Abstract
The backward-curved centrifugal fan with rectangular 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 rectangular casing by experiments and numerical simulation. The acoustic transparent wall is used to find out the noise source in the experiments. 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 generated from the shroud. One of the side walls is the most important to the 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.
