Turbine Vane CMC Heat Shield Load Transfer
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Solution Overview
Problem
Ceramic-matrix composite (CMC) materials in gas turbine engines face challenges in managing tensile stresses at the leading edge of turbine vanes due to aero-load transfer from the vane to the outer endwall, which can lead to design limitations in load transfer efficiency.
Innovation Solution
A turbine vane assembly design incorporating a metallic vane support with a load transfer flange and a gas path heat shield made from ceramic matrix composite materials, where the suction side of the heat shield is thickened to engage the load transfer flange, providing an aero-load transfer interface that carries circumferentially directed aerodynamic loads and relieves tensile stresses by converting them into compressive forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If CMC material is used for the gas path heat shield, then weight is reduced and turbine entry temperatures are increased, but tensile stresses develop at the leading edge where the vane intersects the outer endwall
Solution Approach 1:
The endwall is designed with non-uniform thickness, featuring a thickened suction side portion that provides additional load-bearing capacity specifically at the leading edge region where tensile stresses occur. This localized thickening allows the CMC heat shield to maintain its weight advantage while providing enhanced structural support where needed.
Solution Approach 2:
The suction side portion of the endwall is intentionally made thicker than the pressure side portion, creating an asymmetric structure. This asymmetry is designed to counteract the asymmetric stress distribution in the CMC heat shield, particularly the tensile stresses on the suction side at the leading edge, by providing additional material strength where the stresses are highest.
2Stress or pressure
If a fillet is used to manage stress magnitude at the leading edge, then stress concentration is reduced, but the design complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of applying a fillet along the entire leading edge perimeter, the thickening is applied selectively to the suction side portion of the endwall. This localized approach provides the necessary stress management while avoiding the complexity of implementing fillets on both the pressure and suction sides, thereby reducing manufacturing difficulty.
3Strength
If the suction side portion of the endwall is thickened to engage the load transfer flange, then aerodynamic loads are effectively transferred to the vane support, but the volume and weight of the heat shield increase
Solution Approach 1:
The endwall thickening is confined to the suction side portion only, rather than uniformly thickening the entire endwall. This localized thickening provides the necessary load transfer capability for engaging the load transfer flange while minimizing the additional volume and weight compared to a uniform thickening approach.
Data Source
AI summary
A vane assembly for a gas turbine engine is provided having an outer casing and an inner casing radially spaced apart from the outer casing. An airfoil extends radially between the outer casing and the inner casing. The airfoil includes a spar having an outer endwall positioned adjacent the outer casing and an inner endwall positioned adjacent the inner casing. A pressure side and a suction side extend between the inner endwall and the outer endwall. A ceramic matrix composite cover has a pressure side extending along the pressure side of the spar and a suction side extending along the suction side of the spar.