Crossflow Fan Blade Dimples and Cutouts for Lower Noise and Power
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Solution Overview
Problem
Crossflow fans in air conditioners consume high drive power and do not adequately reduce noise, despite noise reduction techniques like cutouts in blades, as they do not effectively change the boundary layer flow to reduce resistance.
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 pressure resistance and drive power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected 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 blade is segmented into multiple regions: basic shape portions (non-cut portions) and cut portions (with cutouts). This segmentation allows different regions to serve different functions - the basic shape portions maintain structural integrity and produce less noise, while the cut portions reduce noise through the cutout configuration. The blade thickness varies between these regions, with cut portions having smaller thickness to further reduce noise.
Solution Approach 2:
Different regions of the blade are given different local properties. The basic shape portions maintain full thickness for structural strength, while cut portions have reduced thickness and include cutouts for noise reduction. The turbulent boundary layer controlling structure is selectively applied to specific regions (either basic shape portions or cut portions) to optimize the balance between noise reduction and drive power consumption.
Solution Approach 3:
The blade thickness parameter is changed between different regions - cut portions have smaller thickness than basic shape portions. Additionally, a turbulent boundary layer controlling structure is introduced to change the flow regime from laminar to turbulent in specific regions, which modifies the boundary layer characteristics and reduces pressure resistance, thereby reducing drive power while maintaining noise reduction benefits.
2Object-affected harmful factors
If simple cutout configuration is used, then noise is reduced, but pressure resistance is not sufficiently reduced
Solution Approach 1:
A turbulent boundary layer controlling structure is introduced to change the flow regime from laminar to turbulent. This parameter change in the boundary layer characteristics reduces pressure resistance by preventing flow separation and reducing the adverse pressure gradient effects. The controlling structure can be implemented as dimples, grooves, or rough surfaces on the blade surface.
Solution Approach 2:
The blade is divided into regions with different thicknesses and flow control characteristics. Cut portions have reduced thickness and include cutouts for noise reduction, while basic shape portions maintain full thickness. The turbulent boundary layer controlling structure is selectively applied to specific regions to optimize the balance between noise reduction and pressure resistance reduction.
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 drive power consumption by preventing gas separation from the blades, leading to improved efficiency and reduced motor input.
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
Implementation Method 2
changing a boundary layer from a laminar flow to a turbulent flow
Implementation Method 3
This allows gas flowing around the blade to enter the cutouts easily, thus breaking two dimensionality of the flow of gas on the negative pressure surface of the blade
Data Source
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.