Unitary Mid-Turbine Frame Casting for Thermal Stress Management
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Solution Overview
Problem
Gas turbine mid-turbine frames are subject to thermal stresses from combustion gases, which can reduce operational life, and existing designs with bolted joints face unique challenges in load transfer and cooling, requiring innovative structural and cooling solutions.
Innovation Solution
A unitary, one-piece cast mid-turbine frame with a specific ratio of exit outer diameter to axial length greater than 3.0 to 1, featuring tie rods extending through vanes secured to inner and outer cases, allowing the frame to float and incorporate active cooling passages for efficient heat management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a bolted joint is used to connect the MTF to the outer case structure, then the load transfer capability is improved, but the structural complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the MTF with the inner case structure into a unitary one-piece cast component, eliminating the need for separate bolted joints while maintaining load transfer capability through the integrated structure. This combining approach reduces structural complexity while preserving strength.
Solution Approach 2:
The patent segments the load transfer function by providing dedicated load transfer features (such as reinforced vane roots and integrated tie rod mounting points) within the unitary structure, allowing localized strength enhancement without increasing overall structural complexity.
2Reliability
If actively cooled vanes with serpentine cooling passages are implemented, then the thermal stress resistance is improved, but the device complexity and cooling fluid requirements increase
Solution Approach 1:
The cooling passages are merged directly into the vane structure during the one-piece casting process, integrating the cooling function into the structural component itself. This eliminates separate cooling system components and reduces overall device complexity while maintaining thermal stress resistance.
Solution Approach 2:
The patent utilizes internal cooling passages (effectively creating a controlled porous structure) within the vanes to allow cooling fluid flow, enabling heat dissipation without adding external cooling components. The cast structure naturally accommodates these internal fluid pathways.
3Strength
If the MTF uses a shallow cone angle of 15°, then the load transfer efficiency through the MTF is improved, but the axial length increases reducing compactness
Solution Approach 1:
The patent optimizes the cone angle parameter of the MTF to balance load transfer efficiency with axial length constraints. By adjusting this geometric parameter, the design achieves adequate load transfer capability while maintaining a compact axial footprint suitable for modern engine configurations.
Solution Approach 2:
The use of one-piece cast construction allows for optimized material distribution and density variations within the MTF structure, enabling efficient load transfer with reduced axial length compared to traditional multi-component designs.
4Ease of manufacture
If a unitary one-piece cast structure is used for the MTF, then the structural integrity and manufacturing simplicity are improved, but the adaptability to different cooling approaches and load paths is reduced
Solution Approach 1:
The unitary MTF structure is designed with multi-functional features that can accommodate different cooling approaches and load path configurations within the same basic structure. The integrated design includes versatile mounting points and cooling passage options that can be adapted to various engine requirements without requiring fundamental design changes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the structural integrity and cooling efficiency of the mid-turbine frame, improving its operational life by effectively managing thermal stresses and load transfer, while maintaining a compact design suitable for gas turbine engines.
Implementation Method 1
actively cooled vanes that include serpentine cooling passages provided cooling fluid from a bleed source
Implementation Method 2
The MTF is subject to thermal stresses from combustion gases along the core gas path
Data Source
AI summary
A gas turbine engine includes a core flow path that extends axially about an engine axis. A turbine section is arranged in the core flow path. A mid-turbine frame includes multiple circumferentially spaced vanes that extend radially between and interconnect inner and outer flow path surfaces that define a portion of the core flow path. The vanes and inner and outer flow path surfaces are provided by a unitary, one-piece cast structure. The inner flow path surface provides inlet and exit inner diameters relative to the engine axis. The outer flow path surface provides inlet and exit outer diameters relative to the engine axis. The inner flow path surface extends an axial length from the inlet inner diameter to the exit inner diameter. A ratio of the exit outer diameter to the axial length is greater than 3.0 to 1.