Unducted Fan Aerodynamic Design

A method being used to design unducted fans, which are counterrotating propellers with unusually high disk loadings, is described. The quasi-three-dimensional approach employed is similar to that used for ducted fan designs; it consists of a circumferential-average flowfield analysis followed by cascade designs that include secondary flow and sweep effects. The open-tip condition enters as a significant secondary flow contribution. Blade shapes defined by this process are analyzed by a three-dimensional Euler solver and final adjustments are made as necessary. Examples of application of the method are presented to elucidate the magnitudes of the phenomena involved.