Compressor Variable Vane Projections for Clearance Control
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Solution Overview
Problem
Variable vanes in gas turbine engine compressors experience increased vane tip losses due to varying clearance gaps as they pivot, affecting aerodynamic performance and compressor efficiency.
Innovation Solution
The introduction of projections on the inner and outer shrouds with angled planar surfaces that maintain a constant radial clearance gap between the vane airfoil and the shroud, minimizing turbulence and aerodynamic losses throughout the vane's pivot arc.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable vanes pivot about radially extending axes to optimize compressor efficiency and operability, then the angle of the vane airfoil can be adjusted to match rotor blade angle, but the clearance gap between the vane airfoil and surrounding shrouds varies, leading to greater vane tip losses
Solution Approach 1:
The shroud surface is segmented into multiple planar surfaces (first planar surface, second planar surface, third planar surface) that are angled relative to each other. These segmented surfaces work together to maintain constant clearance gap as the vane pivots, with each surface addressing a specific angular position range of the vane airfoil.
Solution Approach 2:
Different portions of the shroud have different geometric configurations tailored to local requirements. The first planar surface is positioned to maintain clearance at one angular position, the second planar surface at another angular position, and the third planar surface addresses the trailing edge region. This local customization of geometry ensures constant clearance gap throughout the entire pivot arc.
2Productivity
If variable vanes are used to provide closer incidence match between air flow and rotor blade angle, then compressor efficiency is improved, but the varying clearance gap negatively affects aerodynamic performance
Solution Approach 1:
The shroud geometry is designed to dynamically adapt to the changing position of the pivoting vane airfoil. The multiple angled planar surfaces are configured so that as the vane rotates through its pivot arc, different surfaces engage to maintain constant clearance gap, making the clearance system dynamic rather than static.
Solution Approach 2:
The multiple planar surfaces act as intermediary elements between the pivoting vane airfoil and the stationary shroud structure. These surfaces mediate the clearance gap maintenance function, ensuring that the varying angular position of the vane does not result in varying clearance, thereby protecting aerodynamic performance while allowing vane rotation for efficiency optimization.
Data Source
AI summary
A variable vane assembly for a gas turbine engine compressor and method of manufacturing same is described. A plurality of projections on the inner and/or outer shroud protrude into the annular gas path, each projection being at least partially circumferentially disposed between two variable vanes and located adjacent the overhang portion thereof. The projections have an angled planar surface that is substantially parallel to a plane defined by a terminal edge of the overhang portion of the variable vanes when pivoted through a vane pivot arc.