Reduction of Turbulent Noise from Backward Curved Centrifugal Fan with Square Casing

C1 - Noise of Centrifugal Fans

The backward-curved centrifugal fan with square casing is used to the air conditioners and the air cleaners that is required the compact and flexible design. We have pointed out that the performance of the fan is better than the fan with scroll casing at the large flow rate. But the noise characteristics of this type fan are not cleared yet. It is investigated the noise characteristics in relating to the interaction between the impeller and the square casing by experiments and numerical simulation.
It is pointed out that the turbulent noise is consists from the three frequency ranges that have the different noise sources. The low frequency range noise is generated from the impeller, the middle frequency range noise is generated from the casing wall and the high frequency range noise is in relating to the shroud flow. The side walls are the main sources of the middle frequency range noise and the one of the side walls is the most important to the middle and high frequency noise. The secondary flow near the shroud causes the large turbulence and generates the high frequency and large turbulent noise. We proposed the obstacle setting to reduce the noise level.