The blade periodically strikes the air mass when the fan is operating under certain pressure conditions
In recent years, research has found that because the infrasound decays very little during the propagation process, even if it is far away from the sound source, we will suffer from it. There are many cavities and elastic systems in the human body, when the external vibration frequency is inherent to a certain part of the human body. When the frequency is the same, it will cause resonance and damage the human body. The aerodynamic noise source of the fan system is complicated due to the noise generated by the fan system. It involves many disciplines. Many experts and scholars at home and abroad have carried out a lot of theoretical research and practical discussion. This paper only discusses some of the reasons based on its own professional characteristics. .
The aerodynamic noise source of the fan generates strong noise when the fan is running under certain working conditions, mainly including rotating noise, eddy current noise, mechanical noise and the like. (1) Rotating noise When the fan is operated under a certain pressure condition, the blade periodically strikes the air mass point, causing the pressure pulsation of the air to form a periodic rotating noise. The fundamental frequency of the rotating noise is the number of times the blade hits the air mass per second. It is related to the number of revolutions of the fan impeller, the number of blades, the flow of the fan, the exhaust pressure, etc. The noise spectrum is characterized by medium and low frequency. (2) Eddy current noise When the fan is operated under a certain pressure condition, a large amount of gas vortex will be formed on the surface of the impeller. When these gas vortices are separated at the impeller interface, a vortex bath sound is generated. The frequency of eddy current noise depends on the shape of the fan blades and the relative speed of the blades and gases. The peripheral velocity of the blade varies with the distance from the center of the circle, and continuously changes from the center of the circle to the maximum peripheral velocity. Therefore, the eddy current noise is a continuous spectrum with medium and high frequency characteristics.
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