Air-Sending Device Blade Reflex and Bell Mouth Gap for Noise Reduction
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Solution Overview
Problem
Air-sending devices with ducted bell mouths fail to sufficiently mitigate noise caused by blade tip vortex due to the close proximity of the cylindrical part of the bell mouth and the outboard edge of the blade, leading to increased pressure fluctuations and noise.
Innovation Solution
An air-sending device with a propeller fan and a ducted bell mouth, where the blade inclination angle is negative in certain areas and the reflex angle is greater than or equal to 90 degrees in regions where the cylindrical part and the outboard edge face each other, reducing the interaction between the blade tip vortex and the bell mouth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a ducted bell mouth is used to surround the outboard area of the propeller fan, then the bell mouth structure is more complete and can guide airflow better, but the cylindrical part of the bell mouth comes too close to the outboard edge of the blade, causing blade tip vortex to interfere with the bell mouth and generate turbulence and noise
Solution Approach 1:
The patent applies local quality by introducing a gap between the cylindrical part of the bell mouth and the outboard edge of the blade specifically in the region where blade tip vortex occurs. This localized modification allows the bell mouth to maintain its airflow guiding function while preventing the harmful interaction between the blade tip vortex and the bell mouth structure, thereby reducing noise without compromising the overall bell mouth structure.
2Object-affected harmful factors
If the outboard part of each blade is bent toward the suction side to form a reflexed part, then noise from blade tip vortex is mitigated in semi-open bell mouth configurations, but this blade shape does not sufficiently reduce noise when used with a ducted bell mouth due to the close proximity of the cylindrical part and blade edge
Solution Approach 1:
The patent combines the reflexed part blade design with a localized gap configuration. The reflexed part bends the outboard portion of the blade toward the suction side to mitigate blade tip vortex, while the gap between the cylindrical part of the bell mouth and the blade edge provides additional noise reduction by preventing vortex-bell mouth interaction. This localized gap modification enhances the noise mitigation effect of the reflexed part without requiring significant changes to the overall blade length.
3Productivity
If the cylindrical part of the bell mouth is positioned close to the outboard edge of the blade, then the bell mouth can more effectively surround and guide the airflow, but the blade tip vortex interferes with the cylindrical part causing increased pressure fluctuations and noise
Solution Approach 1:
The patent introduces a localized gap between the cylindrical part of the bell mouth and the outboard edge of the blade in the region where blade tip vortex occurs. This gap prevents the blade tip vortex from directly interfering with the cylindrical part of the bell mouth, thereby reducing pressure fluctuations and noise. The gap is strategically positioned to maintain effective airflow guidance while eliminating the harmful vortex-bell mouth interaction.
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 length of the blade in the rotational axis direction, decreases the region where noise is generated, and mitigates turbulence and pressure fluctuations, effectively reducing noise caused by blade tip vortex.
Implementation Method 1
a propeller fan configured to rotate about a rotational axis
Implementation Method 2
Rotation of the propeller fan causes a leakage flow to occur near the outboard edge of each blade
Implementation Method 3
the blade inclination angle formed when the second straight line passes through the reflex point is defined as a first blade inclination angle; within an area where the position ratio is greater than or equal to at least 1, the first blade inclination angle has a negative value
Implementation Method 4
Rotation of the propeller fan causes a leakage flow to occur near the outboard edge of each blade of the propeller fan, whereby air flows from the pressure surface toward the suction surface. The leakage flow gives rise to a blade tip vortex near the suction surface.
Implementation Method 5
the flow of air in the vicinity of the outboard edge of the blade becomes turbulent
Implementation Method 6
a contraction part that gradually decreases in diameter in the direction of flow of an airflow generated by rotation of the propeller fan
Data Source
AI summary
An air-sending device includes a propeller fan to rotate about a rotational axis, and a ducted bell mouth surrounding an outboard area of the propeller fan. The propeller fan includes a plurality of blades. Each of the blades includes, in its outboard portion, a reflexed part bent upstream of an airflow that is generated in the direction of the rotational axis by rotation of the propeller fan. In the propeller fan, within an area that is closer to the trailing edge than is the near mid-chord area, the propeller fan is inclined downstream of the airflow from the inboard edge to the reflexed part. In at least a portion of an area where the cylindrical part of the bell mouth and the outboard edge of each blade face each, the reflexed part has a reflex angle of greater than or equal to 90 degrees.