CMC Turbine Vane Spar Segmentation for Stress Reduction
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Solution Overview
Problem
Ceramic matrix composite (CMC) turbine engine vanes face high mechanical stress due to pressure differentials, which is challenging to manage without increasing thermal stress, and manufacturing integral ribs for CMCs is difficult, limiting the feasibility of stress reduction methods like spanwise tensile ribs or increasing shell thickness.
Innovation Solution
A vane design featuring a thin-walled CMC shell with a metal alloy spar and multiple chambers within the shell, allowing differential internal pressure distribution through seals and chambers to reduce mechanical stress, while maintaining optimal aerodynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the shell thickness is increased to improve mechanical strength, then the resistance to mechanical loading is improved, but the thermal stress increases
Solution Approach 1:
The spar is divided into multiple chambers (first chamber along suction side, second chamber along pressure side) that can be independently pressurized. This segmentation allows differential pressure management to reduce mechanical stress on the shell while maintaining structural integrity, avoiding the need to increase overall shell thickness which would raise thermal stress.
Solution Approach 2:
Different internal pressures are applied to different regions of the spar (first chamber vs. second chamber) based on local stress requirements. The suction side chamber and pressure side chamber can have different pressure levels to optimize stress distribution in specific areas without uniformly thickening the entire shell.
2Strength
If spanwise tensile ribs or webs are added to strengthen the shell, then the pressure loading resistance is improved, but the manufacturing complexity and thermal stress concentration increase
Solution Approach 1:
The spar structure serves multiple functions simultaneously: it provides structural support, enables differential pressure management through its chambers, and reduces mechanical stress on the shell. This multi-functionality eliminates the need for separate tensile ribs while achieving pressure loading resistance through the integrated chamber design.
Solution Approach 2:
Instead of adding structural features like ribs, the solution changes the pressure parameters within the spar chambers. By controlling the internal pressure distribution between the first and second chambers, the system achieves mechanical stress reduction without adding complex structural elements that would be difficult to manufacture in CMC.
3Stress or pressure
If the bend radius at the leading edge is increased to reduce stress concentration, then the stress is reduced, but the aerodynamic performance deteriorates
Solution Approach 1:
The differential pressure system acts as an intermediary mechanism that reduces mechanical stress on the shell without requiring changes to the external aerodynamic profile. By managing internal pressure distribution through the spar chambers, the system protects the optimized airfoil geometry from stress concentration issues.
Data Source
AI summary
A vane has an airfoil shell and a spar within the shell. The vane has an outboard shroud at an outboard end of the shell and an inboard platform at an inboard end of the shell. The spar has a first chamber essentially along the suction side and a second chamber along the pressure side opposite the first chamber.