Influence of the shroud leading edge shape on the axial-fan noise

The paper is focused on the noise reduction of the low-pressure axial fan by the modification of the shroud leading edge shape. The CFD and CAA simulations of the fan are performed on commercial software PowerFLOW based on the Lattice Boltzmann method. The propagation of the acoustics waves to the far-field was carried out by the Ffowcs-Williams & Hawkings acoustics analogy. The far-field acoustic data from the simulation matches with the results from the ISO measurement in the semi-anechoic chamber. Direct acoustics results of the near-field capture dominant noise sources of the cooling axial fan in blade tip area. Vortexes produced by the flow separation from the shroud inlet edge are carried by the rotating fan blade. The interaction of these flow structures with the blade tip surface produces strong subharmonic component in the acoustic spectra with lower frequency compared to blade passing frequency. Four different shrouds geometry modifications are analyzed. The modification of the shape eliminates subharmonic component of the fan sound spectra and reduces overall fan noise.