Higher-order free-wake method for propeller-wing systems

A higher-order free-wake (HOFW) method has been developed to enable conceptual design-space explorations of propeller-wing systems. The method uses higher-order vorticity elements to represent the wings and propeller blades as lifting surfaces. The higher-order elements allow for improved force resolution and more intrinsically computationally stable wakes than a comparable vortex-lattice method, while retaining the relative ease of geometric representation inherent to such methods. The propeller and wing surfaces and wakes are modeled within the same flowfield, thus accounting for mutual interaction without the need for empirical models. Time-averaged results found using the HOFW method are compared with experimental propeller, proprotor, and propeller-wing system data, along with two semi-empirical methods. The results show that the method is well suited for performance prediction of lightly loaded propellers/proprotors and propeller-wing systems and can successfully predict design trends. In addition, the time required to define a geometry and solve for the flowfield with the HOFW method as compared to that required with a computational fluid dynamics method make it particularly useful for design-space exploration. These strengths were highlighted through a sample design study on a generic distributed propulsion vehicle.