Low-Noise Design of Cross-Flow Fan Based on Frequency Modulation.

The aerodynamic noise generated by the rotating blade row of an electric fan generally consists of a broad-band vortex noise and a narrow-band rotational noise. The rotational noise, called blade passing frequency (BPF) noise, is annoying and its suppression has been considered at the design stage of many types of fans. The authors propose new design methods to reduce BPF level based on sinusoidal frequency modulation and M-sequence frequency modulation. Comparison by means of numerical simulation revealed that M-sequence frequency modulation is superior to sinusoidal frequency modulation with respect to spectral dispersion. Furthermore, it was confirmed that M-sequence frequency modulation realizes successful reduction of the BPF level of the cross-flow fans used in air conditioners.