Turbine Blade Tip Shroud Offset to Shift Flutter Modes
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Solution Overview
Problem
Gas turbine blades experience flutter due to vibratory motion, which can lead to damage, and existing shroud designs do not adequately prevent this, allowing operation near the flutter threshold.
Innovation Solution
A turbine blade shroud configuration with a knife edge offset from the mid-chord point to alter modal responses, reducing susceptibility to flutter by positioning the modal response outside the operating speed range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shroud is added to the blades to reduce vibrations and seal the blade tip region, then blade vibration damping is improved and hot combustion gases are prevented from leaking, but the blades can still operate at or near the threshold for flutter
Solution Approach 1:
The patent applies parameter changes by modifying the spatial position of the knife edge seal relative to the mid-chord point. Specifically, the knife edge is positioned at a location that changes the modal response characteristics of the blade, moving the resonant frequency away from the operating speed range. This positional parameter change transforms the blade's vibrational characteristics to reduce flutter susceptibility while maintaining the sealing function.
2Reliability
If the knife edge seal is positioned at the mid-chord point, then the sealing function is optimized, but the modal response may fall within the operating speed range causing flutter
Solution Approach 1:
The patent employs asymmetry by deliberately positioning the knife edge seal offset from the mid-chord point rather than at the symmetric mid-chord location. This asymmetric positioning changes the moment of inertia and vibrational characteristics of the blade, shifting the modal response to frequencies outside the operating range. The asymmetric design trades perfect sealing symmetry for vibrational stability.
3Object-affected harmful factors
If the modal response is positioned outside the operating speed range, then flutter resistance is improved, but the sealing effectiveness may be compromised
Solution Approach 1:
The patent applies local quality by concentrating the sealing function at a specific localized position (the knife edge) while using the overall blade-shroud assembly to provide the sealing effect. The knife edge creates a localized seal at the critical blade tip region, and the offset positioning is optimized to simultaneously achieve both flutter resistance and effective sealing at that local position.
Data Source
AI summary
A gas turbine blade for a gas turbine engine includes an attachment, a blade neck portion, a platform, an airfoil, and a shroud. The gas turbine engine has an operating speed range. The blade neck portion extends radially outward from the attachment. The platform is attached to the blade neck portion opposite the attachment. The airfoil extends radially outward from the platform. The airfoil includes a leading edge, a trailing edge, and an axial chord defined between the leading and trailing edges. The axial chord defines a mid-chord point. The shroud is attached to an end of the airfoil. The shroud includes an upper surface and a modal response tuning component attached to the upper surface of the shroud. The modal response tuning component is offset from the mid-chord point a predetermined distance to move modal response of the gas turbine blade outside of the operating speed range.