Intershaft Seal Retaining Ring Radial Growth Control
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Solution Overview
Problem
Intershaft seals in gas turbine engines face issues with leakage, wear, and increased frictional forces due to centrifugal loading and thermal expansion, leading to inefficient sealing and potential contact between components, which affects performance and longevity.
Innovation Solution
The use of a sealing ring with a main body of a first material and a retaining ring of a second material with higher stiffness and thermal expansion coefficient, which reduces radial growth and contraction, respectively, to control interference and clearance between the sealing ring and the outer shaft, thereby minimizing frictional forces and maintaining a consistent seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carbon ring is allowed to expand freely under centrifugal loading, then the sealing contact with the outer shaft is maintained, but the radial growth causes increased frictional forces and potential contact between the ring and shaft
Solution Approach 1:
The sealing ring is segmented into two functional parts: a carbon body for sealing and a retaining ring for dimensional control. This segmentation allows each part to perform its specific function independently - the carbon body maintains sealing contact while the retaining ring restricts radial growth to minimize frictional forces.
Solution Approach 2:
The patent changes the physical parameters of the sealing ring by adding a retaining ring with specific stiffness properties. This retaining ring has a stiffness of at least 100 GN/m², which is sufficient to restrict radial growth of the carbon body under centrifugal loading, thereby controlling the frictional forces while maintaining sealing reliability.
2Reliability
If the distance between runners is reduced to improve sealing, then leakage is decreased, but thermal expansion and manufacturing tolerances cannot be accommodated
Solution Approach 1:
The patent employs dynamic adjustment of the sealing clearance through the retaining ring mechanism. The retaining ring allows the carbon body to expand thermally and accommodate manufacturing tolerances while maintaining a controlled minimum clearance from the runners. This dynamic capability enables the seal to adapt to varying conditions without requiring reduced runner spacing.
Solution Approach 2:
The retaining ring acts as an intermediary between the carbon body and the runners. It mediates the interaction by controlling the radial position of the carbon body, ensuring that thermal expansion and manufacturing variations do not result in excessive clearance or contact with the runners, thereby maintaining sealing effectiveness.
3Reliability
If lift generating formations are added to prevent rubbing contact, then wear is reduced, but the complexity of the seal structure increases
Solution Approach 1:
The patent replaces the need for lift generating formations (mechanical complexity) with a centrifugal force-based solution. The retaining ring, under centrifugal loading, automatically positions the carbon body to maintain optimal clearance from the runners, eliminating rubbing contact and wear without requiring additional lift-generating structures.
4Reliability
If the carbon ring is designed with tight clearance for optimal sealing, then leakage is minimized, but any variation in tolerances or wear leads to inconsistent sealing performance
Solution Approach 1:
The patent changes the clearance parameter dynamically through the retaining ring mechanism. Instead of relying on fixed tight clearances that are sensitive to manufacturing tolerances, the retaining ring actively maintains a consistent effective clearance by restricting radial growth of the carbon body, thereby compensating for tolerance variations and wear throughout the seal's operational life.
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 reduces frictional resistance and prevents contact, maintaining a consistent seal and reducing wear, even under varying conditions such as centrifugal loading and temperature changes, thereby enhancing the performance and longevity of the intershaft seal.
Implementation Method 1
the retaining ring reduces or prevents radial growth of the sealing ring relative to the outer shaft under centrifugal loading
Implementation Method 2
a retaining ring fitted to the radially outward side of the body portion and formed of a second material having a second stiffness, the second stiffness being greater than the first stiffness
Implementation Method 3
the second material having a second stiffness and a second coefficient of thermal expansion, the second coefficient of thermal expansion being higher than the first coefficient of thermal expansion such that the retaining ring increases radial contraction of the sealing ring relative to the outer shaft on decreasing temperature
Implementation Method 4
If this lift can be sufficiently strong such that an air film is produced and no axial rubbing contact occurs under normal operation
Data Source
AI summary
An intershaft seal is provided for inner and outer coaxial shafts which rotate relative to each other. The seal is located in an annular space between the shafts and maintains an axial pressure differential between a fluid pressure on the first side of the seal and a different fluid pressure on the other, second side of the seal. The seal includes a first runner which extends circumferentially around a first one of the shafts and projects therefrom into the annular space. The seal further includes a sealing ring which is coaxial with the shafts.