Experimental Investigation on the Noise Characteristics of a Squirrel-Cage Fan with Different Blade Lengths

Squirrel-cage fans are widely applied in air conditioning systems, and their aerodynamic noise mainly related to blade length. The aerodynamic performance and noise spectrum of squirrel-cage fans are synchronously measured in an anechoic wind tunnel. The effect of blade lengths and different geometric configurations on the noise of a squirrel-cage fan is experimentally investigated. This paper focuses on the total sound pressure level and noise spectrum characteristics at different measurement points. Noise distributions of the outlet of the forward squirrel-cage fan exhibited axial-symmetry and large differences for those of vertical direction. In lower fan positions, the noise was greater than that of the top. In particular, it was found that blades were easy to generate higher noise when their length was reduced by 31.7%. The findings suggest that the broadband noise of the squirrel-cage fan should be fully considered for noise reduction. The purpose of this work is to provide a novelty reference for the low-cost modification method of cutting blades. The results show that fans with shorter blades have lower noise and kept an excellent performance. These finding have implications for fan manufacturers.