The rotational noise of a Centrifugal Ventilation Fans is also referred to as discrete frequency noise or by frequency noise. At the time of operation, when the fan rotates, the exit of the blade passage on the rotating impeller will, to some extent, be along its circumference. Both the airflow pressure and the airflow velocity have large variations. When the clearance between the volute tongue and the blade exit edge is small, periodic pressure and velocity pulsations occur when the rotating blade passage passes over the volute tongue. The noise generated by the pulsation is called rotational noise.
The vortex noise of the Centrifugal Ventilation Fans is also effectively called eddy current noise. In the process of operation, the impeller blade interacts with the gas during the rotation process, and the broadband noise radiated by the coupling is effective when used. It includes turbulent boundary layer noise, trailing edge eddy current shedding noise, tip eddy current noise, and incoming turbulent noise.
When the Centrifugal Ventilation Fans obtains the same wind turtle and wind pressure, the aerodynamic load of the cascade of the Centrifugal Ventilation Fans can be effectively increased, and the peripheral speed of the fan blade can be reduced, thereby achieving the purpose of reducing noise.
The Centrifugal Ventilation Fans can appropriately select the radius of the front end of the volute tongue to a certain extent, which can effectively reduce the rotational noise of the Centrifugal Ventilation Fans. When the volute radius ratio is increased from r/R = 0.01 to 0.2, the maximum noise reduction value is 6 dB. The vortex tip front radius has a much smaller effect on the blade passage frequency than the volute tongue clearance.