Numerical and experimental investigation into effects of winglet shape on flow and noise performances of axial-flow fans for outdoor unit of air conditioner

In this study, the effects of winglet shape on the flow performance, efficiency, and aerodynamic noise of axial-flow fans, used as cooling fans in an outdoor unit of split-type air-conditioners, are numerically and experimentally investigated. Especially, a focus is placed on the coherent flow structures of the tip and leakage vortices: the former is generated from the fan blade tip near the leading edge, and the latter forms in the gap between the blade tip and the shroud. Two types of axial-flow fans are considered: one is with a blade-tip winglet, and the other is without the blade-tip winglet. The flow fields around the fans are simulated by numerically solving the three-dimensional unsteady incompressible RANS equations, and the radiated acoustic pressure is predicted using the Ffowcs-Williams and Hawkings equation. The validity of the numerical methods is confirmed through the predicted results with the measured ones. The flow field characteristics driven by the fans with and without the winglet are analyzed by comparing the detailed structure of the tip and leakage vortices in the gap flow region. In addition, the flow performance, efficiency, and sound pressure of the axial fans are characterized in association with the vortex structures. These results reveal that the winglet shape in the gap flow region has an adverse effect on the flow and acoustic performances of axial-flow fans by increasing the gap-vortex strength.