Cross Flow Fan Blade Radius Variation for Uniform Air Velocity
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Solution Overview
Problem
Existing cross flow fans face challenges in achieving low power input and low noise levels due to locally increased air velocity, which leads to energy loss and noise generation, as well as uneven air velocity distribution and flow separation, making it difficult to provide uniform air blowing and wide-range air distribution.
Innovation Solution
The design incorporates ring-shaped blade supporting members with blades arranged in a specific configuration, where the cross-sections of the blades have varying radii, with longer chord lengths in the central region and shorter chord lengths at the edges, to reduce maximum air velocity and prevent flow separation, resulting in a more uniform air velocity distribution and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blades have the same shape in cross-section in the width direction of the fan, then manufacturing is simplified, but air velocity becomes locally increased causing energy loss and noise
Solution Approach 1:
The patent applies local quality by varying the cross-sectional shape of blades along the width direction of the fan. Specifically, the outlet angle of blades is made different between the central part and both end parts in the width direction, creating locally optimized flow characteristics that reduce energy loss while maintaining manufacturing feasibility through systematic design variations.
2Productivity
If outlet angle is increased on the periphery of the fan, then ventilation resistance is controlled and air blowing positions are changed, but flow separation occurs causing increased energy loss and noise
Solution Approach 1:
The patent implements local quality by differentiating the outlet angles of blades in different radial positions. The central blades have one outlet angle configuration while the end blades have different outlet angles, optimizing each region's performance to achieve wide air distribution without causing flow separation and associated energy losses.
3Manufacturing precision
If outer diameter of the fan is increased, then air velocity distribution is uniformized, but flow leakage occurs and vibrations increase
Solution Approach 1:
The patent applies local quality by varying blade parameters (outlet angle and chord length) according to their position in the width direction rather than uniformly increasing the fan diameter. This localized optimization achieves uniform air velocity distribution while avoiding the harmful effects of flow leakage and vibrations associated with increased fan diameter.
4Manufacturing precision
If chord length is varied in the axial direction, then air velocity distribution in axial direction is uniformized, but blown air flow is concentrated to specific cascade of blades
Solution Approach 1:
The patent applies local quality by varying the outlet angle of blades in the width direction (circumferential direction) rather than varying chord length in the axial direction. This approach achieves uniform air velocity distribution while preventing concentration of blown air flow to specific blade cascades, thereby maintaining uniform air blowing in the circumferential direction.
Data Source
AI summary
A cross flow fan achieves low power input and low noise level by preventing flow separation on an air inlet side and reducing a maximum air velocity in the gap between the blades. At least one of units constituting a cross flow fan is an appearance unit configured such that when the unit is sequentially cut in a direction from one of rings to the other ring along a plane whose normal coincides with a rotation axis, a region S and a region C appear, the radius of a second circle, serving as an inner circumferencial circle (having a radius), in the region S being a first radius of predetermined length, the radius of the second circle, serving as the inner circumferencial circle, in the region C being a second radius shorter than the first radius.