Leaned Centrifugal Compressor Airfoil Diffuser Design
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Solution Overview
Problem
Centrifugal compressors face limitations in operating range and efficiency due to flow choking and secondary flow phenomena at the impeller exit, particularly in cryogenic rectification systems, where conventional two-dimensional low solidity airfoil diffusers fail to effectively manage flow angles and boundary layer stability.
Innovation Solution
The implementation of airfoil diffusers with blades having a lean angle greater than zero degrees and variable or equal hub and shroud stagger angles, which realigns the diffuser blades with the flow direction and redistributes pressure loading to stabilize the boundary layer and suppress secondary flows, thereby extending the operating range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional two-dimensional low solidity airfoil diffusers are used, then the diffuser achieves compact design and reasonable pressure recovery, but the operating range is limited due to flow choking and secondary flow phenomena
Solution Approach 1:
The patent transitions from conventional two-dimensional airfoil diffusers to three-dimensional leaned airfoil diffusers. The blade lean angle introduces a third dimension (spanwise orientation) to the diffuser blade geometry, enabling the blades to better align with the three-dimensional flow structure exiting the impeller. This dimensional enhancement allows the diffuser to accommodate a wider range of flow conditions and angles, thereby extending the operating range while suppressing harmful secondary flows through improved flow alignment.
Solution Approach 2:
The patent applies different geometric characteristics to different regions of the diffuser blades. Specifically, the blade lean angle varies along the span from hub to shroud, with the hub stagger angle differing from the shroud stagger angle. This local variation in blade orientation optimizes the alignment with the local flow direction at each radial position, improving pressure recovery and reducing flow separation in specific regions while maintaining overall compact design.
2Stress or pressure
If the diffuser blade solidity is increased to improve pressure recovery, then pressure recovery levels increase, but the diffuser becomes less compact and the operating range decreases due to flow choking
Solution Approach 1:
The patent changes the geometric parameters of the diffuser blades, specifically introducing a lean angle greater than zero degrees and optimizing the solidity ratio. By adjusting these parameters, the blades achieve better alignment with the flow direction, which improves pressure recovery efficiency. This allows the diffuser to maintain compact dimensions while achieving higher pressure recovery levels without increasing diffuser volume or causing flow choking.
3Adaptability or versatility
If additional control mechanisms are added to extend operating range, then the operating range increases, but the device complexity and manufacturing costs increase
Solution Approach 1:
The leaned airfoil diffuser design is inherently adaptive to varying flow conditions through its three-dimensional geometry. The blade lean angle and stagger angle configuration enable the diffuser to automatically adjust to different operating points without requiring external control mechanisms. This self-adapting geometry extends the operating range while maintaining simple construction and avoiding additional complexity.
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 significantly increases the operating range and efficiency of the compressor stage by delaying stall and separation, reducing manufacturing costs, and improving pressure recovery, making it suitable for varying process demands in cryogenic air separation plants without the need for additional control mechanisms.
Implementation Method 1
realigns the diffuser blades with the flow direction
Implementation Method 2
redistributes pressure loading to stabilize the boundary layer
Implementation Method 3
suppress secondary flows
Implementation Method 4
delaying stall and separation
Data Source
AI summary
A low solidity vaned airfoil diffuser for a centrifugal compressor wherein each blade has a lean angle greater than zero and wherein the hub stagger angle may be the same as or may be different from the shroud stagger angle for each blade.