Centrifugal Compressor Return Flow Passage Noise Reduction
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Solution Overview
Problem
In centrifugal compressors with return flow passages, the circulation of air from the downstream to the upstream can disturb the main air flow, leading to noise issues and reduced quietness, especially during operational conditions that cause surges.
Innovation Solution
A turbocharger design with a return flow passage that incorporates a diameter-reducing portion and a ring-shaped passage to deflect and merge the circulated air with the main flow, minimizing interference and disturbance, thereby reducing noise and suppressing surges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return flow passage is provided to suppress surges, then surge suppression capability is improved, but noise increases due to disturbance of the main flow
Solution Approach 1:
A diameter-reducing portion is introduced as an intermediary component in the return flow passage to decelerate the circulated air before it merges with the main flow. This mediator structure reduces the velocity of the return flow, preventing disturbance to the main air flow while maintaining surge suppression capability.
Solution Approach 2:
The cross-sectional area of the return flow passage is reduced at a specific portion, changing the flow parameters (velocity, pressure) of the circulated air. This parameter change decelerates the return flow to a level that does not disturb the main flow, thereby reducing noise while maintaining the surge suppression function.
2Reliability
If air is circulated from downstream to upstream through the return flow passage, then surge is suppressed, but flow stability deteriorates due to interference with the main flow
Solution Approach 1:
The diameter-reducing portion serves as a flow conditioning intermediary that stabilizes the return flow before it rejoins the main flow. By controlling the geometry of this intermediate section, the circulated air is decelerated and its flow characteristics are modified to match the main flow, preventing instability and interference.
Solution Approach 2:
By changing the cross-sectional area parameter along the return flow passage, the flow velocity and pressure parameters of the circulated air are adjusted. This parameter modification ensures that when the return flow merges with the main flow, the combined flow remains stable without causing disturbances or oscillations.
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
The design improves quietness and extends the range of flow rates where surges are suppressed by ensuring the circulated air merges with the main flow without disturbing it, reducing noise and maintaining flow stability.
Implementation Method 1
a diameter-reducing portion decelerating the circulated air
Implementation Method 2
air is compressed along with rotation of the compressor wheel
Data Source
Figure 1~2
Figure 3~4(b)
Figure 5
AI summary
A centrifugal compressor includes a housing (6) that accommodates a wheel (10). The housing (6) includes an air intake space (11) formed on an entrance side of the wheel (10); a flow passage (14) to guide fluid compressed by the wheel (10) to the outside of the housing (6); a return flow passage (22) opened on each wall surface of the air intake space (11) and the flow passage (14) to circulate a part of the fluid in the flow passage (14) to the air intake space (11) without passing through the wheel (10); and an introduction portion (24) provided in the air intake space (11), and having an inner peripheral surface (24c) that forms a flow passage to guide the fluid from the outside of the housing (6) to the wheel (10). A downstream end (24b) of the inner peripheral surface (24c) in a flowing direction of the fluid is located inside in the radial direction of a shaft (8) than the wall surface of the housing (6) on which the return flow passage (22) is opened.