Conjugate Heat Transfer Study of a Spin Pit Rig: Application to the Lifing of HP Turbine Disc Firtrees

Structural life and durability of gas turbine engine discs and blade firtree has always been a key design issue for designers and technologists. This is particularly important for gas turbine components which operate at elevated temperatures under high loads. The testing for these components need to be undertaken at operating conditions, particularly when Low Cycle Fatigue (LCF) lives of components are evaluated. The spin pit and biaxial rig tests, the former of which is the concern of this study, are used in the aero gas turbine industry for the lifing analysis of these critical engine parts. In this study a three dimensional conjugate heat transfer analysis of the spin pit rig with the HP turbine disc and blade assembly for a large turbofan engine has been performed. The scope of the Computational Fluid Dynamics (CFD) analysis has allowed a detailed understanding of the flow and thermal field within the domain to be obtained. Flow within the rig was found to be complex, with multiple flow mechanisms simultaneously at play in several distinct areas of the solution domain. All heat transfer processes, radiation, convection and conduction were found to be important in the overall heat. Radiation heat transfer was found to be dominant in terms of temperature levels achieved in components, whilst convection heat transfer majorly influenced temperature gradients in solids. The appropriate capturing of flow leakages in the rig proved to have a significant impact on rig performance and component thermal fields. The component temperatures predicted by the tuned CFD model compared well against thermocouple measurements and predictions of the conjugate CFD analyses were directly used as boundary conditions in follow-on stress analyses for lifing purposes. The methodology adopted has resulted in a very satisfactory outcome on declared disk life. It is understood that this is the first time where a full conjugate heat transfer CFD study of the spin pit rig without any separate thermal analyses, has been applied directly to the lifing of HP disc firtree and the eventual engine certification, in the aero gas turbine industry.