Abstract
The casing of a 235 mm diameter, commercially produced, centrifugal blower was modified by replacing the cut-off of the scroll with a quarter-wavelength resonator. The mouth of the resonator was formed from a perforated plate which had the same curvature as the original cut-off section. Tuning of the resonator was achieved by changing the length via a movable end plug. Noise measurements were made in anechoically terminated inlet and outlet ducts over a range of aerodynamic loading conditions. It was found that the extent of the reductions in the blade passing frequency tones in both the inlet and outlet duct varied with the orientation of and the extent of open area on the mouth perforate. By introducing a splitter in the resonator mouth, substantial reductions in both the inlet and outlet duct were achieved over a large range of aerodynamic loading.
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