A Study on Suppressing Acoustic Resonance of Interaction Tones from a Centrifugal Motor Blower (Modeling of the Phenomenon and a Proposal for a Method of Suppression)(Acoustic Noise)

In a centrifugal blower with diffuser vanes, the noise level may increase at certain rates of revolution. In particular, the phenomenon of acoustic resonance due to tones arising from aerodynamic interaction between the impeller and the diffuser is serious. In this paper, we develop a physical model to describe this phenomenon. The model assumes that the flow paths in both the impeller and the diffuser behave as quasi-one-dimensional acoustic tubes. The model predicts the critical rates of revolution at which resonance occurs, and the prediction of the model is verified by experiments. We also propose an effective method for suppressing the resonance. This involves the use of diffuser vanes with slits. Each slit is located just behind the end of the overlapping region between neighboring vanes. The physical model determines this location. Experiments showed that the method successfully reduces sharp peaks in the noise spectrum.