Centrifugal Compressor Inlet Passage Narrowing for Surge Margin
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Solution Overview
Problem
Existing centrifugal compressors face challenges in improving surge margin and maintaining choked flow rate with complex structures, which are costly and space-intensive, particularly in compact turbochargers for automobiles.
Innovation Solution
A centrifugal compressor design featuring a narrowed inlet passage with a gradually inclined portion, where the constriction amount is between 0.01R1 and 0.1R1, and the flow passage area at the narrowed portion is equal to or larger than the throat area, to enhance surge margin without reducing the choked flow rate, along with a recirculation passage and annular guide vane for efficient air flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the outer diameter of the impeller is reduced to improve surge margin in low-flow-rate region, then the absolute velocity at the inlet increases and backflow is suppressed, but the throat area of the impeller section decreases resulting in reduced maximum flow rate
Solution Approach 1:
The invention applies local quality by creating a narrowed portion with specific dimensional characteristics (0.01R1≤σ≤0.1R1) at a specific location in the inlet passage. This localized geometric modification increases air velocity precisely where needed at the impeller inlet to suppress backflow, while the gradual expansion downstream ensures the throat area of the impeller section is not reduced, thereby maintaining maximum flow rate capability.
2Productivity
If the diameter of the tip (boss portion) of the hub is reduced to ensure choked flow rate, then the flow area is maintained, but the impeller cannot be properly fastened to the rotational shaft
Solution Approach 1:
The invention extracts the flow control function from the hub tip (boss portion) and relocates it to the inlet passage. By forming the narrowed portion in the inlet passage rather than reducing the hub tip diameter, the patent maintains both the choked flow rate (through the controlled narrowing) and the fastening capability (by preserving the hub tip dimensions needed for mechanical attachment).
3Reliability
If a secondary passage with open/close valve is added to bypass the narrowed portion, then both surge margin improvement and choked flow rate are ensured, but the structure becomes complicated increasing cost and space
Solution Approach 1:
The invention applies self-service by designing the inlet passage geometry to automatically provide both surge margin improvement and choked flow rate assurance without requiring external control mechanisms. The narrowed portion with gradual expansion creates a flow conditioning effect that self-regulates across different operating conditions, eliminating the need for secondary passages, valves, and control systems.
4Reliability
If a narrowed portion with large constriction amount is provided in the inlet passage to improve surge margin, then the intake air velocity increases, but the choked flow rate is reduced
Solution Approach 1:
The invention applies parameter changes by precisely controlling the constriction amount σ within the range 0.01R1≤σ≤0.1R1 and managing the gradual expansion geometry (where distance from rotational axis increases toward blade tips). This parameter optimization allows the narrowed portion to increase velocity for surge margin improvement while the controlled expansion prevents excessive flow area reduction, thereby maintaining choked flow rate.
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 effectively suppresses backflow and improves surge margin while maintaining choked flow rate, offering a simpler and more cost-effective solution for compact turbochargers.
Implementation Method 1
narrowing is provided in an inlet passage, through which intake air flows to the impeller, to increase the intake air velocity at the inlet of the impeller
Implementation Method 2
a centrifugal compressor according to the present invention comprises: an impeller including a hub and a plurality of blades disposed on an outer peripheral surface of the hub
Data Source
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AI summary
A centrifugal compressor includes an impeller including a hub and a plurality of blades disposed on an outer peripheral surface of the hub at intervals in a circumferential direction, and a casing accommodating the impeller and defining an inlet passage for introducing air along an axial direction of the impeller. An inner peripheral surface of the inlet passage includes a narrowed portion, and an inclined portion connected to a downstream side of the narrowed portion and having a radial distance from a rotational axis of the impeller gradually increasing toward the vicinity of tips of leading edges of the blades. Further, 0.01R1≤σ≤0.1R1 is satisfied, where R1 is radial distance between a downstream end of the inclined portion and the rotational axis, R2 is radial distance between a downstream end of the narrowed portion and the rotational axis, and σ is constriction amount which is a difference between R1 and R2.