Performance, aeroacoustics and feature extraction of an axial flow fan with abnormal blade angle

Abstract

The effect of the deviation angle of an abnormal blade Δβ on the performance of an axial fan is investigated using 3D steady simulation. The sound pressure distribution in the time and frequency domains is examined using LES (large eddy simulation) and FW–H (Ffowcs Williams–Hawkings) noise model. The energy features of the sound pressure are extracted using WPD (wavelet packet decomposition) and EMD (empirical mode decomposition). The results show that under the abnormal condition, fan performance is lower than normal value and the noise rises. The main noise sources are concentrated on the leading edge and tip of the suction surface. The aerodynamic noise is generated mainly by low-frequency sound, and the impeller exhibits an obvious broadband sound feature. In the regions outside of the impeller, the wavelet packet energy in the fundamental frequency band under abnormal conditions is much lower than that under the normal condition, and the difference becomes significant with increasing Δβ. The EMD energy features appear as obvious changes in the relative percentages of the intrinsic mode function energies; the energy entropy is closely related to the deviation angle. The characteristics obtained by WPD and EMD provide significant references for detecting the deviation angle in axial flow fans.