The analysis of mechanical integrity in gas turbine engines subjected to combustion instabilities

Stringent regulations have been introduced towards reducing pollutant emissions and preserving our environment. Lowering NOx emissions is one of the main targets of industrial gas turbine engines for power generation. The combustion zone temperature is one of the critical parameters, which is directly proportional to NOx emission levels. Premixing an excessive amount of air with fuel before delivering to the combustor can reduce the temperature, at which combustion takes place, by burning a leaner mixture. Therefore, new generation combustion systems for modern gas turbines have been introduced, which are named lean, premixed (LP) combustion systems. However, LP combustion systems are prone to thermo-acoustically induced combustion instabilities, which are excited by a feedback mechanism between heat release, pressure and flow-mixture oscillations. Consequently, high amplitude oscillations of pressure are generated and heat transfer is generated, which results in mechanical vibrations at elevated temperatures, and hence degradation of mechanical integrity of combustor components due to fatigue and creep damage. The present work in this thesis is focused on the development of efficient analysis tools to investigate the sensitivity of mechanical integrity and to assess the lifetime of structures at combustion instabilities.