Labyrinth Seal Abradable Structure to Prevent Rotor Locking
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Solution Overview
Problem
Labyrinth seals in turbomachines, particularly in aircraft engines, face challenges in reducing leakage rates and preventing rotor locking due to differential thermal and mechanical expansions, which can lead to blocking issues during engine restarts.
Innovation Solution
The abradable structure in the labyrinth seal is designed with regions of varying wear resistance, where the most resistant areas face the rotor at cruising speed and less resistant areas face the rotor during engine restarts, utilizing an additive manufacturing technique to create a single-piece structure with obliquely oriented partitions, reducing the formation of hard points and preventing rotor locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the abradable structure uses a honeycomb design with uniform cell distribution, then the seal provides consistent wear resistance during normal operation, but it creates hard points that can cause rotor locking during engine restarts
Solution Approach 1:
The patent applies local quality by creating different cell densities in different axial regions of the abradable structure. The upstream region (facing the rotor at cruising speed) has higher cell density for wear resistance, while the downstream region has lower cell density to prevent rotor locking during restarts. This spatial variation in structural properties resolves the contradiction between needing hard wear-resistant surfaces and avoiding harmful locking effects.
Solution Approach 2:
The abradable structure is segmented into multiple axial regions with progressively different cell densities. This segmentation allows each region to perform its specific function: the upstream regions provide wear resistance during normal operation, while downstream regions provide compliance during transient conditions. The segmentation strategy enables the structure to handle different operational phases with appropriate local properties.
2Strength
If the abradable material is made harder to increase wear resistance, then the seal durability improves, but the risk of rotor blocking during engine restarts increases
Solution Approach 1:
Rather than making the entire abradable structure uniformly hard, the patent applies local quality by varying the cell density locally. Harder, denser cell structures are placed only where wear resistance is needed (upstream regions), while softer, more compliant regions are placed downstream where rotor locking risks occur during restarts. This resolves the contradiction between strength and safety.
Solution Approach 2:
The abradable structure functions as a composite material system with regions of different effective mechanical properties. The progressive cell density variation creates a gradient composite structure that combines hard wear-resistant zones with soft compliant zones, allowing the system to achieve both wear resistance and rotor safety simultaneously.
3Reliability
If the honeycomb cells are oriented with partitions perpendicular to the rotor motion, then the structure provides maximum wear resistance, but it increases the likelihood of rotor locking during transient conditions
Solution Approach 1:
The patent applies local quality by varying cell orientation and density locally across different axial regions. Upstream regions have cells oriented for maximum wear resistance, while downstream regions have different orientations and lower densities that reduce locking risks. This spatial differentiation resolves the contradiction between wear resistance and blocking prevention.
Solution Approach 2:
The abradable structure exhibits dynamic behavior through its progressive cell density design. During normal cruising operation, the dense upstream cells provide rigid wear resistance. During transient conditions like engine restarts, the less dense downstream cells provide compliance and flexibility, allowing the structure to adapt its mechanical response to different operational phases.
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 effectively reduces the risk of rotor blocking during engine restarts while maintaining efficient gas leakage management, ensuring safety and performance by adapting wear resistance to different operational phases.
Implementation Method 1
differential thermal or mechanical expansions (due to heating or centrifugal forces), occurring under circumstances such as transient regimes, temporarily bring the abradable and the ridge crests into contact
Implementation Method 2
differential thermal or mechanical expansions (due to heating or centrifugal forces), occurring under circumstances such as transient regimes, temporarily bring the abradable and the ridge crests into contact
Implementation Method 3
The leakage flow of gases around the rotor 1 has its flow rate reduced by the section restrictions imposed on it to bypass the wipers 4 and 5
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An abradable structure (36) is provided, with regions (44, 45, 46) with lower resistance to wearing produced by labyrinth seal lips (4, 5), at specific points in the axial direction of the turbomachine, where lip interference could cause the rotor to block up, such as after a temporary shutdown of the turbomachine. These regions may be produced by local weakening (38) or by the abradable material having a structure that is less dense. Application, for example, to turbomachine turbines.