A Study on Discrete Frequency Noise Generated by Interaction between the Wake of a Centrifugal Impeller and a Cylinder (1st Report; Generating Mechanism of Discrete Frequency Noise)

摘要

In order to clarify the influence of the cutoff of the scroll casing on the discrete frequency noise,the dependence of the diameter of a cylinder on the discrete frequency noise generated from interaction with the wake of a centrifugal impeller is discussed. The discrete frequency noise level decreases when the diameter of the cylinder becomes large. The noise is generated by the pressure gradient at the stagnation point on the cylinder surface formed by the jet-wake flow of the impeller. The domain where the stagnation point vibrates extends when the diameter of the cylinder becomes large; the pressure fluctuation has become small according to the diameter. It is shown that the interaction noise generated from the centrifugal fan can be reduced depending on the design of the cutoff shape.