Centrifugal Compressor Diffuser Radius Variation for Recirculation Control
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Solution Overview
Problem
Centrifugal compressors experience significant losses due to recirculation flows near the tongue section, leading to inefficiencies and operational limitations, particularly at low flow rates, as the existing configurations fail to effectively suppress these recirculation flows.
Innovation Solution
The centrifugal compressor design incorporates a diffuser portion with a smaller outer radius in the angular range including the tongue section, shifting the flow passage cross-section inward, and a larger outer radius in the downstream range, facilitating the diffuser outlet flow to enter the radially inner side, thereby reducing recirculation and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the diffuser portion has a constant outer radius in all angular ranges, then the structure is simple and easy to manufacture, but recirculation flow occurs near the tongue section causing high loss
Solution Approach 1:
The diffuser portion is divided into a first diffuser portion in a first angular range including the tongue section with a smaller outer radius R1, and a second diffuser portion in a second angular range downstream with a larger outer radius R2. This local differentiation suppresses recirculation flow near the tongue section while maintaining overall structural functionality.
2Loss of energy
If the outer radius of the diffuser portion is increased in the first angular range including the tongue section, then the flow passage area is increased, but recirculation flow is generated causing separation and high loss
Solution Approach 1:
The first diffuser portion has a smaller outer radius R1 compared to the second diffuser portion's outer radius R2. This local reduction in radius prevents the flow passage connection part from being drawn into the flow too rapidly, suppressing separation and recirculation flow while maintaining adequate flow passage area downstream.
3Loss of energy
If the diffuser outlet flow is deflected toward the radially outer side, then the flow follows the scroll flow passage wall, but the recirculation flow enters the radially inner side region easily increasing loss
Solution Approach 1:
By setting the outer radius R1 of the first diffuser portion smaller than the outer radius R2 of the second diffuser portion, the flow passage cross-section is shifted inward in the first angular range. This creates a more favorable flow distribution that reduces the rate at which the main flow is drawn into the flow-passage connection part, suppressing recirculation flow entry into the radially inner side region.
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 recirculation flows, reduces losses, and improves surge characteristics, allowing for a wider operational range and increased efficiency by ensuring uniform energy distribution within the scroll flow passage.
Implementation Method 1
imparts kinetic energy to a fluid through rotation of an impeller and discharges the fluid outward in the radial direction, thereby achieving a pressure increase by utilizing the centrifugal force
Implementation Method 2
a diffuser part forming a diffuser flow passage for supplying the scroll flow passage with compressed air compressed by the impeller
Data Source
AI summary
A centrifugal compressor includes an impeller and a casing, the casing includes a scroll part forming a scroll flow passage and a diffuser part forming a diffuser flow passage. The diffuser part includes: a first diffuser portion belonging to a first angular range in a circumferential direction of the impeller; and a second diffuser portion belonging to a second angular range downstream of the first angular range in a flow direction of the scroll flow passage, of the angular range in the circumferential direction of the impeller, the second diffuser portion having an outer radius R2 which is defined along a reference circle centered at a rotational center of the impeller. An outer radius R1 of the first diffuser portion in the first angular range is smaller than the outer radius R2 of the second diffuser portion in the second angular range.