Numerical simulations were performed to investigate the sound generation mechanism of a propeller fan in the outdoor unit of an air conditioner. The vortex and separation flow around two- and three-bladed propeller fans were analyzed to locate the sources of noise. A two-bladed fan usually has a lower flow rate than a three-bladed fan at the same rotating speed. In general, a two-bladed fan should increase the rotating speed to obtain the same amount of flow rate as a three-bladed fan. The increased rotating speed of a two-bladed fan may results in a louder noise comparing a three-bladed fan. To overcome this drawback, an optimized two-bladed fan was proposed by increasing the solidity and pitch angle. During optimizing the two-bladed fan, the relative priorities of the design parameters were evaluated to identify the most important, and these parameters were then optimized using the response surface methodology. The overall sound pressure level (OASPL) of the new optimized two-bladed propeller fan was 5.2 dB lower than that of previous two-bladed fans and 1.2 dB lower than that of the optimized three-bladed fan.
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