Multiblade Centrifugal Blower Asymmetric Blade Noise Reduction
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Solution Overview
Problem
Conventional multiblade centrifugal blowers face performance deterioration due to reduced spatial volume and secondary flow effects, which hinder noise reduction and blowing performance.
Innovation Solution
A multiblade centrifugal blower design featuring a centrifugal fan with curved rectangular blades and a scroll casing with a bell mouth, where the length of the outer blade edge is shorter than the inner edge, minimizing interference and secondary flow, and optimizing the bell mouth's position to reduce noise without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a rectifying rib is arranged near the tongue formed in the scroll casing to guide reverse flow air, then noise is reduced, but the spatial volume inside the scroll casing is reduced and blowing performance deteriorates
Solution Approach 1:
The patent removes the rectifying rib structure from the scroll casing that was previously used to guide reverse flow air. Instead, it extracts the noise reduction function to the blade design itself through asymmetric geometry, thereby eliminating the harmful volume reduction while maintaining noise control
Solution Approach 2:
The patent applies asymmetry to the blade cross-section with different lengths (B1 > B2), creating an asymmetric airflow guidance that naturally directs reverse flow without requiring additional rectifying structures, thus avoiding volume loss in the scroll casing
2Object-affected harmful factors
If a bell mouth is arranged circumjacent to the air inlet to reduce noise, then noise is reduced, but the effective volume of the scroll casing is reduced and blowing performance deteriorates
Solution Approach 1:
The patent employs asymmetric blade geometry where the inner edge length B1 is greater than the outer edge length B2. This asymmetry creates optimized airflow patterns that reduce noise without requiring a traditional bell mouth structure, thereby preserving the effective volume of the scroll casing
Solution Approach 2:
The patent applies local quality optimization at the blade tips with different lengths (B1 and B2) to achieve noise reduction specifically at the air inlet region, while leaving the rest of the scroll casing volume intact and functional
3Productivity
If air flows towards the hub due to inertial force, then air is sucked into the centrifugal fan, but reverse flow is created between blades that blocks the main flow and creates secondary flow along the inner wall
Solution Approach 1:
The patent uses asymmetric blade geometry with inner edge length B1 greater than outer edge length B2 to create differential airflow guidance. This asymmetry directs the inertially-driven air flow more effectively toward the hub while minimizing reverse flow between blades and secondary flow along the inner wall, thus maintaining air suction performance while reducing harmful flow patterns
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 reduces noise and maintains blowing performance by minimizing blade interference and secondary flow, achieving a noise reduction of approximately -1 dB without deteriorating the blower's performance.
Implementation Method 1
When air is sucked into a cylindrical basket-shaped centrifugal fan of a multiblade centrifugal blower, because inertial force acts on the sucked-in air, the sucked-in air flows towards the hub of the centrifugal fan.
Implementation Method 2
rotation of the centrifugal fan causes suction of air from an opening on the front side of the hub toward a direction of a rotating shaft of the motor, and causes discharge of the air through a space between the blades in a centrifugal direction
Data Source
AI summary
A multiblade centrifugal blower includes a centrifugal fan including a hub rotated by a motor, and plural curved rectangular blades arranged at predetermined intervals in a circumferential direction of the hub forming a cylindrical basket with an opening on a front side of the hub, and a scroll casing including an air inlet and an air outlet, and houses the centrifugal fan inside to face the air inlet. A length from a rear end to an front end of an outer edge of the blade is shorter than a length from a rear end to an front end of an inner edge of the blade, and a bell mouth is configured such that distance between a tip part of the inner edge of the blade and an inner wall of the scroll casing is the minimum at an inner tip part P of the bell mouth of the air inlet.