Low-Noise Design for Cross-Flow Fans. Reduction of Blade Passing Tones by Noise Source Interference.

Cross-flow fans often generate rotational noise called blade passing tones. An effective way to reduce noise is to design the shape of the blades so that the interference between the pressure fields of the noise sources eliminate the blade passing tones. The use of the fans whose blades are not straight in the axial direction is therefore increasing. However, the noise reduction effects of fans with such shapes have not been evaluated sufficiently as yet because a proper estimation method has not yet been developed. In this paper, a method for modeling the fan noise is proposed. In this method, the noise sources are approximated as point sources along a line, and an equation for the total acoustic power of the sources is derived. The power reduction effects are calculated for various fan shapes using the proposed model, and the results are discussed.