Passive Clearance Control for Centrifugal Impeller Shroud
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Solution Overview
Problem
Centrifugal compressor systems face challenges in maintaining optimal blade tip clearance to prevent rub and leakage, as existing adjustment systems are complex, heavy, and power-intensive, and fail to address misalignment caused by operational deflection of the centrifugal impeller.
Innovation Solution
A dynamically moveable centrifugal impeller shroud assembly with a flexible shroud arm and thermal member, where the thermal member has a lower coefficient of thermal expansion than the shroud, allowing for passive adjustment of the shroud position and shape in response to temperature and pressure changes, thereby maintaining clearance and resolving misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the blade tip clearance is set to avoid rub during transients with greatest closure, then reliability is improved, but leakage increases and efficiency deteriorates
Solution Approach 1:
The shroud is made dynamically moveable through a flexible shroud arm that allows the shroud to adjust its position in response to differential pressure changes between inlet and outlet cavities, enabling real-time clearance optimization rather than fixed clearance design
Solution Approach 2:
The system changes the physical state of the shroud from fixed to moveable by utilizing pressure differential as a control parameter, allowing the shroud position to vary with operating conditions to maintain optimal clearance
2Reliability
If active actuation systems are used to adjust blade tip clearance, then clearance control is improved, but device complexity, weight, and power consumption increase
Solution Approach 1:
The shroud system serves itself by using the inherent differential pressure from the compressor operation to automatically adjust its position through the flexible shroud arm, eliminating the need for external actuation systems
Solution Approach 2:
The patent replaces complex active mechanical actuation systems with a passive flexible mechanical structure that responds to pressure differentials, substituting sophisticated control mechanisms with a simple elastic deformation-based system
3Stability of the object's composition
If the shroud is rigidly mounted to the engine casing, then structural stability is improved, but adaptability to operational changes deteriorates
Solution Approach 1:
The shroud mounting is segmented into a rigid portion (casing connection) and a flexible portion (shroud arm), allowing the rigid part to provide stability while the flexible part provides adaptability for clearance adjustment
Solution Approach 2:
The shroud arm incorporates a flexible portion that can deform elastically in response to pressure differentials, providing the necessary adaptability while maintaining structural integrity through its flexible design
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 solution passively maintains the clearance gap and resolves misalignment between the shroud and impeller, simplifying the design, reducing weight and power requirements, and improving efficiency and operability of the centrifugal compressor by using both thermal and mechanical mechanisms to adapt to operational changes.
Implementation Method 1
The flexible portion is configured to flex responsive to a differential pressure between the first cavity and the second cavity
Implementation Method 2
The thermal member has a coefficient of thermal expansion (CTE) lower than the CTE of the shroud
Data Source
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AI summary
A centrifugal impeller shroud assembly (300) has a dynamically moveable impeller shroud (320) for encasing a rotatable centrifugal impeller (111) and resolving misalignment between the impeller shroud and the rotatable centrifugal impeller. The assembly comprises a static casing (371), an impeller shroud (320), a shroud arm (370), and a thermal member (360). The shroud arm is coupled between the casing and the impeller shroud. The thermal member is coupled to the impeller shroud and has a coefficient of thermal expansion (CTE) lower than the CTE of the shroud. The shroud arm comprises a flexible portion (372) configured to flex responsive to a differential pressure across the shroud arm.