Piston Seal Ring Groove Venting for Axisymmetric Leakage
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Solution Overview
Problem
Piston seal rings (PSRs) in gas turbine engines experience non-axisymmetric leakage due to manufacturing errors, operational loads, and wear, leading to thermal hotspots, mass unbalance, and reduced sealing performance, exacerbated by factors like torque, thrust loads, and differential thermal expansion.
Innovation Solution
Incorporating circumferentially distributed venting features in the form of radial channels on both axial end walls of the groove that accommodate the PSR, allowing controlled leakage to offset non-axisymmetric leakage and reduce thermal asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the piston seal ring is made small in cross section to be compliant, then the seal ring can accommodate dynamic loading and relative movement, but the seal ring has little hoop strength and twist resistance, leading to non-axisymmetric leakage and thermal hotspots
Solution Approach 1:
The seal ring is segmented into multiple circumferential sections with gaps between them, allowing the ring to flex and adapt to dynamic loading while maintaining sealing effectiveness. The segmentation enables the ring to accommodate relative movement between the shaft and seal runner without requiring excessive hoop strength in a continuous structure.
Solution Approach 2:
The seal ring cross-section is made asymmetric with different thicknesses at different circumferential positions. This asymmetric design provides varying compliance characteristics around the ring, allowing it to better accommodate non-axisymmetric loading conditions and thermal gradients while maintaining adequate sealing contact.
2Ease of manufacture
If manufacturing errors and wear occur, then the seal ring can be assembled and operated, but non-axisymmetric leakage occurs leading to thermal hotspots and mass unbalance
Solution Approach 1:
The seal ring is pre-formed with an asymmetric cross-section and circumferential gaps during manufacturing, anticipating future wear and manufacturing variations. This preliminary design compensates for expected deviations, ensuring that even as the ring wears or experiences manufacturing tolerances, it maintains adequate sealing performance and prevents thermal hotspots.
Solution Approach 2:
The seal ring design incorporates variable cross-sectional dimensions and gap sizes that can be adjusted based on operating conditions. By changing geometric parameters such as ring thickness, gap width, and asymmetric profile, the seal can accommodate manufacturing errors and wear while maintaining reliable sealing and thermal symmetry throughout its service life.
3Reliability
If the seal ring seats against one sidewall due to pressure difference, then sealing occurs, but dynamic components cause unseating at one side leading to non-axisymmetric leakage
Solution Approach 1:
The seal ring is designed with dynamic characteristics that allow it to adapt its seating position based on instantaneous loading conditions. The compliant asymmetric structure enables the ring to dynamically adjust its contact points with the groove sidewalls, maintaining sealing effectiveness while accommodating the continuous unseating and reseating caused by pressure differences and dynamic components.
Solution Approach 2:
The seal ring accommodates periodic unseating and reseating actions that occur during operation due to pressure fluctuations and dynamic loading. The asymmetric design with circumferential gaps allows the ring to undergo repeated cycles of contact and separation without losing overall sealing performance, effectively managing the periodic nature of the unseating phenomenon.
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
The venting features mitigate thermal asymmetry and enhance sealing performance by maintaining an axisymmetric leakage, reducing localized thermal distortions and stress concentrations.
Implementation Method 1
In an operational condition where there is a pressure difference across the PSR, optimally, one axial end face of the PSR will bear against and seal against the adjacent sidewall face of the groove
Implementation Method 2
These thermal hotspots may in turn, lead to non-axisymmetric distortion of the contacting structure resulting in mass unbalance, localized stress concentrations, and reduced sealing performance
Data Source
AI summary
A machine comprising a rotor having: an inner member; an outer member encircling the inner member; and a groove in one of the inner member and the outer member. The groove has a first side wall, a second side wall and a base. A split ring seal is accommodated in the groove and contacts a surface of the other of the inner member and the outer member The first side wall has a plurality of open radial first channels and the second side wall has a plurality of open radial second channels.