Development of low-noise centrifugal fans in a refrigerator

In this paper, low-noise centrifugal fans are developed by applying new design concepts which can reduce the airfoilself noise by inducing phase difference of potential sources on trailing edge lines of fan blades in the span-wise direction. These design concepts are realized by modifying existing linear trailing edge lines of fan blades into the inclined S-shaped ones. First, to analyze the detailed mechanisms of noise reduction of newly developed inclined S-shaped fans, numerical analysis is made by using hybrid computational aeroacoustic techniques where the computational fluid dynamics (CFD), the acoustic analogy, and the boundary element method (BEM) are sequentially used. The noise reduction of the new fans is confirmed by comparing the predicted BPF noise components of the new fans with those of the existing fan. In addition, it is found that the turbulent kinetic energy of the fluid, predicted for the inclined S-shaped fans, is less than that for the existing fan. This implies that the main mechanism for the noise reduction of newly developed fans is due to the decreased turbulent kinetic energy, which can be considered as a qualitative index for the source magnitude of broadband self-noise. Finaly, the validity of low-design concepts is confirmed by the experiments carried out with four proto type fans. These results show that noise reductions of approximately 2 to 3.5 dB are achieved for the new fans in comparison with the original fan. These reductions are retained over the range of rotation speed of fans from 1800 rpm to 2400 rpm.