Noise reduction in centrifugal fans: A literature survey

In order to help the industrial engineer construct quieter fans, the research work done by various experimenters during the last fifteen years on noise reduction methods in centrifugal fans used in air conditioning and ventilating equipment is summarized. Only those investigations are included in which an attempt was made to reduce the generated sound by modifying the fan itself. Most of the work described was aimed at reducing the blade passage sound, but in some cases a decrease of the broad band noise was also obtained. Three different centrifugal impeller designs are dealt with: multivane impellers with forward curved blades, impellers with backward curved blades, and impellers with radial blades. The following methods are described: increasing the distance between impeller tip and cutoff, angle of inclination between impeller blades and cutoff edge, staggering of blades of double inlet blowers and double row impellers, and transition meshes at the leading and trailing edges of the rotor blades. Future research work on the main source regions of broadband noise is suggested.