Centrifugal Blower Shroud Ring Gap Segmentation

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Solution Overview

Problem

In centrifugal blowers, the minimum gap size between the shroud ring and the case at the radially inner end leads to increased backflow flow velocity, causing separation of the main flow from the shroud ring and generating noise.

Innovation Solution

A centrifugal blower design with a labyrinthine structure formed by a projection within a recess between the cover portion and the shroud ring, where the shortest distance between the radially inner end of the shroud ring and the cover portion is set to be larger than the shortest distance between the projection and the recess, reducing backflow velocity and preventing main flow separation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the gap size between the shroud ring and the case is reduced at the radially inner end to reduce backflow rate, then the backflow rate is reduced, but the backflow velocity increases causing main flow separation

Engineering Contradiction:

Improvebackflow rateVSAvoidbackflow velocity

Core Design Contradiction:

Quantity of substanceVSSpeed

Solution Approach 1:

The invention divides the gap region into two distinct zones: a first gap region with smaller gap size to reduce backflow rate, and a second gap region with larger gap size to control backflow velocity. This segmentation allows independent optimization of backflow quantity and velocity characteristics in different spatial zones.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention applies different gap size characteristics to different radial positions: the gap size decreases from the radially outer end toward the radially inner end in the first gap region, while the gap size increases from the radially inner end in the second gap region. This local quality variation optimizes flow control at different locations.

Inventive Principle:

Principle #3Local quality

2Quantity of substance

If the gap size is minimized at the radially inner end to reduce backflow, then backflow rate decreases, but noise increases due to high velocity discharge

Engineering Contradiction:

Improvebackflow rateVSAvoidnoise level

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The gap is segmented into a first gap region for backflow rate control and a second gap region for velocity control. The second gap region, located at the radially inner end, has an increased gap size that reduces the discharge velocity of backflow, thereby minimizing noise generation from high-velocity jet discharge.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention converts the potentially harmful high-velocity backflow discharge into a beneficial low-velocity discharge by increasing the gap size in the second gap region. This transforms the noise-generating high-speed jet into a quieter, lower-speed flow that merges smoothly with the main flow.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Quantity of substance

If the gap size is reduced from radially outer end to radially inner end to reduce backflow, then backflow rate decreases, but main flow separation occurs due to high backflow velocity

Engineering Contradiction:

Improvebackflow rateVSAvoidmain flow attachment

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The gap structure is divided into two regions with opposite gradient directions. The first gap region (radially outer to middle) has decreasing gap size to reduce backflow rate, while the second gap region (radially inner to middle) has increasing gap size to reduce backflow velocity, preventing main flow separation and maintaining flow stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different gap size distributions are applied to different radial zones. The outer region uses a converging gap to reduce backflow quantity, while the inner region uses a diverging gap to control backflow velocity and maintain main flow attachment to the shroud ring surface.

Inventive Principle:

Principle #3Local quality

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 effectively reduces the backflow rate and limits main flow separation from the shroud ring, enhancing flow rate performance and noise reduction.

Implementation Method 1

it is possible to increase a pressure loss at the time of passing the air through this gap

Methodology Applied

Scientific EffectPressure loss: Pressure Drop

Implementation Method 2

a centrifugal fan that is rotatable about a fan central axis to suction air in an axial direction of the fan central axis and discharge the suctioned air in a radial direction of the fan central axis

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Data Source

PatentUS11092162B2Centrifugal blower

Publication Date: 2021.08.17 DENSO CORP

AI summary

A centrifugal blower includes: a centrifugal fan, which includes a shroud ring; and a case. The case includes a cover portion that covers a surface of the shroud ring located on one side in an axial direction. The cover portion includes a recess formed in a cover opposing surface, which is opposed to the shroud ring, and the recess is shaped in a form of a circle. The shroud ring includes at least one projection that is formed in a ring opposing surface, which is opposed to the cover portion. A gap is formed between the cover portion and the shroud ring. A shortest distance between a radially inner end part of the shroud ring and the cover portion is set to be larger than a shortest distance between a surface of the projection and a surface of the recess.