Multi-blade Fan Blade Angle Optimization for Noise Reduction
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Solution Overview
Problem
Multi-blade fans for air-cooled engines are less efficient and noisier than turbofans, with conventional noise reduction methods increasing component count and cost, and reducing the number of blades lowers air volume while increasing noise frequency.
Innovation Solution
A multi-blade fan design with an impeller having a sum of inlet and outlet angles less than 80°, reduced number of blades, and optimized blade geometry to maintain air volume while reducing noise levels, including specific angle definitions and blade counts to minimize noise and maximize air volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the number of blades is reduced to lower rotational noise frequency, then noise level is improved, but air volume is lowered
Solution Approach 1:
The patent changes the geometric parameters of the blades, specifically setting the sum of the inlet angle β1 and the angle β′2 (where β′2 = 180° - β2) to less than 80°. This parameter optimization allows the fan to maintain high air volume while using fewer blades, thereby reducing rotational noise frequency without sacrificing productivity
Solution Approach 2:
The patent optimizes the dynamic characteristics of the blade geometry to improve aerodynamic efficiency. By carefully selecting the inlet and outlet angles, the blade design achieves better flow control and reduces turbulence, allowing fewer blades to move more air efficiently while generating less noise
2Productivity
If the speed of rotation is raised to increase air volume, then air volume is improved, but rotational noise frequency increases
Solution Approach 1:
Instead of increasing speed to boost air volume, the patent changes the blade angle parameters (inlet angle β1 and outlet angle β2) to optimize performance at the existing rotation speed. The condition that the sum of β1 and β′2 is less than 80° enables the fan to achieve high air volume without increasing rotational speed, thereby avoiding increased noise frequency
3Object-generated harmful factors
If acoustic material is added to the impeller cover to reduce noise, then noise level is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the noise reduction function from the impeller cover assembly and relocates it to the blade geometry itself. By optimizing the blade angles to reduce noise at the source, the design eliminates the need for additional acoustic materials or sound insulation components, thereby reducing device complexity and cost while maintaining noise control
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 achieves a 2 dB(A) reduction in noise level and maintains air volume, improving auditory sensation and fan efficiency while reducing the number of blades and noise frequency, with enhanced air volume and noise reduction compared to prior art.
Implementation Method 1
a multi-blade fan (sirocco fan) that forcefully blows cooling air onto an engine by rotating an impeller having many forward-curved blades
Implementation Method 2
blows air by rotating an impeller having many forward-curved blades
Data Source
AI summary
In a multi-blade fan for an air-cooled engine, by defining the inlet angle β1 and the angle β′2 to make the sum thereof less than 80° (preferably defining β1 as 32° and β′2 as 36°), the multi-blade fan achieves greater air volume than in the case where the sum is made 80° or greater, where β1 is the angle between the relative velocity direction and the peripheral direction on the inlet side of the blades, β2 is the angle between the relative velocity direction and the peripheral direction on the outlet side of the blades, and β′2 is the difference obtained by subtracting β2 from 180°. The number of blades can therefore be reduced to realize lower noise level while still maintaining the same air volume as the prior art multi-blade fan.