Noise Reduction Methods for Vortex Noise and Discrete Noise in High-Temperature Centrifugal Fans

Noise Reduction Methods for Vortex Noise and Discrete Noise in High-Temperature Centrifugal Fans

Vortex Noise in High-Temperature Centrifugal Fans. Vortex noise in high-temperature centrifugal fans is generated by various vortices that separate from the airflow. Generally, there are the following four causes. 1. Turbulent noise introduced when an airflow containing a certain degree of turbulence strikes the blades. 2. Boundary layer turbulence noise caused by pulsating turbulent boundary layers as air flows over the blade surface: 3. Out-of-body vortex noise caused by the separation of the turbulent boundary layer at the trailing edge of the high-temperature centrifugal fan: 4. Since the pressure on the concave side is greater than that on the convex side, the secondary flow from the concave to the convex side of the high-temperature centrifugal fan blade is swept away by the main airflow, generating upper vortex noise. Discrete noise in high-temperature centrifugal fans. Discrete noise refers to noise generated by the interaction between the asymmetric structures surrounding the blades and the circumferentially non-uniform flow field formed by the rotational testing of the blade openings. It is generally characterized as follows. 1. Interference noise at the inlet port is caused by the intake duct or metal mesh covering located in front of the inlet port. 2. Rotational frequency noise generated by rough or asymmetric casing panels. 3. Outlet interference noise at the outlet of the high-temperature centrifugal fan is caused by the presence of a convoluted nozzle or the actual guide vanes of the fan. Discrete noise exhibits discrete spectral characteristics; the fundamental frequency (the corresponding frequency when i = 1) exhibits strong noise, so harmonics are correspondingly reduced.