Gas Turbine Rotor Containment via Interference Fit
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Solution Overview
Problem
In multi-shaft gas turbine engines, the design faces challenges in containing rotor stability during foreign object ingestion or blade loss events, particularly due to close inter-shaft clearances and the complication of a full-length tie-shaft, which can lead to shaft separation and subsequent deceleration issues, requiring effective containment mechanisms to prevent rotor separation and manage separating loads.
Innovation Solution
The design incorporates a spool assembly with a region of enlarged diameter on the second shaft that engages the first shaft in an interference fit when axially moved, maintaining the compressor and turbine rotors as a single mass and utilizing a bell-shaped support for centering and energy dissipation, along with crushable features to absorb kinetic energy and prevent rotor separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If close inter-shaft clearances are used in concentric multi-shaft designs, then device complexity is reduced and efficiency is improved, but rotor stability deteriorates during foreign object ingestion or blade loss events
Solution Approach 1:
The shaft system is segmented into discrete sections with a shearable connection between them. The first shaft (compressor-turbine) and second shaft (fan-low pressure turbine) are separated by a defined interface that allows controlled separation. This segmentation enables the shafts to remain stable during normal operation with close clearances, but allows independent movement during abnormal events to maintain stability.
Solution Approach 2:
The containment structure is pre-configured with clearance gaps and shearable connections at predetermined locations. These preliminary arrangements ensure that when abnormal forces occur, the shafts can separate along predefined paths without chaotic movement, maintaining stability throughout the separation process.
2Strength
If a full length tie-shaft is used to join compressor and turbine rotor sections, then structural integrity is improved, but containment design complexity increases
Solution Approach 1:
The tie-shaft connection is divided into a shearable section that separates the compressor and turbine rotor sections. This segmented approach maintains structural integrity during normal operation while enabling controlled separation during abnormal events, reducing containment complexity by eliminating the need to contain a fully integrated rigid structure.
Solution Approach 2:
The shearable connection feature is extracted from the tie-shaft design, allowing the tie-shaft to be removed or separated under specific conditions. This extraction enables the system to transition from a rigid integrated structure to separated sections, simplifying containment requirements while maintaining strength during normal operation.
3Stability of the object's composition
If shaft separation is allowed during blade loss events, then rotor stability is improved, but the number of rotating masses to contain increases
Solution Approach 1:
The containment structure merges the first and second shafts into a single integrated containment envelope. By designing the containment to accommodate both shafts together rather than as separate contained entities, the patent reduces the effective number of rotating masses that must be contained, even though physical separation occurs during abnormal events.
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 configuration effectively impedes rotor separation, maintains rotor stability, and provides a mechanical braking feature to prevent turbine overspeed, ensuring containment and energy absorption during shaft separation events.
Implementation Method 1
the region of enlarged diameter having a diameter greater than an inner diameter of at least a portion of the forward end of the first shaft to cause the region of enlarged diameter of the second shaft to axially engage the first shaft in interference
Implementation Method 2
utilizing a bell-shaped support for centering and energy dissipation
Implementation Method 3
crushable features to absorb kinetic energy and prevent rotor separation
Data Source
AI summary
A gas turbine engine has a spool including compressor and turbine rotors connected by a first shaft. The first shaft extends concentrically around a second shaft. The first shaft forward end has a portion with an inner diameter of close tolerance with the second shaft. The second shaft has a region of enlarged diameter located axially aft of the compressor rotor but axially forward of the forward end of the first shaft. The region of enlarged diameter has a diameter greater than the inner diameter of the forward end portion of the first shaft to cause the region of enlarged diameter of the second shaft to engage the first shaft in interference in the event that the second shaft is moved axially aft relative to the first shaft more than a pre-selected axial distance.