Analysis on hub vortex and the improvement of hub shape for noise reduction in an axial flow fan

This study aimed to reduce the flow induced noise in an axial flow fan installed in the outdoor unit of an air conditioner. This study found the reduced fan efficiency due to a vortex produced by the flow separated from the edge of the hub entrance via affecting the fan blade. The vortex increased the turbulent intensity in the fan's wake, which is a major noise source of the fan. This study proposes a new shape for a hub to reduce the hub vortex. The size of the new hub is extremely small, which is 13.6% of the size of the existing hub. The axial fan with the new hub was named "Hubless fan" in this study. Computational fluid dynamics (CFD) analysis on the flow field revealed that the vortex was significantly reduced in the Hubless fan and this resulted in reduction of the turbulent intensity and vorticity in the wake. By measuring the noise of the Hubless fan with microphones in an anechoic room for experimental verification, reduction of the broadband noise at the certain frequencies on the noise spectrum and reduction of the overall sound pressure level by 1.2 dB compared to existing fans were confirmed.