Sound Generation Mechanism in Low Speed Axial Fans

摘要

Because of the global civil regulation concerning acoustic emission,rnmanufacturers aim to substantially decrease the noise radiated by the low speedrnfans, without degrading their aerodynamic performance. To accomplish thisrntarget, engineers must evaluate the unsteady aerodynamic sources in the fanrnrotor responsible for the noise emission. This paper presents the results of thernresearch team’s experimental analysis based on a cause-effect method. Thernprocess focuses on the experimental comparison between the novel prototypes ofrna family of low speed fans and enables the evaluation of the noise sources in thernrotor tip near-field domain. The near-field aerodynamic sources accounted inrnthis work correspond to the zone with high pressure fluctuations amplitudernlocated in the wake region of the rear flow. The team measured the sources at therntip and then correlated them with the fan’s noise emission in the far-field, using arnFourier-based methodology. The paper also investigates the differences inrnhuman perception of noise emission to the environment using a dot-patternrnvisualisation. The study concludes that the modified tip configurations have arnmarked effect on tip-leakage vortex formation by altering the near-wall fluidrnpaths on blade surfaces. The team correlates the modification in rotor noisernemission with the control of tip-leakage flows produced by the tip end-plates.