Aeromechanical Design of Damped High Pressure Turbine Blades Subject to Low Engine Order Forcing

摘要

Avoidance of High Cycle Fatigue (HCF) problems in Turbomachinery imposes one of the major constraints when optimizing the design of Turbine Blading. Aerodynamic design can be compromised and specific mechanical design features are added purely to control dynamic characteristics and minimize vibration. A typical basic strategy would seek to minimize exposure to resonances of concern, minimize excitation forcing, maximize damping and maximize HCF strength of the component. A strategy such as this normally relies on data from Forced Response analysis where unsteady pressure amplitude & phase is predicted from a CFD code, combined with the structural model information, Mass (M), Stiffness (K), Damping (C) and fed into transient dynamics software. It is vital however that when choosing for example the optimum mass for an underplatform friction damper all potential resonances are accounted for and that this mass should be fixed a long time in advance of any engine vibration survey. The chosen optimum mass will be a compromise between the optimums for each resonance of concern and also taking into account any interactions between modes. The current paper addresses this problem by investigating a number of alternative simplified approaches, calibrated against a full multi passage analysis drawing comparisons with actual strain gauge results from an engine vibration survey for a damped High Pressure Turbine Blade. The methods investigated range from simple point forces applied at aerofoil center of pressure to various assumptions about the pressure amplitude and phase. The paper discusses the relative accuracy and applicability bounds of the simplified methods and makes suggestions for further research.