Tubulent Noise Generted by a Malti-Blades Centrifugal Fans

The fan noise consists of the turbulent noise and the discrete frequency noise. On the multi-blades centrifugal fan, the spectral form is relatively smooth over a wide range of frequency without distinct discrete peak. Therefore the noise observed away from the fan is the turbulent noise. In this report, we proposed a new method to calculate the width of wake which is an important parameter to controll the turbulent noise. The effects of four parameters : the location of partition, the bare ratio, the outlet angle of scroll casing and the chord length of impeller on the turbulent noise were investigated. On the fan noise, it was shown that the fan noise become lower when the bare ratio was around between 9% to 25% and the outlet angle of scroll casing was around 0° to 20°, then the noise of the dual-cascade centrifugal fan were superior to that of the single-cascade centrifugal fan. The location of partition is the best from the point of fan noise when the area ratio of upper cascade was equal to that of the lower cascade and these area ratios are equal to about unity. The agreement between the predicted and measured values of the sound pressure level was satisfactory