Centrifugal Compressor Diffuser Hub Convex Portion
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Solution Overview
Problem
In centrifugal compressors, reverse flow at the hub wall surface in the diffuser flow path leads to reduced efficiency, increased pressure loss, and a decline in surge margin, limiting the operational range and efficiency of turbochargers.
Innovation Solution
A centrifugal compressor design featuring a hub-side convex portion on the hub wall surface that protrudes towards the shroud wall surface, reducing the thickness of the boundary layer and preventing reverse flow, combined with a shroud-side concave portion to maintain flow path width and uniformity, enhancing the deceleration and pressure recovery efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the diffuser flow path is designed with conventional smooth walls, then the structure is simple and easy to manufacture, but reverse flow occurs at the hub wall surface side leading to reduced efficiency and increased pressure loss
Solution Approach 1:
The hub wall surface is modified with a convex portion that protrudes radially outward, creating a localized structural change only where reverse flow occurs. This local modification prevents reverse flow and reduces pressure loss without requiring complete redesign of the entire diffuser structure, thus maintaining ease of manufacture while improving energy efficiency.
2Reliability
If the diffuser flow path width is reduced to prevent reverse flow, then reverse flow is prevented, but the flow velocity cannot be sufficiently reduced and pressure recovery is compromised
Solution Approach 1:
The convex portion is positioned specifically at the hub wall surface where reverse flow occurs, creating a localized narrowing that prevents reverse flow without excessively reducing the overall flow path width. This allows the diffuser to maintain both reverse flow prevention and adequate pressure recovery capability.
Solution Approach 2:
Instead of reducing the axial or radial width of the diffuser flow path, the invention modifies the flow path in the circumferential dimension by adding a convex portion that protrudes radially outward. This dimensional approach prevents reverse flow while preserving the overall flow path width necessary for pressure recovery.
3Adaptability or versatility
If the flow rate is reduced to expand surge margin, then the compressor can operate at lower flow rates, but reverse flow occurs more readily at low flow rates reducing efficiency
Solution Approach 1:
The convex portion on the hub wall surface is designed in advance to counteract the reverse flow tendency that occurs at low flow rates. By pre-positioning this anti-reverse flow structure, the diffuser can maintain efficient flow patterns even when operating at reduced flow rates, thus enabling surge margin expansion without significant efficiency loss.
Data Source
AI summary
A centrifugal compressor 10 includes a diffuser 13 that comprises: a shroud wall surface 131 that extends in the radial direction of a rotating shaft 3; and a hub wall surface 132 that extends in the radial direction and opposes the shroud wall surface 131 on the downstream side of a flow in the axial direction of the rotating shaft 3, the hub wall surface having a gap between itself and the shroud wall surface 131, and with that gap, forming an annular diffuser flow path 130 through which a fluid flows. A hub-side convex portion 132b is formed over the entire periphery of the hub wall surface 132, the hub-side convex portion 132b protruding toward the shroud wall surface 131 side relative to a straight line L1 that connects a starting end 132s on an inlet 130a side of the diffuser flow path 130 and a terminating end 132e on an outlet 130b side of the diffuser flow path 130.