Bidirectional Shaft Seal Segment for Gas Film Maintenance
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Solution Overview
Problem
Existing circumferential gas film seals are directional, failing to maintain an effective gas film when the sleeve rotates in the opposite direction, leading to increased friction and wear, particularly in scenarios like 'windmilling' in jet engines.
Innovation Solution
A bidirectional circumferential shaft seal segment design featuring radial outer and inner faces, axial faces, and bidirectional lifting means with bleed slots and recesses that extend in opposite circumferential directions, ensuring a gas film is maintained regardless of the sleeve's rotation direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circumferential gas film seal uses recesses configured for unidirectional rotation, then the seal maintains an effective gas film in the intended rotation direction, but the seal fails to maintain the gas film when the sleeve rotates in the opposite direction
Solution Approach 1:
The seal segment incorporates asymmetric recesses on its sealing surface that are specifically configured to generate hydrodynamic lift forces. These recesses have non-symmetric geometries that create pressure differentials effective in one rotation direction. The patent applies asymmetry by designing the recess shape and position to optimize performance for the intended rotation direction while acknowledging the limitation in reverse rotation.
Solution Approach 2:
The patent addresses bidirectional rotation by installing two seal segments with opposite orientations. One seal segment has recesses configured for clockwise rotation, while the other has recesses configured for counter-clockwise rotation. This inversion principle allows the seal assembly to maintain effective gas film formation regardless of rotation direction, as one seal will be optimally oriented for the actual rotation direction.
2Reliability
If a contact circumferential shaft seal is used, then leakage control is very effective, but the seal rings wear out quickly at high rotation speeds
Solution Approach 1:
The patent employs a gas film seal mechanism that uses pressurized gas to create a hydrodynamic film between the seal segment and the rotating sleeve. Gas is supplied through the recesses in the seal segment, and the rotating sleeve entrains this gas to generate pressure that lifts the seal segment off the sleeve surface. This pneumatic mechanism eliminates direct solid contact, reducing friction and wear while maintaining effective sealing, thereby extending seal life at high rotation speeds.
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 solution provides a robust, bidirectional seal that reduces friction and wear, maintaining separation between the seal and sleeve in both rotation directions, enhancing durability and reliability, especially in high-speed and windmilling conditions.
Implementation Method 1
configured to maintain a gas film between the seal and the sleeve when the sleeve rotates in either of first and second opposite directions relative to the seal
Implementation Method 2
hydrodynamic sealing can be produced by forming recesses or cutouts on the side of the seal ring that faces the sleeve. As the sleeve rotates, air entrained by the rotating sleeve is compressed in these cutouts, and as it escapes over the non-recessed 'pads' between the recesses, it produces an additional pressure and flow of air for maintaining a separation between the seal ring and the sleeve
Implementation Method 3
The light contact force is achieved by routing high pressure gas to opposing faces through clearance spaces and milled cutouts. In the case of a contacting circumferential seal, the outer diameter of the ring is exposed across its entire width while the inside diameter is exposed across its entire width except for the width of a small sealing dam. This creates an imbalance in force that lightly seats the seal against the rotating sleeve. Producing a force balanced contact in this manner is referred to hydrostatic sealing
Data Source
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AI summary
A circumferential shaft seal segment includes a radial outer face, a radially inner face, a first axial face extending from the radial outer face to the radial inner face and a second axial face axially spaced from the first axial face and extending from the radially outer face to the radially inner face. The seal has a bleed slot (84) in the radially inner face extending from the first axial face toward the second axial face, and there are first (86) and second (88) recesses in the radially inner face in communication with the bleed slot (84) that extend from circumferentially opposite sides of the bleed slot (84).