Split Sealing Mechanism for Turbomachine Platforms
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Solution Overview
Problem
Existing rotary assemblies for turbomachines face challenges in effectively sealing inter-blade cavities, leading to gas leakage and heating of the disc, particularly when using Ceramic Matrix Composite (C.M.C.) blades, due to high centrifugal loads and differential expansions causing stress and potential clearances.
Innovation Solution
A split sealing mechanism where the outer part is retained by the platforms and the inner part can be held by the disc or another rotating element, allowing for relative radial displacements to reduce stress and maintain axial sealing, with the external part supporting centrifugal forces and the internal part being axially locked to ensure effective sealing without generating excessive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic annular ring is used to seal the inter-blade cavities, then the sealing effectiveness is improved, but the centrifugal load on the platforms increases significantly
Solution Approach 1:
The sealing ring is divided into two separate parts: an internal part held by the disc and an external part held by the platforms. This segmentation allows the sealing function to be maintained while distributing the centrifugal loads to different structural elements, with only the external part bearing load from the platforms.
Solution Approach 2:
The invention introduces an intermediary arrangement where the internal part of the sealing ring is held by the disc through a hooked annular portion engaging with projecting portions on the disc, rather than having the platforms directly support the entire ring. This intermediary support structure reduces the burden on the platforms.
2Weight of moving object
If CMC blades are used, then the weight is reduced and temperature resistance is improved, but the platforms cannot support the centrifugal load and differential expansion issues arise
Solution Approach 1:
By segmenting the sealing ring into two parts with different support structures, the invention enables the use of lighter CMC blade materials while maintaining sufficient platform load bearing capacity. The internal part is supported by the disc, reducing the burden on platforms that would otherwise need to support the full centrifugal load of CMC blades.
Solution Approach 2:
The invention accommodates differential thermal expansion between CMC blades and metallic components by allowing relative radial movement between the two parts of the sealing ring. This parameter change in the sealing mechanism's flexibility enables compatibility with CMC materials that have different thermal expansion characteristics.
3Reliability
If walls are extended radially inward to seal the inter-blade cavities, then the sealing is improved, but multiple gaps between adjacent walls allow gas circulation
Solution Approach 1:
The invention merges the sealing function into a continuous annular structure (the sealing ring) that spans across all inter-blade cavities. This single continuous sealing element eliminates the multiple discrete gaps that would exist between separate radial walls, providing comprehensive sealing without the complexity of multiple separate sealing components.
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 the load on the platforms, minimizes fatigue, and maintains effective sealing equivalent to a single annular element, allowing for the use of C.M.C. blades while preventing gas leakage and ensuring cooling air circulation.
Implementation Method 1
During rotation, the ring bears against the platforms by centrifugal force with a relatively significant load
Implementation Method 2
since the ratio of thermal expansion with increasing temperature is between two and three, the differential expansions during operation between the rod on one side, and the blades and disc on the other, risk either exacerbating the stresses on the platforms or creating gaps
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
The invention concerns a rotary assembly for a turbomachine, comprising: - a disk (16) having an outer periphery having an alternation of cavities (22) and teeth (20), - blades (14) extending radially from the disk (16) and of which the roots (24) are engaged axially and held radially in the cavities (22) of the disk, - platforms (30) extending circumferentially from the blades (14) and arranged circumferentially end-to-end, facing each other, - upstream and/or downstream sealing means for axially sealing an annular area extending radially from the platforms (30) to the disk. According to the invention, the sealing means comprise, radially, an annular inner portion (64) and an annular outer portion (66) structurally separate from each other, and of which the opposing radial ends are capable of moving radially relative to each other by sealingly sliding, only the centrifugal forces of the outer portion (66) being transferred in rotation to the platforms (30).