Turbine Blade Life Prediction Using Fluid-Thermal-Structural Interaction Modelling

The stringent structural requirements posed on aircraft engines, especially the high pressure turbine blades, result from the diversity of the extreme operational conditions they are subjected to. The accurate life assessment of the blades under these conditions therefore demands accurate analytical tools and techniques, and also an elaborate understanding of the operational conditions. Given the drive to reduce cost related to experimental testing, numerical approaches are often adopted to aid in the initial design stages. With recent advancement in numerical modelling, the simultaneous integration of the various numerical codes of fluid flow and structural analysis (otherwise known as fluid-structure interaction) is projected to provide reliable input into fatigue life prediction programs. This study adopts the numerical method of fluid-structure interaction to investigate the fatigue properties of the Aachen turbine test case. A load-time history obtained for the high stress monitor position is superimposed on that from a quasi-static FE solution, and used as input into a fatigue estimation tool. The low cycle fatigue (LCF) is estimated using the Basquin-Coffin-Manson correlation with corrections for mean stress and multi-axial fatigue effects. An FFT analysis of the fluctuating aerodynamic loads show signals with significant high frequency content. There is noticeable increased energy signal at the rotor inlet as compared to stator inlet. The stator inlet signals, however, are characterized by multiple resonances of frequency with lower energy content. By avoiding the resonances, the fatigue analysis predicts a safe design with a safety factor level of 3 for the rotor.