Floating Non-Contact Seal Clearance Offset for Balanced Beam Stress
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Solution Overview
Problem
Existing sealing systems in aircraft engines experience material fatigue due to an imbalance in radial deflection of the shoe, leading to non-zero mean stress values, which reduces seal lifetime.
Innovation Solution
A four-bar linkage is introduced with angled beams relative to the shoe, and the cold-build gap is adjusted to center the shoe's position within the range of deflections, ensuring equal outward and inward deflection distances to eliminate mean stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the shoe is allowed to deflect radially during operation to maintain clearances, then sealing performance is improved, but material fatigue increases due to non-zero mean stress
Solution Approach 1:
The patent applies asymmetry by offsetting the shoe's neutral position from the center of the cold build gap. The shoe is positioned such that its neutral position is located at a specific offset distance from the center of the cold build gap, creating asymmetric clearance distribution. This asymmetric positioning ensures that the shoe experiences equal magnitude deflections in both inward and outward directions, balancing the stress cycle and eliminating non-zero mean stress, thereby reducing material fatigue while maintaining effective sealing clearance.
2Manufacturing precision
If the cold build gap is used to account for build tolerances, then assembly clearance is improved, but deflection imbalance occurs leading to mean stress
Solution Approach 1:
The patent applies preliminary action by pre-positioning the shoe at an offset neutral position during assembly, rather than at the center of the cold build gap. This preliminary offset positioning is calculated based on expected deflection characteristics, so that when the seal operates, the shoe's deflections are balanced around this offset position. This preliminary action eliminates mean stress by ensuring equal probability of inward and outward deflections, while the cold build gap still provides sufficient clearance for manufacturing tolerances.
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 balances the seal, reducing material fatigue and enhancing seal lifetime by minimizing mean stress on the seal beams.
Implementation Method 1
As the air flows passes teeth 238 of the shoe 236 (where the teeth 238 are frequently formed as thin knife-edges), an associated pressure field changes. This change induces the shoe 236 to move, e.g., in the radial reference direction until an equilibrium condition is obtained.
Data Source
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Figure 2B
AI summary
Aspects of the disclosure are directed to an engine (10) comprising: a first structure (206), a second structure (212) configured to rotate relative to the first structure (206), and a floating, non-contact seal (218) that interfaces the first structure (206) and the second structure (212), where the seal (218) includes: a shoe (236), a first beam (230a) coupled to the shoe (236), and a second beam (230b) coupled to the shoe (236), where during a non-operational state of the engine (10) a reference point (398) of the shoe (236) is substantially centered within a range of radial deflections (394a, 396a) of the reference point (398) of the shoe (236) over the operating range of the engine (10).