Compressor Stator Vane Asymmetry for Fatigue Reduction
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Solution Overview
Problem
In axial flow compressors, equal stator vane counts in upper and lower compressor casing halves can lead to vibratory responses in rotating blades, causing high cycle fatigue, and existing methods for altering blade counts are impractical as they require costly rotor removal.
Innovation Solution
A method to retrofit compressors by increasing the stator vane count in the upper compressor casing half while maintaining the same count in the lower half, allowing for non-uniform blade counts between the two halves without removing the rotor, thereby reducing vibratory responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If equal stator vane counts are used in upper and lower compressor casing halves, then manufacturing and assembly are simplified, but vibratory response in rotating blades increases causing high cycle fatigue
Solution Approach 1:
The patent applies asymmetry by configuring the upper compressor casing half with a different number of stator vanes than the lower casing half. Specifically, the upper half contains 23 stator vanes while the lower half contains 25 stator vanes, creating a non-uniform blade count distribution. This asymmetric configuration disrupts the synchronous vibratory response that occurs with equal blade counts, thereby reducing high cycle fatigue in rotating blades while maintaining manufacturing feasibility through modular half-casing design.
2Reliability
If non-uniform stator vane counts are implemented to reduce vibratory response, then blade reliability improves, but rotor removal is required for modification
Solution Approach 1:
The patent applies segmentation by dividing the compressor casing into separable upper and lower halves, each containing stator vanes that can be independently configured. The upper half with 23 stator vanes can be removed and replaced with a different configuration without affecting the lower half containing 25 stator vanes. This modular segmentation enables field modification of the blade count distribution to reduce vibratory response while avoiding the need for rotor removal, significantly improving ease of repair and maintenance.
3Reliability
If stator vane count is changed in the field, then vibratory response is reduced, but maintenance cost increases due to rotor removal
Solution Approach 1:
The patent applies segmentation by dividing the compressor casing into separable upper and lower halves, each containing stator vanes that can be independently configured. The upper half with 23 stator vanes can be removed and replaced with a different configuration without affecting the lower half containing 25 stator vanes. This modular segmentation enables field modification of the blade count distribution to reduce vibratory response while avoiding the need for rotor removal, significantly improving ease of repair and maintenance.
4Adaptability or versatility
If equal blade counts are maintained in existing compressors, then existing configurations remain compatible, but synchronous vibratory response causes high cycle fatigue
Solution Approach 1:
The patent applies asymmetry by configuring the upper compressor casing half with a different number of stator vanes than the lower casing half. Specifically, the upper half contains 23 stator vanes while the lower half contains 25 stator vanes, creating a non-uniform blade count distribution. This asymmetric configuration disrupts the synchronous vibratory response that occurs with equal blade counts, thereby reducing high cycle fatigue in rotating blades while maintaining manufacturing feasibility through modular half-casing design.
Solution Approach 2:
The patent applies dynamics by enabling the blade count configuration to be changed in the field through removal and replacement of the upper casing half. This allows the compressor to adapt its stator vane distribution (23 in upper half, 25 in lower half) to optimize performance and reduce vibratory response, transforming a static equal-blade-count design into a dynamically adjustable asymmetric configuration that improves reliability without sacrificing adaptability.
Data Source
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AI summary
Stator blade counts of an upper compressor casing for adjacent stages S0 and S1 are changed in the field to provide additional stator vanes and hence an increased vane count. Particularly, the upper casing half (30) of the compressor is removed from the lower casing half. The original stator vanes (31) on opposite axial sides of the first stage buckets are removed from the upper casing half (30) and replaced by an additional sets of stator vanes (33) providing a non-uniform vane spacing as between the upper and lower halves of the compressor as well as between axially adjacent stages S0 and S1. The unequal vane counts reduce the vibratory response of the rotating blades between stages S0 and S1.