Hydrostatic Seal Tooth Geometry for Faster Maneuver Response
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Solution Overview
Problem
Hydrostatic seals in gas turbine engines can become 'stuck' due to high friction forces, leading to undesirable contact with the rotor during maneuver conditions, as the friction force may exceed the aerodynamic and mechanical forces acting on the seal shoe, preventing it from responding to rapid gap changes.
Innovation Solution
A hydrostatic seal design featuring a shoe with radially extending teeth, where the axial distance from the forward end to the longest tooth is greater than the radial distance from the tooth tip to the sealing surface, providing a lift force that is equal to or greater than two times the friction force, ensuring the seal can overcome friction and maintain proper clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the seal shoe is designed with larger piston area to increase aerodynamic forces, then the seal can maintain tighter clearances, but the friction force increases proportionally which may cause the seal to become stuck
Solution Approach 1:
The patent introduces a mechanical lift force mechanism that acts as a counterbalancing force to offset the friction force. The lift force is generated through a mechanical linkage system connected to the seal shoe, providing an opposing force that prevents the seal from becoming stuck due to excessive friction, thereby resolving the contradiction between maintaining tight clearances and ensuring maneuver response.
Solution Approach 2:
The patent modifies the force balance parameters by introducing a mechanical lift force component that changes the overall force acting on the seal shoe. This parameter change ensures that the net force (aerodynamic force plus mechanical lift force) remains sufficient to overcome friction during maneuver conditions, allowing the seal to respond rapidly to gap changes while maintaining tight clearances during normal operation.
2Ease of operation
If the friction force is reduced to improve maneuver response, then the seal can track rapid gap changes, but the aerodynamic forces may be insufficient to maintain tight clearances
Solution Approach 1:
The patent merges two force mechanisms - aerodynamic forces and mechanical lift force - to work together in maintaining seal clearance. The aerodynamic forces provide the primary sealing action during normal operation, while the mechanical lift force provides additional support during maneuver conditions, allowing the seal to maintain tight clearances without requiring excessive friction resistance.
Solution Approach 2:
The mechanical lift force serves as a counterbalancing force that compensates for situations where aerodynamic forces alone are insufficient to overcome friction during maneuver conditions. This allows the seal to maintain adequate clearance without requiring the aerodynamic forces to be excessively high, which would otherwise increase friction and prevent maneuver response.
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 enhanced seal design ensures that the lift force is sufficient to prevent seal lock-up, maintaining effective clearance and preventing undesirable contact with the rotor, even under maneuver conditions, thereby improving the seal's maneuver response and longevity.
Implementation Method 1
aerodynamic forces developed between the seal shoe and a rotor surface during operation
Implementation Method 2
when a pressure differential is developed across the seal
Implementation Method 3
a friction force develops which is proportional to the geometry of the seal (piston area) and the aerodynamic forces acting on the seal
Data Source
AI summary
A hydrostatic seal configured to be disposed between relatively rotatable components includes a base. The seal also includes a seal housing. The seal further includes a shoe operatively coupled to the base and extending axially from a forward end to an aft end. The seal yet further includes a plurality of teeth extending radially from a sealing surface of the shoe, one of the teeth being a longest tooth that extends furthest radially from the sealing surface, the axial distance from the forward end of the shoe to the longest tooth being greater than a radial distance from a radial tooth tip to the sealing surface.