Centrifugal Compressor Diffuser Retreating Surface Flow Separation
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Solution Overview
Problem
Multi-stage centrifugal compressors experience efficiency reduction due to fluid separation at wall surfaces, particularly when using open impellers with tip clearance, leading to uneven flow velocities and increased pressure loss.
Innovation Solution
Incorporating a retreating surface on the first diffuser wall surface and a projecting surface on the second diffuser wall surface, along with controlled inclinations and positions of outer wall surfaces, to reduce flow velocity differences and prevent separation, while optimizing the flow-path cross-sectional areas and shaft length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an open impeller is used to reduce manufacturing complexity and cost, then the impeller structure becomes simpler and easier to manufacture, but fluid separation occurs at the return channel wall surface due to uneven flow velocity distribution
Solution Approach 1:
The patent applies local quality by modifying only the first diffuser wall surface geometry (adding a retreating surface) rather than changing the entire impeller structure. This localized modification addresses the flow separation problem at the return channel while maintaining the open impeller design, thus preserving manufacturing ease while improving flow stability.
Solution Approach 2:
The patent changes the geometric parameters of the diffuser channel, specifically the inclination angle and shape of the first diffuser wall surface. By adjusting these parameters (creating a retreating surface with specific angle ranges), the flow velocity distribution is optimized to prevent separation, resolving the contradiction between simple impeller design and stable flow.
2Productivity
If the first diffuser wall surface has a steep inclination to increase flow velocity, then the compression efficiency improves, but fluid separation occurs at the return channel wall surface
Solution Approach 1:
The patent introduces a retreating surface with curved geometry on the first diffuser wall surface, replacing a straight inclination with a curved profile. This curvature allows gradual flow acceleration while preventing abrupt flow direction changes that cause separation, thus maintaining compression efficiency while improving flow stability.
Solution Approach 2:
The patent creates a dynamic flow path by designing the diffuser wall surface with varying inclination angles along the flow direction. The retreating surface provides a gradual, adaptive change in flow area and velocity, allowing the flow to adjust smoothly rather than experiencing sudden changes that would cause separation.
3Reliability
If the diffuser channel cross-sectional area is increased to reduce flow velocity and prevent separation, then the shaft length and axial dimensions increase
Solution Approach 1:
The patent solves the space constraint problem by changing the geometric configuration in the radial and circumferential dimensions rather than simply extending the axial dimension. The retreating surface design optimizes the cross-sectional area distribution in a way that prevents separation without requiring increased shaft length, effectively using dimensional optimization to resolve the contradiction.
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 reduces fluid separation, enhances efficiency, and minimizes shaft vibration and axial dimensions by ensuring proper flow turning and reducing pressure loss.
Implementation Method 1
The multi-stage centrifugal compressor provides pressure energy and velocity energy to a working fluid by rotating the impellers
Implementation Method 2
a diffuser channel for guiding a working fluid discharged from the impellers outward in a radial direction
Data Source
AI summary
A multi-stage centrifugal compressor according to at least one embodiment includes: multiple stages of impellers arranged in an axial direction; a casing surrounding the impellers; and a diffuser channel for guiding a working fluid discharged from the impellers outward in a radial direction. In a cross-section along the axial direction, a first diffuser wall surface on a hub side of a pair of diffuser wall surfaces that are opposed in the axial direction across the diffuser channel has a retreating surface retreating toward the hub side from a connection position with a downstream end of a first upstream wall surface to a radially outer side with respect to a tangential direction of the first upstream wall surface at the downstream end of the first upstream wall surface, the first upstream wall surface being positioned upstream of the first diffuser wall surface and connected to the first diffuser wall surface.