Installation effects on axial fans: Combined aeroacoustic and psychoacoustic perspective

Low-speed axial fans for engineering cooling applications are often operating in the vicinity of humans. Over the last decades, an effort to mitigate fan noise has been observed. Novel fan designs with substantial noise abatement and little to no expense on aerodynamic performance have been achieved. However, the case of unfavorable installation conditions, namely fans immersed in non-ideal inlet flows, still complicates the optimization of fan designs with regard to acoustic performance. In this study, the acoustic performance alteration of a low-speed axial fan with a rotating ring is documented. Different inlet geometries are tested, while the fan aerodynamic performance is also monitored. The acoustic performance of the fan, including sound power and sound quality metrics, is discussed for three operating points. Furthermore, a parallel fan setup is tested to study the emergence of acoustic interference. Results show marginal gains in aerodynamic performance for elongated inlet geometries. On the contrary, acoustic performance and sound quality are negatively affected, particularly at high loading. Moreover, the inlet configuration with an elongated straight duct demonstrates weak coupling to loading conditions concerning sound power and roughness. An overall consistent scaling of aerodynamic and acoustic performance is observed for the parallel fan system when compared to the single fan case, irrespective of inlet geometry. Sound quality estimates of two incoherent sound sources agree well with measured values of the parallel fan system, apart from fluctuation strength, which is overestimated at stall conditions. • Bell-mouth shaped inlets can lead to increased sound power for rotating ring fans. • Psychoacoustics of axial fans at high loads can be favored with straight duct inlets. • Acoustics of axial parallel fan systems can be described as incoherent fan sources.