Experimental study and control of noise from a window-type ventilation fan

Noise radiated by ventilation fans is an issue closely related to product competitiveness. The purpose of this experimental study is to identify the noise sources and to seek effective methods of noise reduction. The acoustic directivity and source locations are measured for the original fan and the fans modified for the inlet and exit conditions. Thrust noise dominates the radiated sound. Two main source mechanisms are found to be the unsteady flow caused by non-uniformity of the exit duct and tip leakage flow. Both the inlet and exit modifications are effective in reducing the total noise by about 5 dB and the tonal noise by about 8 dB.