Propeller fans are required not only to have high performance but also to be extremely quiet. The internal flow field of this fan is even more complicated because they usually have the very peculiar configuration with protruding blades upstream. Hence, many kinds of internal vortices yield which causes the noise and their cause and countermeasures are needed to be clarified for the low noise design of propeller fan. In this research, the flow field of the specific blade is clarified by visualization and noise measuring using the phase-lock method. Additionally, based on these results, noise reduction design methodologies are suggested.
