The specific noise reduction methods of the fan are as follows:

(1) Enhance the aerodynamic load of the cascade and reduce the circumferential speed

For the axial cooling fan, strong forward blades are used, and the multi blade impeller is beneficial to increase the aerodynamic load of the cascade. Under the same air volume and pressure, the circumferential speed on the outer circle of the impeller blade can significantly reduce the fan noise.

(2) Set up a zigzag structure on the air inlet and outlet sides of the moving blade

The zigzag structure is set on the inlet and outlet side of the moving blade, which can make the laminar boundary layer on the blade convert into turbulence earlier, so as to avoid vortex separation caused by unstable waves in the laminar boundary layer, vortex separation and noise reduction.

(3) Inclination of cochlear tongue

The periodic pulsating aerodynamic force generated by the periodic pulsating velocity of the air flow in the fan impeller cascade also causes the interaction of the volute tongue to produce rotating noise. The magnitude of the noise is related to the intensity of the pulsating aerodynamic force and the windward area of the vortex tongue. If the volute tongue of the centrifugal cooling fan is inclined, the action area of the pulsating aerodynamic force in the same phase will be small, and the radiated noise will be reduced.

(4) Add a turbulizer at the inlet (outlet) of the impeller

Adding a turbulizer (metal mesh) at the inlet or outlet of the impeller blade of the brushless exhaust fan can immediately convert the laminar boundary layer on the back of the blade into a turbulent boundary layer, delay the separation of the boundary layer on the back of the blade, or even not. When the rear edge of the blade is installed on the mesh, the air velocity and pressure gradient behind the mesh can be quickly uniform. If the mesh is in the vortex region, the vortex region can be greatly reduced, and the noise can be further reduced.

(5) Reasonable space and radius of cochlear tongue

When the airflow moves relative to the blade, the velocity and pressure in the wake of the blade trailing edge are lower than those in the mainstream area, which makes the distribution of the velocity and pressure behind the cascade uneven, and the uneven airflow is rotating. Due to the existence of volute tongue at the airflow outlet of the moving blade, the interaction between this unstable flow and volute tongue will produce noise. The closer to the noise, the more intense the noise is, Generally, the rotating noise and eddy current noise of centrifugal fan can be reduced by appropriately taking a larger radius of the front end of the wind tongue.

(6) Set up an acoustic resonator at the volute tongue

An acoustic resonator is arranged at the volute tongue. When the acoustic wave is transmitted to the resonator, the gas in the aperture of the small hole and the cavity moves back and forth under the action of the acoustic wave. The moving gas has a certain mass, which resists the movement caused by the acoustic wave. At the same time, when the acoustic wave enters the aperture of the small hole, a considerable part of the acoustic energy is lost due to heat loss due to the friction and damping of the neck wall. In addition, the cavity filled with gas has the characteristic of blocking the pressure change from the small hole. Because of these factors, the noise is reduced when the gas passes through the resonator.