Abstract
The object of the present study is to search sound sources on rotating blade surfaces of propeller fan by measuring distribution of pressure fluctuating part. Such experimental studies have seldom been found. The experiments were carried out on two new types of fans applicable to air conditioning system. One of them is an aerofoil type and the other is a thin plate type. The causes of noise are discussed using the experimental results of frequency spectrum of sound and of cross correlation between pressure fluctuating part on rotating fan blade and sound pressure at a point downstream of the fan. The following conclusions are obtained: 1) Noise due to blade vibration is negligibly low because of use of good damping materials. 2) Source of rotation sound is found at the leading edge part and the pressure fluctuating part with broad band higher spectrums is observed at the tip side of the trailing edge part. 3) Noise downstream of a fan is affected by time derivative of the pressure fluctuating part on rotating blade surfaces.
