Asymmetric Trunnion Alignment for Variable Stator Vanes
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Solution Overview
Problem
The assembly process of variable stator vanes in gas turbine engines often results in misalignment due to the interference fit between the D-shaped trunnion seat and lever arm, which can lead to aerodynamic distortion and reduced compressor performance, especially in compact engine designs where additional length for longer retention nuts is not feasible.
Innovation Solution
The design incorporates a trunnion seat with parallel seating flats and a threaded stem featuring a flat and arcuate alignment surface, along with a complementary mounting hole, to facilitate self-alignment and prevent misorientation of the lever arm during assembly, ensuring proper engagement and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a D-shaped seat and complementary D-shaped mounting hole are used to eliminate misalignment, then alignment precision should be improved, but misalignment still occurs during assembly due to interference fit
Solution Approach 1:
The patent applies asymmetry by providing a flat alignment surface on the threaded stem that corresponds to a flat surface on the trunnion seat, while other portions have arcuate surfaces. This asymmetric geometry ensures that the lever arm can only be installed in the correct orientation, preventing misalignment during assembly while maintaining the interference fit for secure attachment.
2Manufacturing precision
If retention nuts of sufficient length are used to prevent misalignment by requiring lever arm seating first, then alignment precision is improved, but the threaded stem requires additional length which is not feasible in compact engine designs
Solution Approach 1:
The asymmetric alignment surfaces (flat surface on threaded stem matching flat surface on trunnion seat) enable correct orientation to be established during the interference fit process itself, eliminating the need for extended retention nut length. The geometry ensures proper alignment is achieved naturally as the lever arm is installed, without requiring additional components or increased length.
Solution Approach 2:
The alignment surfaces perform the alignment function preliminarily during the installation process, before the retention nut is fully tightened. The flat alignment surface guides the lever arm into correct orientation as it approaches the trunnion seat, ensuring proper alignment is established before final securing, thus eliminating the need for longer retention nuts.
3Ease of operation
If the lever arm is secured to the trunnion seat without confirming correct orientation, then assembly process is simplified, but misalignment occurs leading to aerodynamic distortion
Solution Approach 1:
The asymmetric alignment surfaces provide a self-aligning mechanism that guides the lever arm into the correct orientation during assembly. The flat surface on the threaded stem must match the flat surface on the trunnion seat, which naturally orients the lever arm correctly as it is installed, eliminating the need for separate orientation confirmation steps while ensuring precise alignment.
Solution Approach 2:
The alignment surfaces enable the assembly process to self-correct and self-align during installation. The geometric constraint of the flat alignment surfaces automatically orients the lever arm correctly as it approaches the trunnion seat, allowing the system to self-align without requiring additional verification steps or complex assembly procedures.
Data Source
AI summary
A variable stator vane includes an airfoil having a first end, a second end, and a longitudinal axis connecting the first end with the second end. The variable stator vane further includes a first trunnion disposed along the longitudinal axis at the airfoil first end. The first trunnion includes a trunnion seat extending integrally from a distal end of the trunnion opposite the airfoil. The trunnion seat includes first and second parallel seating flats opposing each other about the longitudinal axis. The variable stator vane further includes a threaded stem extending integrally from the trunnion seat and coaxial with the trunnion about the longitudinal axis. The threaded stem includes a flat first alignment surface coextensive with the first parallel seating flat in the longitudinal direction, and an arcuate second alignment surface aligning with the second parallel seating flat in the longitudinal direction.