Improvement in Aerodynamic and Aeroacoustic Performances of Axial-Flow Fan in Outdoor Unit of Air-conditioner Using Two-Dimensional Cascade Analysis

As the number of fan blades decreases at the same solidity, the height of the fan increases so that the three-dimensional flow effects become more important due to the stronger swirling flow. Therefore, it is difficult to apply the traditional fan design process based on the performance curves of a single airfoil. In this study, the two-dimensional cascade of airfoils is employed to improve aerodynamic and aeroacoustic performances of the existing axial-flow fan used to cool an outdoor unit of the air-conditioner. The cascades of airfoils at the selected radial locations of the targeted fan blade are extracted. Then, the aerodynamic performances of a two-dimensional cascade of airfoils are analyzed by solving the incompressible RANS equations using the computational fluid dynamic techniques. The variations of lift and drag forces of the cascade of airfoils are examined by changing the pitch angle. The pitch angles for each cascade are determined for the maximum lift and the lowest lift to drag ratio, respectively. The targeted fan is modified by applying the determined pitch angles at the selected radial locations. The aerodynamic and aeroacoustic performances of the modified fans are numerically analyzed, which shows the same trends as those obtained from the cascade analysis. Finally, the prototype of the new fan of which the pitch angles are determined for the maximum lift to drag ratio is manufactured, and its performances are measured. There is an excellent agreement between the numerical and experimental results. These results reveal that cascade analysis can be used as a design tool for fans.