Cross-Flow Fan Blade Notches With Lower Air Resistance
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Solution Overview
Problem
Crossflow fans with notches to reduce noise increase air resistance, necessitating higher power output from electric motors to maintain sufficient air discharge volume.
Innovation Solution
The design incorporates notches at the inner or outer edges of blades with varying blade thickness and grooves that gradually change thickness, reducing collision loss and noise while maintaining efficient air flow, and optionally includes a turbulent boundary layer control structure like dimples to prevent air separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If notches are formed at the outer edge of each blade to reduce noise, then noise is reduced, but air resistance against rotation increases
Solution Approach 1:
The blade thickness is made non-uniform by forming notches at specific locations (outer edge or inner edge) rather than modifying the entire blade. This localized modification reduces noise at the trailing edge while minimizing the impact on overall air resistance, as only specific portions of the blade are altered rather than the whole structure.
Solution Approach 2:
The blade is segmented into different thickness regions through the formation of notches, creating distinct zones: a first thickness region at the notch location and a second thickness region at other locations. This segmentation allows the blade to reduce noise through the thinner notch portions while maintaining sufficient thickness in other areas to minimize air resistance.
2Object-generated harmful factors
If notches are formed at the outer edge of each blade, then trailing vortices are reduced, but collision loss at the inlet increases
Solution Approach 1:
Instead of forming notches only at the outer edge of the blade (conventional approach), the invention provides the alternative of forming notches at the inner edge of the blade. This inverted approach shifts the location of the thinner region to where it less interferes with incoming air flow, thereby reducing collision loss while still achieving trailing vortex reduction through the notch structure.
Solution Approach 2:
The notch formation creates a localized thin region at either the outer or inner edge, allowing the blade to address trailing vortex issues locally without significantly affecting the overall air flow characteristics and collision loss at the inlet.
3Loss of energy
If blade thickness at the notch bottom is reduced, then collision loss is reduced, but structural strength may be compromised
Solution Approach 1:
The blade employs non-uniform thickness distribution with thinner regions at the notch locations and thicker regions at other locations. This local quality variation reduces collision loss at the inlet while maintaining sufficient structural strength in the thicker portions of the blade to compensate for the weakened notch areas.
Solution Approach 2:
The blade structure is segmented into different thickness zones, creating a first thickness region at the notch bottom and a second thickness region at other locations. This segmentation allows the blade to optimize performance by having thinner sections where collision occurs and thicker sections where structural integrity is critical.
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 configuration reduces the power output required from the electric motor while effectively minimizing noise and air resistance, enhancing the efficiency of the crossflow fan operation.
Implementation Method 1
The notches 42b, which are formed in the blade 42 as described above, reduce trailing vortices (not shown) generated at an outlet region M of a crossflow fan 204.
Implementation Method 2
since the blade thickness in the vicinity of the bottom of each notch is less than the blade thickness of the adjacent basic shape section, collision loss at the entry of air flow into the notch is reduced
Implementation Method 3
A turbulent boundary layer control structure is provided on the negative pressure surface of each blade, which changes a boundary layer of air flow from laminar flow to turbulent flow, thereby preventing air flowing onto the blade from separating from the blade
Data Source
AI summary
A crossflow fan includes an impeller formed by plate-like blades 42. Each blade 42 is inclined such that the outer edge 42a is located on the leading side of the inner edge 42d with respect to the rotation direction of the impeller 41. The face of each blade 42 that is located on the leading side of the rotation direction forms a positive pressure surface 42p, and a face located on the trailing side forms a negative pressure surface 42q. Notches 42b are formed at the outer edge 42a of the blade 42. The notches 42b are arranged at predetermined intervals along the rotation axis of the impeller. A basic shape section 42c is formed between each adjacent pair of the notches 42b. The blade thickness L2 in the vicinity of the bottom 42y of each notch 42b is smaller than the blade thickness of the basic shape section 42c adjacent to the notch 42b.