Why are most of the cooling fan blades odd?

Why are most of the cooling fan blades odd?

If you are good at observation, you will find that when cooling fan manufacturers design fans, the number of blades is mostly composed of 5, 7, 9, 11 and other odd blades. Why is the number of leaves odd rather than even?

This is because of the uneven quality of the material itself and the installation error, the blade will vibrate at high speed. If the blade is designed as an even number, due to the symmetry, the vibration of one side of the blade will be transmitted to the opposite blade, which is easy to cause resonance, resulting in increased noise and increased overall chatter. As a result, the blade can not bear resonance for a long time and fatigue, which may eventually lead to blade fracture; If the blades are designed in an odd number, although blade chatter also exists, there is no resonance with the blades, so noise and overall chatter can be effectively reduced.

Take the even number of blades as an example. Suppose that the blades of the cooling fan are even. When the blades on both sides are accurately balanced, the rotation of the blades is very stable. However, there are always errors in installation and manufacturing, especially the existence of installation gaps, which will cause one side of the fan to tilt slightly downward, and the other side of the fan to tilt upward under the action of leverage. When the fan rotates, the blades on both sides will form a resonance effect from top to bottom. If it is designed as an odd number of blades, although installation errors and clearances also exist, it is not easy to form resonance effects when rotating, which reduces the accuracy requirements of parts.

Therefore, compared with the number of odd and even blades, the odd blades do not need to worry about resonance when rotating at high speed, and the accuracy of the blades and the quality of the motor are reduced. Therefore, the odd blades use a very small cost, and achieve the effect that even blades can only achieve at a higher cost.