Labyrinth Seal Packing Ring with Passive Feedback
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Solution Overview
Problem
Labyrinth seals in turbomachinery are prone to excessive leakage and rotor-rub due to rigid design, which can lead to damage and inefficiency, especially during rotor transients like thermal distortions and critical speed passages, as they cannot adjust clearance dynamically.
Innovation Solution
A progressive clearance labyrinth seal design featuring an arcuate plate, a circumferentially-segmented packing ring with progressively decreasing tooth clearances, and a biasing member that moves radially in response to hydrostatic forces, eliminating the need for a steam-seal joint to reduce friction and allow passive feedback adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large clearance is configured between the rotor and seal to prevent rotor-rub, then rotor contact is avoided, but leakage increases and efficiency decreases
Solution Approach 1:
The packing ring is designed to dynamically adjust its radial position based on operating conditions. During transient conditions, the ring moves outward to maintain larger clearance and prevent rotor-rub. During steady-state operation, it moves inward to reduce clearance and minimize leakage, thus resolving the contradiction between reliability and energy loss
Solution Approach 2:
The seal incorporates passive feedback mechanisms where the differential pressure across the seal and hydrostatic forces automatically regulate the packing ring position. When clearance increases, hydrostatic forces push the ring inward; when clearance decreases, outward forces dominate, creating a self-regulating system that balances rotor protection with leakage prevention
2Device complexity
If a rigid labyrinth seal is used, then structural simplicity is maintained, but the seal cannot adjust clearance during rotor transients
Solution Approach 1:
The packing ring is designed with radial mobility capability, allowing it to move between stationary and dynamic positions. This dynamic feature enables the seal to adapt to varying rotor positions during transients while maintaining a relatively simple overall structure compared to active control systems
Solution Approach 2:
The seal utilizes self-regulating hydrostatic forces and differential pressure to automatically adjust the packing ring position without external control systems. The structure serves itself by using the process fluid pressure to maintain optimal clearance, eliminating the need for complex actuators or control mechanisms
3Reliability
If a VCPPP ring with steam-seal joint is used, then rotor-rub is prevented during transients, but friction at the joint introduces hysteresis and rotor-rubs occur after closing
Solution Approach 1:
The invention removes the problematic steam-seal joint from the packing ring design. By eliminating this joint, the source of friction and hysteresis is extracted from the system, allowing the packing ring to move freely in the radial direction without resistive forces that cause delayed response and rotor-rub after closing
Solution Approach 2:
The mechanical connection through a steam-seal joint is replaced with a design that allows direct radial movement of the packing ring. This substitution eliminates the mechanical friction interface and replaces it with a smoother movement mechanism that responds more quickly to clearance changes
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 design maintains a small clearance during transients, reducing leakage and enhancing efficiency by using passive feedback forces to adjust the packing ring's position, thus minimizing damage and leakage without requiring additional sensors or actuators.
Implementation Method 1
The progressive decrease in the clearances of the teeth creates a passive feedback in the hydrostatic forces generated by differential pressure across the seal assembly
Implementation Method 2
a biasing member disposed intermediate to the arcuate plate and the packing ring and coupled to both
Data Source
AI summary
A seal assembly for a turbomachine may include at least one arcuate plate coupled to an interior surface of a stationary housing; a circumferentially-segmented packing ring disposed intermediate to a rotor and the plate; a plurality of arcuate teeth disposed intermediate to the ring and the rotor, wherein a clearance of each tooth decreases progressively going from an upstream side of the turbomachinery to a downstream side; wherein the progressive decrease in the clearances of the teeth creates a passive feedback, such that as a tip clearance decreases, outward radial forces cause the packing ring to move away from the rotor and as the tip clearance increases, inward radial forces cause the packing ring to move toward the rotor; and a biasing member disposed intermediate to the arcuate plate and the ring and coupled to both.