Inner Bypass Duct Wall Attachment for Thermal Stress Reduction
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Solution Overview
Problem
Turbofan engines face cracking issues in core cases and brackets due to thermal expansion mismatch between the inner bypass duct wall and engine core cases, leading to stress and maintenance challenges.
Innovation Solution
A mounting arrangement with a rigid connection at the front end and a flexible connection at the rear end of the inner bypass duct wall, allowing thermal growth and contraction relative to the core case, using a combination of bolted connections and flexible links to maintain concentricity and reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the inner bypass duct wall is rigidly attached to the core case at both ends, then structural stability is improved, but thermal stress and cracking increase
Solution Approach 1:
The mounting arrangement divides the connection into two distinct segments: a rigid connection at the front end and a flexible connection at the rear end. This segmentation allows each end to serve its specific function - the front end maintains structural stability while the rear end accommodates thermal growth, thereby preventing cracking in the core case and brackets.
Solution Approach 2:
Different connection types are applied to different locations of the inner bypass duct wall based on local thermal and structural requirements. The front end uses a rigid connection where structural stability is critical, while the rear end uses a flexible connection where thermal growth accommodation is needed. This local differentiation resolves the contradiction between stability and cracking resistance.
2Strength
If multiple steel brackets are used to attach the inner bypass duct wall, then structural support is improved, but device complexity and assembly difficulty increase
Solution Approach 1:
The mounting arrangement merges the functions of multiple separate steel brackets into two integrated mounting structures - one rigid mounting at the front end and one flexible mounting at the rear end. Each mounting structure combines the support function of multiple brackets into a single unified component, thereby reducing the total number of brackets while maintaining structural support.
Solution Approach 2:
The rigid and flexible mountings serve multiple functions simultaneously: they provide structural support, accommodate thermal growth, and simplify assembly. The flexible mounting, for example, acts as both a support structure and a thermal expansion joint, eliminating the need for separate brackets for each function.
3Stress or pressure
If the inner bypass duct wall is freely movable relative to the core case, then thermal stress is reduced, but concentricity and positioning accuracy deteriorate
Solution Approach 1:
The connection is segmented into rigid and flexible portions, allowing the inner bypass duct wall to move freely at the rear end to reduce thermal stress while maintaining rigid connection at the front end to preserve concentricity. This segmentation enables simultaneous achievement of stress reduction and positioning accuracy.
Solution Approach 2:
The flexible mounting acts as an intermediary element between the inner bypass duct wall and the core case at the rear end. It mediates the thermal growth by allowing controlled movement while maintaining the overall concentric alignment, thereby reducing stress without sacrificing positioning accuracy.
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 solution reduces stress on brackets and core cases, minimizes cracking, decreases maintenance costs, and simplifies assembly by eliminating multiple steel brackets and reducing fastener count, while maintaining concentricity and allowing thermal expansion of engine core components.
Implementation Method 1
the flexible connection allowing the rear end portion of the core case to thermally grow and contract relative to the radially inner bypass duct wall
Data Source
AI summary
A bypass duct of a gas turbine engine has an inner bypass duct wall having a front end portion which is rigidly mounted to an engine core case and a rear end portion which is flexibly mounted to the core case. The flexible mounting between the rear portion of the inner bypass duct wall and the core case allows hot engine areas of the core case to thermally grow and contract relative to the inner bypass duct wall without imposing additional loads on the inner bypass duct wall.