Main causes of noise generated by axial flow fan

Axial flow fans and centrifugal fans are very common in use, and there are also some problems in use. Just like the axial flow fan, it will generate noise during use. What is the cause of the noise?

When the blade of axial flow fan is thin, sweeps forward too much, and the center of gravity deviates from the center of blade root section, the centrifugal force caused by high speed and the change of blade lift caused by instable inlet flow are easy to cause blade vibration. At the same time, due to fluid structure coupling, it may also lead to blade vibration, leading to blade fatigue damage in advance, reducing fan efficiency, and generating large aerodynamic noise.

The impeller modal vibration mode usually consists of different axial vibrations of four blades. The reason is usually that the stiffness of the forward swept blade is much less than that of the hub, that is, the blade is "soft" while the hub is "hard"; The low-frequency vibration type of the blade is mainly the overall torsion of the blade, while the high-frequency vibration type is mainly the bending wave of the blade. From the perspective of noise, the first six vibration types have a great impact. Because of the great influence of its swing on the flow field, the inlet angle of the blade changes, and finally the fluctuation of the blade surface lift is formed. In the most serious case, it will generate vibration, generate a lot of aerodynamic noise, and greatly reduce efficiency.

Understand the causes of noise generated by axial flow fan, and pay attention to reducing the noise during use.