key role for electrical power generation in the past decades. The importance of this role is expected to increase in the future, which is due to two main reasons. First, gas turbines are a central component within high-efficiency combined cycle power plants for electricity generation that emit considerably less carbon dioxide than e. g. coal-fired plants. Second, gas turbines are suited for compensating load fluctuations in the electric grid induced by fluctuations of renewable energy sources. This compensation role is due to gas turbines' capabilities of fast and flexible changes between operation points, fuel types and load level while maintaining a low-emission combustion process at optimal efficiencies. In order to comply with stringent emission regulations (particularly carbon monoxide and nitrogen oxides), lean premixed combustion technologies are employed. These technologies, however, cause the combustion chambers to be sensitive to develop thermoacoustic instabilities. The main focuses of this thesis is on thermoacoustic instabilities that are specifically characterized by high-frequency screech tones. In this frequency regime, thermoacoustic interactions between flame and acoustic modes are spatially variable, i. e. non-compact. As an overall research objective, a comprehensive modeling framework for analysis of high-frequency thermoacoustics in gas turbine combustors is developed. This framework is validated by conducting respective modeling and analysis tasks of a lab-scale swirl-stabilized combustor. From the results, understanding of physical mechanisms as well as system behavior of high-frequency instabilities at the first transversal mode in gas turbine combustors is deduced.