The main reason of noise produced by axial fan

Axial fan, centrifugal fan is commonly used, there are some problems in use. As the axial flow fan, the use of the process will produce noise. What causes the noise?
When the blade of axial flow fan is thin and the center of gravity deviates from the center of Blade section, the centrifugal force caused by high speed and the variation of blade lift caused by the instability of intake flow are easy to stimulate the blade vibration. At the same time, because of the fluid fixed coupling, may also lead to blade vibration, so that the blade fatigue damage ahead of time, reduce fan efficiency, resulting in greater aerodynamic noise.
The mode vibration of impeller is mainly composed of four blades with different circumferential vibration. This is mainly because the stiffness of the front blade is much less than the stiffness of the hub, that is, the stiffness of the blade is“Soft” and the stiffness of the hub is“Hard”, but the high frequency is mainly the blade bending wave. In view of the influence of noise, the first six-order vibration has a greater influence on the flow field, because its pendulum has a greater influence on the flow field, which leads to the change of the inlet attack angle of the blade, thus forming the fluctuation of the lift force on the blade surface, in severe cases, vibration will occur, resulting in a large number of aerodynamic noise, reducing efficiency.
To understand the causes of noise produced by axial flow fan, attention should be paid to reduce the production of noise in use.