Conference Paper

Fatigue Life Consumption for Turbine Blades-Vanes Accelerated by Erosion-Contour Modification

Conference: 2011 International Conference Of Fluid Mass And Heat Transfer, ICFMHTT-2011, Volume: print ISSN 2010-376X, electronic ISSN 2010-3778


A new mechanism responsible for structural life consumption due to resonant fatigue in turbine blades, or vanes, is presented and explained. A rotating blade or vane in a gas turbine can change its contour due to erosion and/or material build up, in any of these instances, the surface pressure distribution occurring on the suction and pressure sides of blades-vanes can suffer substantial modification of their pressure and temperatures envelopes and flow characteristics. Meanwhile, the relative rotation between the blade and duct vane while the pressurized gas flows and the consequent wake crossings, will induce a fluctuating thrust force or lift that will excite the blade. An actual totally used up set of vane-blade components in a HP turbine power stage in a gas turbine is analyzed. The blade suffered some material erosion mostly at the trailing edge provoking a peculiar surface pressure envelope which evolved as the relative position between the vane and the blade passed in front of each other. Interestingly preliminary modal analysis for this eroded blade indicates several natural frequencies within the aeromechanic power spectrum, moreover, the highest frequency component is 94% of one natural frequency indicating near resonant condition. Independently of other simultaneously occurring fatigue cycles (such as thermal, centrifugal stresses).

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Available from: Julio C Gomez-Mancilla,
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    ABSTRACT: Blade vibrations, with the possibility of a failure, are one of the major factors controlling the reliability of all compressors and turbines. Flow disturbances upstream and downstream of rotor/ stator will produce wake pulses that excite the blades. This requires a structural dynamic model of the blade stress response for a given excitation and a method to estimate the pulsating forces acting on the rotating blades by the stationary components and, vice versa, for rotor pulsations acting on the stator. This paper discusses the efforts made to understand the aerodynamic instabilities caused by the vane and its role in generation of blade vibration. Here, comprehensive computational fluid dynamics (CFD) are used to get a better understanding of the stator-rotor flow interactions at different operating conditions and their effect on overall pulsation and vibration levels. This model is based on blade dynamic response measurements and on careful CFD simulations of basic flow altering scenarios. It is found that a surprisingly low misalignment angle (relative) could result in fatigue damage stress levels in most cases. This paper presents several example cases to demonstrate typical flow profiles for axial and radial compressors/ turbines with varying stator flow distortions. It is Part 1 of a two-part high cycle fatigue (HCF) failure analysis procedure, dealing with aerodynamic excitation aspects.
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