Multi-Objective Design of a Distributed Ducted Fan System

The distributed propulsion system applied to the vertical take-off and landing aircraft must maintain the high performance in both hover and cruise flight. The gap of the power unit has an adverse effect on the distributed ducted fan system, especially in cruise flight. Therefore, a new distributed ducted fan system was proposed, which eliminated the power gap in design, and adjusted the contraction and expansion of the wake through the deflectable induced wing arranged behind the ducted fan to ensure the high efficiency of the distributed ducted fan system in different flight phases. Then, a multi-objective design method of the distributed ducted fan system was proposed, and the feasibility of the design method was verified by designing the inlet and outlet of the duct and the induced wing. Design results show that the performance change of the distributed ducted fan system mainly came from the change of the inlet. By increasing the length and height of the inlet, the flow separation was alleviated and the duct thrust was increased in hove flight, but the cruise drag became larger. The increase of the inlet height made the operating point of the blade far away in hover and cruise flight, which increased the difficulty of the multi-objective design. Compared with the distributed ducted fan system composed of the traditional circular ducted fan, the hovering power load was reduced by 3.703%, but the cruise efficiency was increased by 17.372%, and the spanwise space was reduced by 20% in the final design.