Variable Stator Vane Biconic Button Undercut Design
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Solution Overview
Problem
Conventional variable stator vane buttons in aircraft gas turbine engines face limitations due to their size, leading to endwall leakage and flow non-uniformities, which result in increased losses and potential rotor blade vibrations, as they cannot effectively cover the entire vane chord and maintain aerodynamic efficiency across varying operating conditions.
Innovation Solution
The design incorporates a biconic button with a cylindrical portion and a radially inwardly extending conical undercut, allowing for a larger diameter and reduced airfoil overhang, which supports the airfoil and maintains aerodynamic shape without introducing gaps or steps, enabling better endwall coverage and reduced leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional VSV buttons with diameter equal to or slightly less than pitchwise spacing are used, then the buttons can be fitted together without overlap, but endwall leakage increases and aerodynamic efficiency decreases
Solution Approach 1:
The button design transitions from a simple cylindrical shape to a biconic configuration with an undercut portion. This dimensional change allows the button to extend radially inwardly beneath adjacent buttons, increasing endwall coverage without increasing the overall pitchwise spacing or causing interference between adjacent buttons. The undercut creates additional coverage area that would be impossible with a conventional cylindrical button of the same outer diameter.
Solution Approach 2:
The biconic button with undercut portion effectively nests beneath adjacent buttons in the pitchwise direction. The undercut creates a recessed area that allows buttons to be positioned closer together while maintaining adequate clearance at the outer diameter, thereby reducing endwall gaps without requiring larger button diameters that would cause overlap.
2Loss of energy
If larger button diameters are used to reduce endwall gaps, then endwall coverage improves, but buttons overlap and cannot be fitted together
Solution Approach 1:
The biconic configuration with undercut allows the button to utilize the radial-inward dimension more effectively. By extending the button body inwardly beneath adjacent buttons rather than outwardly to increase diameter, the design achieves greater endwall coverage while maintaining compatibility with the fixed pitchwise spacing between vanes.
Solution Approach 2:
The undercut geometry is designed to anticipate and accommodate the positioning constraints of adjacent buttons. By pre-shaping the button with the undercut portion, the design ensures that when buttons are assembled in circumferential rows, they fit together without interference while still providing maximum endwall coverage within the available space.
3Area of stationary object
If flats or arched cuts are added to buttons to allow larger diameters, then endwall coverage improves, but large cavities are created between buttons
Solution Approach 1:
The biconic button applies the undercut modification locally at the region where endwall coverage is most needed, rather than using global modifications like flats or arched cuts that affect the entire button periphery. This localized approach increases endwall coverage without creating large cavities between buttons, as the undercut is positioned to fill specific gap regions while maintaining button integrity.
4Volume of moving object
If cylindrical buttons with maximum diameter are used in HPC VSVs with sloped inner flowpaths, then button size is maximized, but interference at the bottom of the button limits further size increase
Solution Approach 1:
The biconic configuration changes the button geometry from a simple cylinder to a more complex shape with an undercut portion. This dimensional change allows the button to achieve greater effective volume and endwall coverage by utilizing the radial-inward space beneath adjacent buttons, while the sloped surfaces of the biconic design reduce interference with the sloped inner flowpaths of HPC VSVs.
Solution Approach 2:
The biconic button design with its sloped surfaces adapts dynamically to the varying flowpath geometry in HPC VSVs. The undercut portion allows the button to maintain optimal size across different vane angle settings and positions, reducing interference with the sloped inner flowpaths while maximizing endwall coverage throughout the operational range.
Data Source
AI summary
A variable stator vane includes airfoil mounted to a button centered about a rotational axis and having cylindrical portion supporting airfoil and a button undercut extending away from cylindrical portion and radially inwardly from circumference of cylindrical portion. Conical portion of button circumscribed about conical axis of revolution extends away from cylindrical portion. Conical axis of revolution may be tilted with respect to and may intersect rotational axis. Airfoil may include airfoil overhang extending radially outwardly beyond circular trailing edge of button. Variable stator vane may include airfoil disposed between spaced apart outer and inner buttons centered about a rotational axis, inner button having a cylindrical portion supporting airfoil and circumscribed about rotational axis, and button undercut extending away from cylindrical portion and radially inwardly from a circumference of cylindrical portion with respect to rotational axis. Outer and inner spindles extend from outer and inner buttons and airfoil.