Centrifugal Fan Blade Trailing Edge for Uniform Outlet Airflow
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Solution Overview
Problem
Centrifugal fans used in blowers experience variations in airflow velocity distribution at the blade outlet, leading to increased noise and deteriorated air blowing efficiency due to secondary flow vortices and boundary layer effects.
Innovation Solution
The centrifugal fan design incorporates a trailing edge with an inflection point and varying outlet angles at different locations along the edge, with specific angles adjusted to minimize airflow velocity variations by altering the work applied from the main plate and shroud regions, thereby uniforming the airflow distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the trailing edge has a constant outlet angle, then the blade structure is simple, but the airflow velocity distribution becomes non-uniform leading to increased noise and reduced efficiency
Solution Approach 1:
The trailing edge is designed with varying outlet angles at different axial positions, creating local quality variations that optimize airflow at each location. The outlet angle changes from the shroud side to the main plate side, allowing different regions of the blade to perform different functions in controlling the airflow, thereby achieving uniform velocity distribution and reducing noise.
2Speed
If the outlet angle is increased at the shroud side, then the airflow velocity at that region is accelerated, but the overall airflow uniformity deteriorates without proper coordination with other regions
Solution Approach 1:
The outlet angle parameter is varied continuously along the axial direction of the trailing edge. By changing the outlet angle from a first value at the shroud side to a second value at the main plate side, the airflow velocity is adjusted at different locations to achieve overall uniformity. This parameter variation compensates for boundary layer effects and ensures stable, uniform airflow composition.
3Object-generated harmful factors
If the trailing edge geometry is optimized for uniform airflow, then noise is reduced and efficiency improves, but the manufacturing complexity increases due to variable outlet angles
Solution Approach 1:
The trailing edge incorporates curved surfaces and continuous geometric transitions instead of straight lines and abrupt changes. The outlet angle varies smoothly along the axial direction, creating a curved profile that optimizes airflow while being manufacturable using standard forming techniques. This curvature approach balances performance optimization with manufacturing feasibility.
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 achieves a more uniform airflow velocity distribution, reducing noise and enhancing air blowing efficiency by accelerating or decelerating airflow as needed to match velocity across different regions.
Implementation Method 1
a centrifugal fan includes a shroud, a main plate and a plurality of blades... The plurality of blades are arranged at predetermined intervals in a rotational direction between the shroud and the main plate
Data Source
AI summary
In a centrifugal fan, a tangent line, which is tangent to a positive pressure surface of a blade and passes through a trailing edge of the blade, is defined as a first tangent line. A virtual circle is centered on a rotational axis and passes through the trailing edge. A tangent line, which is tangent to the virtual circle and passes through the trailing edge, is defined as a second tangent line. An angle, which is placed in front of the first tangent line in a rotational direction and is on an outer side of the virtual circle relative to the second tangent line, is defined as an outlet angle. When a change in the outlet angle is viewed at each of a plurality of locations along the trailing edge, the trailing edge has at least one inflection point.