NOISE REDUCTION METHODS IN CENTRIFUGAL FANS.

A new noise control procedure for centrifugal fans is described which reduces both the harmonic and the random noise component. In conventional design the volute of the fan casing is made from sheet metal and, therefore, is acoustically hard. In the experimental fan described here, the volute of the casing is made from perforated sheet metal covered with a layer of non-woven fabric. The volute itself is mounted in a closed box, and the space between volute and the walls of the box is filled with rockwool. Thus the pressures at the volute which are excited by the turbulent flow in the casing are absorbed before they are radiated into the far-field.