Multi-Port Eduction of Installation Effects Applied to a Small Axial Fan

In HVAC or domestic appliance applications, industrial fan noise is usually characterized under uniform inflow profile. However, those ideal conditions are rarely met when the fan is installed in its final product. The fan is often in the wake of an obstacle or after a bend, which causes non-uniform ingested flow. Under those distorted inflow condition, the fan noise signature changes causing an increase in noise power level. This paper presents a multiport eduction technique to investigate those installation effects in a compact axial fan situated in a circular duct. The noise emitted by the fan was compared to independent measurements performed using the ISO-5136 method to highlight the benefits of the multi-port technique regarding the elimination of the spectral features caused by the reflections of the acoustic wave on the duct terminations. Installation effects generated by circumferential and turbulence flow distortions were produced using wooden grids. The influence of those grids on the scattering coefficients of the tested module led to an analysis of the changes in acoustic power radiated by the fan under those non-uniform ingested flows.