Impeller Blade Recess Geometry for Lower Secondary Flow Loss
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Solution Overview
Problem
Impellers in centrifugal compressors experience large blade loads from the hub to the tips, leading to efficiency losses due to secondary flow and leakage vortices, reducing the stable operating area and pressure ratio.
Innovation Solution
The impeller design features a recessed surface on the blades that curves convexly toward the rear, with increasing recess amount and curvature from the leading edge to the trailing edge, and a smaller midspan blade angle at the trailing edge, guiding secondary flow away from the tip and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the backward angle of the blades is decreased to increase the circumferential component of the absolute flow velocity at the outlet, then the pressure ratio is improved, but the blade load becomes uniformly large from the hub to the tips, resulting in large losses due to secondary flow and leakage vortices
Solution Approach 1:
The patent applies local quality by varying the blade angle along the span from hub to tip. Specifically, the blade angle is set to be smaller at the midspan and larger at the hub and tip regions. This local variation allows different parts of the blade to have optimized angles for their specific flow conditions, reducing secondary flow losses at the hub and tip while maintaining pressure ratio improvement from the reduced midspan angle.
Solution Approach 2:
The patent changes the blade angle parameter along the spanwise direction. By setting the blade angle at the midspan to be smaller than at the hub and tip, the patent creates a non-uniform parameter distribution that optimizes both pressure ratio and reduces energy losses. This parameter variation approach allows the blade to handle different flow conditions at different radial positions effectively.
2Stress or pressure
If the blade load is uniformly large from the hub to the tips, then the pressure ratio can be maintained, but the stable operating area is reduced and efficiency decreases
Solution Approach 1:
The patent uses local quality by implementing different blade angles in different spanwise regions. The hub and tip regions have larger blade angles to reduce secondary flow and improve stability, while the midspan has a smaller angle to maintain pressure ratio. This localized optimization ensures both pressure ratio and stable operating area are achieved simultaneously.
Solution Approach 2:
The patent segments the blade into three distinct regions along the span: hub region, midspan region, and tip region, each with different blade angles. This segmentation allows independent optimization of each region's performance characteristics, preventing the uniform blade angle design from causing either excessive losses or reduced stability.
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 design enhances the pressure ratio and efficiency of the centrifugal compressor by minimizing secondary flow and leakage, while maintaining load distribution.
Implementation Method 1
large losses due to flow structures such as secondary flow caused by the pressure gradient inside the impeller
Implementation Method 2
leakage vortices at the blade tips
Data Source
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AI summary
An impeller includes: a disk-shaped hub centered on an axis; and a plurality of blades arranged in a circumferential direction and protruding from a surface of the hub facing one side in a direction of the axis. In a cross-sectional view including a blade height direction which is a direction away from the hub toward a tip of each blade, the blade has a recessed surface curved convexly toward a rear side in a rotational direction. In the cross-sectional view, when a distance between an imaginary line connecting a tip-side edge and a hub-side edge of the blade and a midspan of the blade along a direction perpendicular to the imaginary line is defined as a recess amount, the blade has a portion where the recess amount increases from a leading edge side to a trailing edge side.