Fan noise - Noise prediction and reduction methods

Fan noise arises primarily from unsteady aerodynamic phenomena associated with the interaction of blades and fixed parts with the flow. Depending on the type of fan — described in the article [BM 4 177] —, different mechanisms are responsible for aerodynamic noise, some of which are modeled under certain assumptions. Suitable noise reduction methods are available. Given the complexity of the subject, however, many grey areas remain in the understanding and prediction of fan noise, steps which are necessary for the development of effective noise reduction methods, particularly for broadband noise, which often makes a dominant contribution to overall noise levels. Promising avenues of research are emerging in this field, thanks to advances in the numerical simulation of stationary and, above all, unsteady flows, and in the modelling of aeroacoustic sources, but there is still a long way to go before we can accurately predict the sound power spectrum of a fan as a function of its geometry and operating point.

To reduce the noise of a device or a circuit into which a fan is inserted, it is not enough to reduce the noise of the fan alone, we must also take care to minimize the installation effect, which most often results in an increase in noise level. Methods are now becoming operational to anticipate and reduce this effect.