Axial Flow Fan Blade Segmentation for Stress Reduction
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Solution Overview
Problem
Existing axial flow fans face challenges in increasing chord length for better air-blowing and noise characteristics while ensuring blade strength, as longer chord lengths lead to stress concentration and difficulties in molding due to uneven cooling and shrinkage, especially when trying to separate blades for die removal.
Innovation Solution
The axial flow fan design includes a boss portion with rotor blades segmented into two areas, where the forward sweep angle varies quadratically in the first area and linearly in the second area, and the chord-pitch ratio increases curvilinearly from a minimum value in the first area and linearly in the second area, reducing stress concentration and allowing for sufficient blade separation during molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the chord length of the rotor blade is increased to improve air-blowing and noise characteristics, then the air capacity and noise reduction are improved, but stress concentration occurs at the base of the leading edge and blade strength is compromised
Solution Approach 1:
The patent applies local quality by varying the plate thickness specifically at the base of the leading edge (stress-concentrating part) while maintaining uniform thickness in other blade regions. This localized thickness increase (making the base portion thicker than the middle portion) directly addresses stress concentration at the critical location without unnecessarily increasing overall blade mass or complexity.
2Strength
If the plate thickness of the base portion is locally increased to enhance blade strength, then the blade can withstand wind drifts and gusts, but discontinuity in plate thickness during molding causes uneven cooling and shrinkage leading to blade contortion
Solution Approach 1:
The patent applies parameter changes by carefully controlling the plate thickness transition in the stress-concentrating part. The thickness varies gradually from the base toward the middle of the blade, creating a smooth gradient rather than an abrupt change. This gradual parameter transition allows the molded blade to maintain uniform cooling and shrinkage characteristics during manufacturing, preventing contortion while still providing the necessary strength enhancement at the base portion.
3Ease of manufacture
If the rotor blades are molded integrally to reduce manufacturing complexity, then production efficiency is improved, but blades cannot be separated sufficiently far apart for die removal
Solution Approach 1:
The patent applies dimensionality change by extending part of the leading edge portion of the vane closer to the boss portion than an arbitrary point on the leading edge portion, in the rotation direction. This creates a stepped configuration where the blade base portions are separated sufficiently in the radial dimension to allow die removal, while maintaining integral molding for manufacturing efficiency.
Data Source
AI summary
An axial flow fan improves air capacity and static pressure characteristics, and can ease stress at a leading edge portion of a blade base, even when a shape for noise reduction is adopted. An axial flow fan includes a boss portion and rotor blades. A rotor blade is segmented into a first area extending from the boss portion toward the outer peripheral side, and a second area connected to the first area and extending from the first area to the outermost periphery of the rotor blade. The distribution of a forward sweep angle varies quadratically in the first area, and the maximum forward sweep angle in the first area is not larger than the forward sweep angle in the second area. The distribution of chord-pitch ratio varies in a curved manner from the base as the minimum value in the first area, and is linear in the second area.