Influence of a micro-perforated duct absorber on sound emission and performance of axial fans

In this article we investigate the influence of varying flow conditions on the acoustic behaviour of a micro-perforated panel absorber (MPA), applied in the vicinity of an axial fan. The predesign of the MPA was conducted by using the Finite Element Method (FE) in combination with porous material modelling approaches. Experimental results of emitted sound spectra and fan characteristic of different fan blade geometries, positioning of the fan to the absorber, as well as changes in turbulent intensity are presented. The studies showed that the investigated MPA duct reduces the overall sound pressure level emitted by the fan by up to 16 dB while maintaining the same efficiency and pressure build-up. From an acoustic and aerodynamic point of view, it was more efficient if the fan operate downstream of the MPA instead of within the MPA. This arrangement increased the efficiency and avoided high-frequency sound generation, which is caused by the flow through the MPA. The results show that the function of the MPA can be used for different fan geometries and that inlet turbulence improves the properties of the absorber.