Crossflow Fan Blade Notches That Cut Noise Without Added Drag
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Solution Overview
Problem
Crossflow fans with notches on the blade edges reduce noise but increase air resistance, necessitating higher power output from the electric motor to maintain sufficient air discharge volume.
Innovation Solution
A crossflow fan design featuring blades with notches at either the inner or outer edges, or both, arranged at predetermined intervals, and grooves that reduce blade thickness at notch bottoms, along with a turbulent boundary layer control structure, to minimize collision loss and noise while maintaining efficient airflow.
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 impeller rotation increases
Solution Approach 1:
The patent applies local quality by making the blade thickness non-uniform: the blade thickness at the bottom of each notch is made smaller than the blade thickness of the basic shape section. This localized thinning at specific positions (notch bottoms) allows the blade to reduce noise through notch formation while minimizing the overall air resistance increase that would occur with uniform blade modifications.
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 region increases
Solution Approach 1:
The invention applies local quality by locally reducing blade thickness only at the bottom regions of the notches, while maintaining the basic blade shape and thickness in other areas. This localized modification reduces trailing vortices at the outlet region where notches are present, while minimizing interference with the inlet region airflow, thus reducing collision loss compared to more extensive blade modifications.
3Loss of energy
If blade thickness at notch bottom is reduced, then collision loss is minimized, but blade strength may be compromised
Solution Approach 1:
The patent applies local quality by reducing blade thickness only at the bottom of each notch, which is the specific location where collision loss occurs during rotation. The rest of the blade maintains its original thickness and structural integrity. This localized thinning minimizes collision loss at the critical notch bottom region while preserving the overall strength of the blade through maintaining adequate thickness in the basic shape sections.
Solution Approach 2:
The invention applies preliminary action by pre-forming the notches with controlled bottom thickness during blade manufacturing. This preliminary structuring of the blade geometry ensures that the reduced thickness at notch bottoms is built-in from the start, allowing the blade to operate with minimized collision loss while maintaining sufficient strength through the designed basic shape sections that provide structural support.
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 effectively reduces noise and power output requirements for the electric motor by minimizing collision loss and airflow disturbance, allowing for smoother airflow and reduced energy consumption.
Implementation Method 1
A plurality of grooves are formed on one of the positive pressure surface and the negative pressure surface so that a blade thickness in the vicinity of the bottom of each notch is less than the blade thickness of the adjacent basic shape section
Implementation Method 2
A plurality of notches are formed at at least one of the inner edge and the outer edge of each blade... A plurality of grooves are formed on one of the positive pressure surface and the negative pressure surface so that a blade thickness in the vicinity of the bottom of each notch is less than the blade thickness of the adjacent basic shape section
Data Source
Figure 1
Figure 2
Figure 3(a)~4
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.