Abstract
In order to clarify the major factor of a narrowband noise in the off-design point of a propeller fan, the relative flow field in the blade tip is measured by a hot-wire probe with the phase-lock method. When the propeller fan is operated at the off-design point, the narrowband noise is generated in the lower frequency domain than that of the blade passing frequency. The velocity fluctuation in the leading edge of the blade tip became large at the same frequency band of the narrowband noise.
