Centrifugal Compressor Scroll Structure Reducing Flow Separation
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Solution Overview
Problem
Centrifugal compressors face efficiency losses due to recirculation flows causing separation from the scroll flow passage walls, particularly at low-flow operating points, which are not adequately addressed by existing solutions that reduce cross-sectional area, leading to excessive flow velocity and further losses.
Innovation Solution
A scroll structure with a connection region where the inner circumferential surfaces of the scroll start and end portions are connected, featuring a turning start point positioned at least 30% of the height dimension away from the turning end point along the axial direction at the minimum cross-sectional area, with a gradual change in direction to reduce fluid separation, and optionally incorporating a virtual inscribed circle or curved portions to slow down the direction change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the cross-sectional area of the flow passage connection section is decreased to suppress recirculation flow, then separation loss is reduced, but flow velocity becomes excessive and loss increases
Solution Approach 1:
The patent applies curvature by designing the inner circumferential surface in the connection region with a specific curved shape. The surface extends from the scroll end portion to the scroll start portion with a controlled turning angle, creating a smooth curved transition rather than a sharp angle. This curvature allows recirculation flow to follow the wall surface smoothly, preventing separation while maintaining adequate flow passage area and avoiding excessive flow velocity.
2Loss of energy
If the cross-sectional area of the flow passage connection section is decreased to suppress recirculation flow, then separation loss is reduced, but compressor efficiency in broad operational range decreases
Solution Approach 1:
The patent applies local quality by modifying only the specific connection region where the scroll end portion and scroll start portion intersect. The inner circumferential surface in this localized area is designed with a controlled turning angle relative to the axial direction, while the rest of the scroll flow passage maintains its conventional structure. This localized modification suppresses separation loss in the critical connection region without adversely affecting the overall compressor efficiency across the broad operational range.
3Loss of energy
If the turning angle of the inner circumferential surface is increased to suppress recirculation flow, then separation is reduced, but the direction change becomes too abrupt causing fluid separation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the turning angle of the inner circumferential surface in the connection region. The turning angle is set to be not less than 10 degrees and not more than 30 degrees relative to the axial direction. This parameter optimization ensures that the flow direction changes gradually enough to prevent fluid separation and maintain flow stability, while still effectively suppressing recirculation flow and reducing separation loss.
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 effectively suppresses separation losses across a broad operational range, enhancing efficiency by minimizing fluid separation when recirculating flows enter the scroll start portion, thereby improving the compressor's performance.
Implementation Method 1
the fluid flowing along the first inner circumferential surface is likely to separate from the second inner circumferential surface when flowing into the scroll start portion as the recirculation flow
Implementation Method 2
imparts kinetic energy to a fluid through rotation of an impeller and discharges the fluid radially outward, thereby achieving a pressure increase by utilizing the centrifugal force
Data Source
AI summary
A scroll structure of a centrifugal compressor includes, of a flow passage connection section where a scroll start portion and a scroll end portion of a scroll flow passage intersect, a connection region where a first inner circumferential surface of the scroll end portion in the centrifugal compressor and a second inner circumferential surface of the scroll start portion in the centrifugal compressor are connected. The connection region includes a turning start point where a direction starts to change from the first inner circumferential surface toward the second inner circumferential surface, and a turning end point where the change in direction from the first inner circumferential surface toward the second inner circumferential surface comes to an end. Where a cross-section orthogonal to an extension direction of a center line of the scroll flow passage in the connection region is a first cross-section, the turning start point on the first cross-section is a first turning start point, a turning end point on the first cross-section is a first turning end point, and a tangent line to the first inner circumferential surface passing through the first turning start point on the first cross-section is a first direction, the first turning start point exists at a position away from the first turning end point along the first direction by a distance not less than 30% of a height dimension along an axial direction of the centrifugal compressor at a minimum cross-sectional area position of the scroll flow passage.