Crossflow Fan Blade with Dimples to Reduce Drive Power and Noise
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Solution Overview
Problem
Existing crossflow fans consume high drive power and fail to adequately reduce noise, despite previous attempts to minimize noise through blade modifications.
Innovation Solution
A crossflow fan design featuring curved blades with cutouts and a turbulent boundary layer controlling structure, such as dimples, that changes the boundary layer from laminar to turbulent flow, reducing resistance and drive power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If cutouts are formed in the outer peripheral edge of the blade, then noise is reduced, but drive power cannot be reduced sufficiently
Solution Approach 1:
The invention applies different structural features to different parts of the blade: cutouts are formed in the outer peripheral edge to reduce noise, while a turbulent boundary layer controlling structure (such as dimples or grooves) is formed in the negative pressure surface to reduce drive power. This local differentiation of blade properties resolves the contradiction between noise reduction and power consumption reduction.
Solution Approach 2:
The blade is segmented into multiple functional zones: the outer peripheral edge with cutouts for noise reduction, the negative pressure surface with turbulent boundary layer controlling structures for power reduction, and the basic blade structure for airflow generation. This segmentation allows each zone to independently address specific performance requirements.
2Use of energy by moving object
If a turbulent boundary layer controlling structure is formed in the negative pressure surface, then drive power is reduced, but blade structure becomes more complex
Solution Approach 1:
The invention changes the surface parameters of the blade by forming turbulent boundary layer controlling structures (dimples, grooves, or rough surfaces) in the negative pressure surface. This modifies the boundary layer flow characteristics from laminar to turbulent, reducing flow separation and decreasing the resistance acting on the blade, thereby reducing drive power despite increased structural complexity.
3Object-generated harmful factors
If multiple cutouts are formed in the peripheral edge, then noise is reduced, but gas flow separation increases
Solution Approach 1:
The turbulent boundary layer controlling structure in the negative pressure surface acts as a preliminary anti-action measure. By inducing turbulence upstream of the cutouts, it strengthens the boundary layer's resistance to separation, counteracting the potential harmful effect of cutouts on flow attachment and maintaining reliable gas flow along the blade surface.
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 drive power and noise by preventing gas separation from the blades, leading to improved airflow efficiency and lower motor input requirements.
Implementation Method 1
A turbulent boundary layer controlling structure that prevents a gas flowing around the blade from separating from the blade by changing a boundary layer from a laminar flow to a turbulent flow is formed in a negative pressure surface of the blade
Implementation Method 2
A turbulent boundary layer controlling structure that prevents a gas flowing around the blade from separating from the blade
Implementation Method 3
JP2006125390 (A) discloses a blade having a plurality of cutouts that are formed in the outer periphery of the blade and spaced apart at predetermined intervals to reduce noise produced by a fan
Data Source
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AI summary
A crossflow fan includes a rotary impeller formed by curved blades 42. Each of the blades 42 has an outer peripheral edge 43 close to the centrifugal side of the impeller and an inner peripheral edge 44 close to the rotation axis side of the impeller. A plurality of cutouts 45 are formed in the outer peripheral edge 43 and spaced apart at predetermined intervals. Dimples 48 for changing a boundary layer from a laminar flow to a turbulent flow are formed in a negative pressure surface 4q of each blade 42 in the vicinity of the outer peripheral edge 43 to prevent the gas flowing around the blade 42 from separating from the blade 42.