Rotating Labyrinth Seal Crack Prevention via Offset Notches

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Solution Overview

Problem

Rotating labyrinth seals in gas turbine engines are prone to cracking due to rub damage, which can propagate into the torque-carrying load path, leading to potential turbine overspeed, disc burst, and increased economic costs for inspections and coatings.

Innovation Solution

The introduction of a separate component within the seal geometry that separates the seals from the load transmitting structures, and the use of notches in the seal fins to reduce hoop stress and prevent crack propagation, along with offsetting notches on adjacent fins to maintain seal effectiveness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the seal teeth are made thin to thermally isolate them from the base, then thermal isolation is improved, but susceptibility to handling damage and crack formation increases

Engineering Contradiction:

Improvethermal isolationVSAvoidsusceptibility to crack formation

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The seal structure is divided into separate components: the seal teeth are made as a distinct element that can be attached to the base structure. This segmentation allows the thin seal teeth to be thermally isolated while the base provides structural support, reducing the risk of cracks propagating into the load path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The seal teeth are extracted as a separate component from the base structure, allowing them to be independently designed with optimal thickness for thermal isolation without compromising the structural integrity of the base. The separate attachment method ensures cracks remain localized to the seal teeth.

Inventive Principle:

Principle #2Taking out (Extraction)

2Strength

If the seal teeth are integrated into the shaft or disc structure, then structural strength is improved, but crack propagation into the load path becomes possible

Engineering Contradiction:

Improvestructural strengthVSAvoidrisk of catastrophic failure

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The seal assembly is segmented into the base structure and the seal teeth, which are attached but not integrally connected. This allows the base to carry structural loads while the seal teeth can be replaced if damaged, preventing crack propagation into the load path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The seal teeth are taken out as a removable component from the integral structure. By making them detachable, the design allows damaged seal teeth to be replaced without compromising the shaft or disc, isolating potential cracks to non-critical components.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If conventional seal designs are used, then manufacturing simplicity is maintained, but rub damage and crack formation occur

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidrub damage resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The seal is segmented into a base and attachable seal teeth, allowing the teeth to be pre-treated with protective coatings or materials resistant to rub damage. This modular approach maintains manufacturing simplicity while improving reliability through specialized material selection.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS10450963B2Shaft seal crack obviation

Publication Date: 2019.10.22 ROLLS ROYCE CORP

AI summary

A rotating labyrinth seal especially useful for effecting sealing between two plenums in aircraft gas turbine engines comprising a base and a plurality of radially-directed seal teeth rings extending circumferentially around the outer peripheral surface of the base. The fins in the rotating seal each having a discontinuity that reduces hoop stress on the outer radial surface. The discontinuities in each fin are offset from the discontinuities in the adjacent fins.