Asymmetric Casing Treatment for Centrifugal Compressor Stability
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Solution Overview
Problem
Centrifugal compressors face instability and reduced efficiency at low flow rates due to non-uniform fluid pressure distribution in the circumferential direction, which limits their stable operating range and leads to phenomena like stall and surge.
Innovation Solution
An asymmetric self-recirculating casing treatment is implemented, where the axial-direction position and width of the suction ring groove are varied in the circumferential direction to reduce non-uniformity in fluid pressure distribution, enhancing the recirculation of fluid via a back-flow channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a symmetric suction ring groove is used in the casing treatment, then the manufacturing and design are simplified, but the non-uniform pressure distribution in the circumferential direction cannot be compensated, limiting the extension of stable operating range
Solution Approach 1:
The suction ring groove is designed with asymmetric axial-direction positions in the circumferential direction, where the axial position varies at different circumferential locations. This asymmetric configuration compensates for the non-uniform pressure distribution generated by the scroll channel, enabling better control of fluid flow and extension of the stable operating range without complicating manufacturing processes
Solution Approach 2:
Different portions of the suction ring groove are positioned at different axial distances from the impeller full blade leading edge in the axial direction, creating local variations in groove depth and position. This allows each circumferential region to be optimized for its specific pressure conditions, improving overall compressor stability while maintaining a relatively simple groove structure
2Reliability
If the axial-direction position of the suction ring groove is made asymmetric, then the stable operating range is extended by compensating non-uniform pressure distribution, but the manufacturing precision requirements increase
Solution Approach 1:
The axial position parameter of the suction ring groove is varied continuously or discretely in the circumferential direction, creating an asymmetric profile that adapts to local pressure conditions. This parameter variation is designed to be smooth and systematic, allowing for controlled manufacturing tolerances while achieving the desired flow control effect
Solution Approach 2:
The suction ring groove can be divided into multiple circumferential segments, each with its own optimized axial position. This segmentation approach allows for modular manufacturing and assembly, reducing the overall precision requirement compared to a completely custom asymmetric groove, while still achieving the pressure distribution compensation effect
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 configuration extends the stable operating range of the centrifugal compressor without degrading efficiency, effectively preventing fluid separation, stall, and surge, and allowing for a more stable operation across a broader flow rate range.
Implementation Method 1
a back-flow channel (9) to return fluid from a downstream position of an impeller full blade leading edge (6a) to an upstream position of the impeller full blade leading edge
Implementation Method 2
distribution in the circumferential direction of the axial-direction position of the suction ring groove or a width of the suction ring groove is asymmetric with reference to the rotational shaft
Data Source
Figure 1~2
Figure 3A~4
Figure 5A~5B
AI summary
A centrifugal compressor has a casing 7. In the casing 7 is formed a back-flow channel 9 to return fluid from a downstream position of an impeller full blade leading edge 6a to an upstream position of the impeller full blade leading edge 6a. The back-flow channel 9 includes a suction ring groove 9a and a back-flow ring groove 9b. The suction ring groove opens at the downstream position on the inner face 7a of the casing 7, and extends in the circumferential direction. The back-flow ring groove opens at the upstream position on the inner face 7a, and extends in the circumferential direction. Distribution in the circumferential direction of the axial-direction position of the suction ring groove 9a or a width of the suction ring groove 9a is asymmetric with reference to the rotation axis.