Implications of military aircraft’s mission optimal performance on gas turbine engine life expectancy

Gas turbine engines have a crucial role in evaluating military aircraft performance. Operating in a range of missions and environmental conditions, they are subjected to an excessively demanding usage often reaching their operating limits. The impact prediction on engine components degradation of this adverse usage requires a multi-disciplinary approach to best capture its effects. This master thesis investigates the implications of optimal mission performance on the degradation of military gas turbine engines. The research focuses on the degradation of first stage of the high-pressure turbine caused by the failure mechanisms of creep, low cycle fatigue and high cycle fatigue, each acting independently on the turbine blades. By exploring the implications of mission performance on engine degradation, this study provides valuable insights for optimizing mission execution strategies and improving operational efficiency in military aviation. Through a comprehensive analysis, several key findings have been identified. It was observed that as the turbine entry temperature (TET) decreases, the stresses on the turbine blade have a disproportionately greater effect on the overall damage. This suggests that maintaining optimal TET levels is crucial for mitigating engine degradation, as an increase of 0.005% in blade temperature can lead to 40% more thrust, 100% more fuel consumption but can reduce life by 18% in Creep, 15% in LCF and 14% in HCF. In addition, the study reveals that the use of afterburner though having similar thermo-mechanical stresses upon the blades with the maximum dry setting, the extensive usage in a mission can significantly impact the life consumption. A mission with 40% less overall duration can present an up to 40% reduced life expectancy. Lastly, the investigation highlights the significant differences in life consumption during several optimal climb paths. A time optimized profile is found to be the most damage inflicting having 3 times less lifespan than noise and IR optimized paths. A life expectancy of only 80 flight hours is predicted for the usage applied on this profile resulting from the impact of low cycle fatigue contribution. This research contributes to the field of military-related costs by shedding light on the operational availability of gas turbine engines.