A Study on Discrete Frequency Noise Generated by Interaction between the Wake of a Centrifugal Impeller and a Cylinder (2nd Report; Prediction of the Interaction Noise)

摘要

In the first report, 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 was discussed. From results of the analysis on the interaction noise and flow around the cylinder, a several experimental characteristics have been obtained. In the second report, in order to predict the interaction noise generated from a centrifugal fan, the prediction theory of the noise level based on the wake characteristics of the centrifugal impeller is proposed. In the prediction theory, the drag in the wake of the centrifugal impeller is applied for the periodic fluctuation phenomenon of the momentum on the solid surface of the cylinder. The noise level of the predicted value was able to estimate quantitatively decrease of the interaction noise by the diffusion of the wake.