Rotary Machine Seal Fin Root Thickness Optimization
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Solution Overview
Problem
The seal fin in rotary machines, such as steam turbines and gas turbines, faces challenges in preventing fluid leakage while maintaining structural strength against differential pressure, leading to a trade-off between leakage prevention and strength reduction.
Innovation Solution
A seal member is designed with a first fin and a second fin, where the second fin has a thicker root and wider width on the low-pressure side, providing enhanced strength and preventing leakage by positioning the second fin on the low-pressure side of the first fin, and potentially using a higher-strength material for the second fin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a seal fin is provided to prevent fluid leakage, then leakage prevention performance is improved, but structural strength decreases due to the differential pressure acting on the fin
Solution Approach 1:
The patent applies local quality by making the root thickness of the second fin greater than that of the first fin. Specifically, the root thickness of the second fin is set to 1.5-3.0 times that of the first fin, creating a localized reinforcement at the root where stress concentration occurs. This allows the seal fin to maintain adequate strength at the critical root region while preserving the sealing functionality of the fin structure.
Solution Approach 2:
The patent introduces a dimensional variation by positioning the second fin on the low-pressure side from the first fin in the rotation axis direction. This spatial arrangement in the axial dimension allows the thicker second fin to counteract the differential pressure loads without interfering with the sealing action of the first fin, effectively using the axial dimension to resolve the strength-leakage prevention trade-off.
2Strength
If the fin thickness is increased to improve strength, then structural strength is improved, but the leakage prevention performance may be compromised due to altered fluid flow characteristics
Solution Approach 1:
The patent applies local quality by selectively increasing the root thickness of the second fin while keeping the tip thickness and overall fin geometry similar to the first fin. This localized thickening at the root provides the necessary structural strength to withstand differential pressure without significantly altering the fluid flow characteristics along the fin length, thereby maintaining effective leakage prevention.
Solution Approach 2:
The patent segments the seal fin structure into multiple fins (first fin and second fin) with different thickness characteristics. The first fin maintains a standard thickness optimized for sealing, while the second fin has an increased root thickness for strength. This segmentation allows each fin to perform its specific function optimally without compromising the other.
Data Source
AI summary
A seal member is disposed between a rotor and a stator to provide a seal between the rotor and the stator. The seal member comprises: a rotary-side member fixed to a surface of the rotor opposing the stator; a fixed-side member fixed to the stator and facing the rotary-side member; and a first fin and a second fin which are disposed on one of the rotary-side member and the fixed-side member, the first fin protruding on the opposing surface side, the second fin being disposed on a lower pressure side in a rotating axis direction relative to the first fin and protruding on the opposing surface side. The thickness, in the rotating axis direction, of the second fin at the root thereof is greater than the thickness, in the rotating axis direction, of the first fin at the root thereof.