Segmented Inner Shroud Stiffness Modification for Vibration Control
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Solution Overview
Problem
Existing axial turbomachine stators with segmented inner shrouds face destructive vibration modes due to the flexibility of abradable material and significant radial thicknesses of bosses and notches, which affect the vibratory response and assembly of the rectifier.
Innovation Solution
Incorporating a thin, flexible profile that extends continuously along the inner surface of the shroud, cooperating with means for hooking the inner ends of the blades, and positioned within a layer of abradable material to modify the stiffness at segment junctions, thereby reducing destructive vibratory modes without increasing the mass or inertia of the shroud.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a segmented inner shroud with bosses and notches is used to retain blade ends, then the assembly and retention of blades is facilitated, but the radial thickness of bosses and notches increases the mass and inertia of the shroud, negatively impacting vibratory response
Solution Approach 1:
The patent applies this principle by using a thin abradable material layer (typically 0.5-2mm thick) deposited on the inner shroud surface instead of thick rigid bosses and notches. This abradable layer provides the necessary retention function while maintaining minimal thickness, thereby reducing the shroud's mass and inertia without compromising blade retention capability.
Solution Approach 2:
The patent changes the physical state and properties of the retention structure by using abradable material with specific mechanical properties (softer, more compliant) rather than rigid metal bosses and notches. This parameter change allows the retention features to be integrated into the shroud surface with minimal thickness reduction, optimizing the mass-inertia characteristics while maintaining retention function.
2Reliability
If abradable material is deposited on the inner shroud surface to provide sealing, then sealing between compressor stages is improved, but the flexibility of the abradable material causes the shroud to exhibit destructive vibration modes under frequency excitations
Solution Approach 1:
The patent uses a thin film of abradable material deposited on the inner shroud surface to provide sealing between compressor stages. This thin flexible layer maintains sealing reliability while minimizing the mass and stiffness that would otherwise contribute to destructive vibration modes, thereby improving vibratory response stability.
Solution Approach 2:
The patent employs composite construction by depositing abradable material (such as metal powder, ceramic, or polymer composites) onto the inner shroud surface. This composite structure combines the sealing functionality of the abradable layer with the structural integrity of the underlying shroud, achieving both reliable sealing and improved vibration characteristics.
3Ease of operation
If the openings in the inner shroud are made larger to facilitate blade end insertion, then the ease of assembly is improved, but the difference in size must be filled with additional material, increasing the shroud thickness and mass
Solution Approach 1:
The patent uses a thin abradable material layer to line the inner shroud surface, allowing for larger openings that facilitate blade end insertion without requiring additional filling material. The abradable layer provides the necessary surface compliance and sealing while maintaining minimal thickness, thereby enabling easier assembly without increasing shroud mass.
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 effectively modifies the frequency behavior of the inner shroud, preventing destructive vibrations while maintaining flexibility and reducing assembly complexity, allowing for improved anchoring and damping of high-frequency vibrations.
Implementation Method 1
a layer of abradable material is deposited on each inner surface of the inner shrouds
Implementation Method 2
The profile remains flexible, it does not form a reinforcement completely blocking the junctions between the segments. This choice to retain a certain flexibility is sufficient to stem the destructive vibratory modes of the inner shroud.
Data Source
AI summary
The stator has blades whose annular ring is provided to be extended radially. An inner shell is provided through which the inner tips of the blades pass, and provided with annular segments arranged end to end. A strip is provided to be extended circumferentially along the length of the inner surface of the shell and provided for mating with an engaging element for engaging the inner tips of the blades for retention, and provided to be extended continuously along adjacent annular segments. An independent claim is included for a compressor of axial turbomachine.