抄録
Speed-dependent characteristics of centrifugal fan noise are discussed by introducing a model of wave transmission through the impeller and the inlet duct. The fan noise data at the inlet are categorized as source strength terms and a frequency-response term expressing attenuation in the propagation passage. By setting the exponent in a power-law relationship of the 2 nd power of sound pressure level versus frequency at 6, i.e., a dipole source, two factors describing the source level are determined with simple relationships to the cut off clearance. The frequency response is satisfactorily predicted by introducing a one-dimensional linear wave model in which the key passage is the blade-to-blade passage selectively determined by the noise wavelength. Through selection of the blade number or the inlet duct length so that the frequency of the maximum attenuation is achieved, the fan noise level is reduced by more than 10 dB, without any influence on fan performance.
