Turbomachine Blisk Recess Reduces Blade Base Stress
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Solution Overview
Problem
In turbojet engines with single-piece blisks, the ingestion of a foreign body leads to significant mechanical stress concentration at the base of the blades, increasing the risk of blade degradation or tearing due to the increased stiffness at the hub connection, which is not effectively managed by existing designs.
Innovation Solution
The design of the single-piece blisk features a hub with an external peripheral face that is tapered and offset, reducing the anchorage length of the blades, allowing for increased flexibility about the rotation and radial axes, thereby reducing stress concentrations by allowing energy absorption from shocks without altering the blade geometry relative to fluid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the single-piece blisk structure is used to connect blades to the hub, then the structural integrity and manufacturing efficiency are improved, but the stress concentration at the blade base increases during foreign body ingestion
Solution Approach 1:
The patent applies local quality by creating a recess in the hub that specifically modifies the local geometry at the blade-root connection zone. This recess reduces the stiffness locally at the connection point while maintaining the overall single-piece blisk structure, thereby reducing stress concentration during foreign body ingestion without compromising manufacturing efficiency
Solution Approach 2:
The patent changes the geometric parameter of the hub by introducing a recess that reduces the anchorage length of the blades. This parameter change (reducing the embedded length of blades in the hub) decreases the stiffness at the blade base, allowing better stress distribution and reduced stress concentration during impact events while maintaining the integrated blisk manufacturing approach
2Strength
If the blade anchorage length in the hub is increased to improve connection strength, then the structural strength is improved, but the flexibility of the blade decreases
Solution Approach 1:
The recess creates a local geometric modification that differentiates the connection zone from the rest of the hub structure. This local quality change allows the blade base to have reduced stiffness and increased flexibility while the broader hub structure maintains overall strength, resolving the contradiction between connection strength and blade flexibility
Solution Approach 2:
The patent enables dynamic behavior by allowing the blade to have variable flexibility along its length. The recessed region creates a gradient in stiffness, allowing the blade to be stiffer near the leading edge for structural integrity while being more flexible at the base for shock absorption, thus achieving both strength and adaptability
Data Source
AI summary
The invention relates to a single-piece fan blisk (14) for a turbojet, this blisk (14) comprising a hub (16) with a general shape of revolution about a rotation axis (AX) and comprising an external peripheral face (18) of revolution extending radially towards the rotation axis at an upstream face (19) and a downstream face both of which are in the form of rings. This hub (16) supports radially oriented blades (17) at its external peripheral face (18), each comprising a base through which it is connected to this external peripheral face (18), each blade (17) having a leading edge (22) and a trailing edge (23) that are radially oriented. The spacing between the upstream face (19) and the downstream face of the hub (16) along the rotation axis (AX) is less than the distance separating the leading edge (22) from the trailing edge (23) of each blade.