The reasons for the noise of large industrial fans may be the following:
1. Vibration.
If the rotor of the fan is rotating, its physical center of mass and the center of inertia of the rotating shaft are not on the same axis, which will cause the rotor to be unbalanced, resulting in vibration and noise.
2. Wind noise.
When the fan is operating, noise is generated due to the fact that the blades are periodically subjected to the pulsating force of the uneven air flow at the outlet. In addition, the uneven pressure distribution of the blade itself and on the blade makes it easy to disturb the surrounding gases and parts during rotation, resulting in rotational noise. The turbulent attachment plane, vortex and vortex detachment generated when the gas flows through the blade can also cause the pulsation of the pressure distribution on the blade, resulting in vortex noise.
3. System impedance.
The range between the air inlet and outlet of the casing accounts for 60%~80% of the total system impedance, and the larger the airflow, the higher the noise. The higher the system impedance, the greater the airflow required for cooling, so in order to reduce noise, the system impedance must be kept within a certain range.
4. Turbulent airflow.
Obstructions encountered along the airflow path can create turbulence and thus noise. Therefore, obstructions should be avoided in the critical air inlet and outlet areas.
5. Fan speed and size.
High-speed fans produce more noise than low-speed fans, so low-speed fans should be used whenever possible. Large, low-speed fans are generally quieter than smaller, high-speed fans.