Scroll Casing Asymmetric Cross-Section for Centrifugal Compressor Flow Control
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Solution Overview
Problem
Centrifugal compressors experience significant losses due to recirculation flows at the tongue section, leading to separation and reduced efficiency, particularly at low flow-rate operation points, as existing designs fail to effectively suppress recirculation flows.
Innovation Solution
The scroll casing is designed with a separation suppressing cross section that adjusts the flow line curvature of recirculation flows by positioning the inner end of the scroll flow passage on the inner side radially and the middle point of maximum height on the back side axially, with a curved surface protruding towards the center, allowing for gradual changes in flow line curvature from the connection position to a predetermined angular position, thereby reducing rapid changes and separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the scroll flow passage has a circular cross-sectional shape over the entire region, then the structure is simple and easy to manufacture, but recirculation flow causes rapid change in flow line curvature leading to separation and high loss
Solution Approach 1:
The patent applies local quality by changing the cross-sectional shape of the scroll flow passage only in specific regions where recirculation flow occurs. The non-circular cross-section with the inner end positioned on the back side of the middle point is implemented in the region from the connection position to the predetermined angular position upstream, while other regions may maintain simpler shapes. This localized modification addresses the separation problem without requiring complex geometry throughout the entire passage.
Solution Approach 2:
The patent employs asymmetry by positioning the inner end of the scroll flow passage on the back side of the middle point in the axial direction. This creates an asymmetric cross-sectional shape that is specifically designed to control the flow line curvature of recirculation flow. The asymmetric geometry gradually changes the flow line curvature, preventing rapid changes that cause separation, while maintaining manufacturing feasibility.
2Device complexity
If the inner end of the scroll flow passage is positioned at the middle point in the axial direction, then the structure is simplified, but recirculation flow experiences rapid change in flow line curvature causing separation
Solution Approach 1:
The patent applies local quality by changing the cross-sectional shape of the scroll flow passage only in specific regions where recirculation flow occurs. The non-circular cross-section with the inner end positioned on the back side of the middle point is implemented in the region from the connection position to the predetermined angular position upstream, while other regions may maintain simpler shapes. This localized modification addresses the separation problem without requiring complex geometry throughout the entire passage.
Solution Approach 2:
The patent employs asymmetry by positioning the inner end of the scroll flow passage on the back side of the middle point in the axial direction. This creates an asymmetric cross-sectional shape that is specifically designed to control the flow line curvature of recirculation flow. The asymmetric geometry gradually changes the flow line curvature, preventing rapid changes that cause separation, while maintaining manufacturing feasibility.
3Loss of energy
If the scroll flow passage has a non-circular cross-sectional shape to suppress recirculation flow, then separation is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by changing the cross-sectional shape of the scroll flow passage only in specific regions where recirculation flow occurs. The non-circular cross-section with the inner end positioned on the back side of the middle point is implemented in the region from the connection position to the predetermined angular position upstream, while other regions may maintain simpler shapes. This localized modification addresses the separation problem without requiring complex geometry throughout the entire passage.
Solution Approach 2:
The patent employs asymmetry by positioning the inner end of the scroll flow passage on the back side of the middle point in the axial direction. This creates an asymmetric cross-sectional shape that is specifically designed to control the flow line curvature of recirculation flow. The asymmetric geometry gradually changes the flow line curvature, preventing rapid changes that cause separation, while maintaining manufacturing feasibility.
Data Source
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AI summary
A scroll casing forms a scroll flow passage of a centrifugal compressor, and provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in the axial direction of the centrifugal compressor, the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end.