Installed acoustic performance of cooling axial fans fitted with end-plates

In this study, the airborne noise generated by an axial fan installed in a draftcooled unit is studied. The fan is tested without, and with three different blade-tip end-plates. The standard en-plate geometric has a constant thickness (TF) while the others two end-plates (TFvte and TFmvb) are designed to deliberately control the swirl level of the blade tip leakage vortex. Results have proven that these end-plates reduce the tip-leakage flow and vortex formation, which in turn has a favourable impact on the axial fan noise signature in standardised airways. This study uses both free-field standardised airways, and to reproduce installation effects an induced draft configuration over a set of tube banks to distort the axial fan inflow. The paper discusses far-field noise measurements in terms of spectral analysis and directivity for the different end-plate configurations. Although installation effects alter the noise signature of the tested rotors, the TFmvb end-plate design outperforms the other rotors, as a consequence of the high control of the tip flow, resulting also in lower harmonic tones.