Experimental study on noise reduction of a compact axial fan with leaned vanes

• By positive blade lean design, a significant noise reduction is obtained in a 1.5-stage axial fan experimentally. • The blade lean design exhibits different noise reduction patterns for different noise components. • The directivity behavior of each blade lean design differs for different BPF orders. In this paper, the blade lean design was applied to a 1.5-stage compact axial fan, and its acoustic benefits were fully investigated through a reliable experimental study under five different rotation speeds with the tip Mach number ranging from 0.15 to 0.195. Compared with the original design, three additional sets of positively leaned vanes were employed for these test series. The far-field directivity and spectra analyses were conducted with the objective of investigating different acoustic behaviors in the upstream and downstream fields. Detailed experimental results show that each blade lean design, with negligibly affecting the aerodynamic performance, has achieved both the tonal and broadband noise reduction at all far-field observation angles over the range of rotation speeds. Evaluating different noise components, the relationship between the blade lean angle and noise reduction has been identified. It is found that the broadband noise reduction exhibits a positive correlation with blade lean angle, while the tonal noise reduction appears to have an optimal blade lean design. In summary, an overall sound power level reduction up to 5 dB in the upstream field and 3 dB in the downstream field has been achieved through these leaned vanes.