Prediction of spectral distribution of broadband noise generated from an axial flow fan

The authors have experimentally studied on the relation between the periodic velocity fluctuation in the near wake of a rotating blade and the generated broad band noise. Typical periodic velocity fluctuation was clearly caused by Karman vortex shedding and produced a discrete frequency noise. The frequency of the velocity fluctuation increased toward the blade tip. Then the spectrum of noise generated from the whole span of the blade becomes broadband. In addition we have proposed a theory to predict the spectrum of the broadband noise.