Noise Reduction in Centrifugal Fans by the Use of Lambda/4 Resonators

摘要

Aerodynamic blade passage noise reduction, using a resonator at the cutoff of a centrifugal fan, is described. While preserving the original cutoff geometry, the perforated mouth of the resonator forms the new cutoff. The resonator can be tuned to various frequencies, e.g., the blade passing frequency, via a movable end plug, enabling tone intensity to be reduced by up to 29 dB. Attenuation of a lesser degree occurs within a frequency band around the resonance frequency. The bandwidth of the resonator response is influenced by the porosity of the resonator mouth. Substantial noise reductions are observed in inlet and outlet ducts over a wide range of aerodynamic loading conditions. The volume flow pumped through a given duct system is changed by less than 1% when the resonator is used.