The aerodynamic and noise characteristics of centrifugal fan with partially tilted tongue

Tilted tongue is one of the very effective solutions to reduce the noise of centrifugal fans. In this study, the accuracy of the numerical simulations is verified by experimentally measured aerodynamic performance and acoustic spectra. Two localized tilting designs of the tongue are proposed with the aim of reducing the aerodynamic noise of the centrifugal fan. Numerical results show that the different approaches significantly affect the noise reduction of the fan, with the best design exhibiting up to 2.33 dB of noise reduction. The internal flow and acoustic fields are analyzed in conjunction with the dynamic modal decomposition method to reveal the effect of the local tilt of the tongue on the flow and acoustic characteristics of the fan. The structural change induces the separation vortices at the trailing edge of the blades and the generation of secondary flow at the outlet wall of the volute shell, which is the main reason for the slight degradation of the aerodynamic characteristics of the fan. The causes of the blade passage frequency (BPF) noise reduction are not identical for different orders. BPF noise reduction stems from diminishing source intensity and dispersing source phase. Noise reduction in 2BPF is mostly due to weakening sound source intensity, with less conspicuous phase dispersion. This study provides good theoretical support for the design of backward curved centrifugal fans in the context of noise reduction.