Characteristics of Blade Passing Frequency Noise of a Centrifugal Fan, and a Method for Noise Reduction

Fan noise data are categorized into source characteristic terms and a frequency response term expressing attenuation in the propagation passage. These terms are determined by sweeping the fan speed from 1000 to 4500 rpm. The fan specific speed and the impeller diameter are 42 and 460 mm. The blade number is 12. By setting the exponent in a power law relationship of sound pressure level versus frequency as 3, two factors describing the source level are determined with simple relationships to the scroll cut-off location. By selecting the distance, the noise level is possibly reduced by more than 10 dB without influencing fan performance. The frequency response if satisfactorily presented by introducing a one-dimensional linear wave model, where the key passage is blade passages selectively determined by the noise wavelength. By choosing the blade number or the inlet duct length so that a frequency of the maximum attenuation is achieved, a noise reduction of 10 dB is again expected.