Characteristics of turbulent noise from backward-curved centrifugal fan with rectangular casing

摘要

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 studied the fan with rectangular casing by experiments and numerical simulation. It is pointed out that the performance of the fan with the rectangular casing is better than that with scroll casing at the large flow rate. The turbulent noise consists of the three frequency ranges, low frequency range under 800Hz, middle frequency range 1200-2700Hz and high frequency range 2700-4000Hz, that have the different noise source. The low frequency range is generated from the impeller, the middle frequency range is mainly generated from the casing wall and the high frequency range is in relating to the flow above the shroud. The secondary flow near the shroud causes the large turbulence and generates the high frequency and large turbulent noise. We proposed the obstacle to reduce the noise level, and then the noise level of high frequency is reduced about 5 dB.