Airfoil Connector Managing Thermal Growth Between Shell and Spar
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Solution Overview
Problem
Spar-and-shell airfoil configurations in gas turbine engines face high thermal stress due to temperature differences between the shell and spar, leading to potential cracking of ribs that connect the shell to the spar, especially under high cooling air pressure.
Innovation Solution
The airfoil design incorporates a connector system with engageable portions and a link that allows for axial thermal growth between the shell and spar, minimizing stress by enabling relative movement and utilizing trailing edge flow to reduce dedicated cooling needs, while also featuring axial and radial flow paths and heat transfer augmentation features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the shell is rigidly secured to the spar with ribs, then the thin shell wall can be held to the spar under high cooling air pressure, but high thermal stress loads are produced on the ribs due to temperature differences between the shell and spar
Solution Approach 1:
The connector is designed with a pinned connection that allows rotational movement, transforming the rigid static connection into a dynamic flexible connection. This enables the connector to accommodate thermal expansion and contraction of the shell relative to the spar, reducing thermal stress while maintaining structural integrity under pressure loads
Solution Approach 2:
The connector geometry (lemniscate shape) is specifically designed to change its effective length and orientation in response to thermal growth, allowing the connection to adapt to temperature-induced dimensional changes between the shell and spar without generating excessive stress
2Force
If high cooling air pressure is used between the shell and spar, then the thin shell wall can be held to the spar, but the thermal stress loads on the ribs increase
Solution Approach 1:
The pinned connector allows the shell-spar connection to flex and rotate, accommodating the forces generated by high-pressure cooling air while preventing these forces from being transmitted as thermal stress to the ribs. The flexible connection absorbs mechanical loads separately from thermal effects
3Strength
If a number of ribs are used to hold the thin shell wall to the spar, then the shell can be secured under high cooling air pressure, but the complexity of the structure increases
Solution Approach 1:
The traditional rib structure is completely removed and replaced by a continuous connector system that integrates the support function into the shell-spar connection itself. This eliminates the need for separate ribs while maintaining the ability to support the shell under high cooling air pressure
Solution Approach 2:
The connector serves multiple functions simultaneously: it provides structural support for the thin shell wall, accommodates thermal growth, and allows for pressure differential loading. This multi-functional design replaces what would traditionally require multiple separate components
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
This design reduces thermal stress on the ribs and minimizes the amount of dedicated cooling required, enhancing the efficiency and effectiveness of the cooling scheme while allowing for the use of both nickel and ceramic matrix composite materials.
Implementation Method 1
an axial flow path through the outer cavity... impinging air is configured to flow from the inner cavity to the outer cavity... and flow axially aftward through the axial flow path of the outer cavity
Implementation Method 2
large temperature differences (e.g., high temperature at the shell, relatively low temperature at the spar)... the temperature difference will produce high thermal stress loads on the ribs
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
The airfoil (300) include a shell (302) having a first channel (322) and a first engagement element (324) arranged along the first channel and a spar (204) having a second channel (330) and a second engagement element (332) arranged along the second channel and the spar defines an inner cavity (318). A connector (306) is configured to be installed between and connect the shell and the spar to allow for thermal growth of the shell relative to the spar. The connector has first and second engageable portions (340) connected by a link (446). The first engageable portion is configured to engage with the shell and the second engageable portion is configured to engage with the spar. When assembled, an outer cavity (320) is formed between the spar and the shell.