Reducing Noise from Duct Centrifugal Fans to Improve Airflow

Reducing Noise from Duct Centrifugal Fans to Improve Airflow

A duct centrifugal fan is a machine designed for air circulation. It primarily uses mechanically generated airflow to circulate air within an environment, ensuring a safe working environment for operators. However, as is well known, duct centrifugal fans are mechanical devices that produce significant noise during operation. In work environments such as mines and tunnels, excessive noise can lead to injuries among workers. Therefore, finding ways to reduce noise while maintaining effective air circulation has become crucial. 1. Install silencers on the inlet and outlet ducts of environmentally friendly duct centrifugal fans. In the case of noise from environmentally friendly duct centrifugal fans, airborne noise originates from the air inlet and outlet; thus, it is essential to first reduce local noise. Installing silencers at the inlet and outlet of eco-friendly duct centrifugal fans is an effective measure to suppress fan noise. Currently used silencers are primarily based on resistance and come in many varieties. Resistance-type silencers are commonly used. Typical resistance silencers include tubular, honeycomb, seat, and baffle silencers. 2. Tilt the vanes and increase their clearance and radius. Rotational noise is generated by the interaction of vortex-like vanes with the periodic pulsating aerodynamic forces produced by the layered airflow from the duct centrifugal fan’s impeller. This is related to the intensity of the pulsating aerodynamic forces and the upstream region of the spiral vanes. If the vanes can be tilted, the area affected by in-phase pulsating aerodynamic forces is reduced, and the radiated noise is also reduced. Noise is generated when the rotating airflow—which exhibits non-uniform velocity and pressure distributions behind the cascade—interacts with the vortex tongues. The closer the spacing between them, the greater the noise. Generally, convolutions with a relatively large front radius can reduce the rotational and vortex noise of duct centrifugal fans without affecting the airflow performance of the centrifugal separator. 3. Environmentally friendly duct centrifugal fans utilize rotary diffusers. The space formed by the diameter of the impeller shroud and the impeller disk, which is larger than this diameter, constitutes the rotary diffuser. In conventional open-type or forward-curved propellers, on the other hand, the absolute velocity of the airflow within the blades is very high; once it enters a vortex, it expands rapidly, generating intense vortex noise. Furthermore, the airflow discharge area near the left side of the blade path periodically interacts with the surrounding air, increasing rotational noise. In this scenario, using a rotating diffuser reduces the impeller’s speed, mitigating both of these effects and thereby reducing noise. However, in the case of backward-curved propellers, the noise-reduction effect of the rotating diffuser is not significant. Additionally, if you use a diffuser, you must properly select the radial clearance and angle of the Baine device. Otherwise, significant discrete noise will be generated.