Investigation of Aerodynamic Interactions in Ducted Rotor Systems

Computational analysis of a ducted rotor system is performed to investigate aerodynamic interactions of a rotor with a duct in hover. It is hypothesized that the duct contribution to the total system thrust in hover will be higher if the rotor inflow is higher in the blade tip region because of lower pressure on the duct inlet. Thus the optimum inflow requirements for a ducted rotor are different than for an open rotor. Two approaches of varying fidelity are considered. Rotor thrust performance for a rotor containing different radial blade twist distributions is analyzed as both an open and ducted rotor. Actuator disk modeling of the rotor showed that for the same rotor thrust, an outboard dominated inflow distribution generates larger system thrust because of a higher contribution from the duct. Higher fidelity CFD modeling showed that the optimum inflow for the ducted rotor is very different from the optimum for the open rotor. The analysis shows that rotor blade design for a ducted rotor needs to incorporate aerodynamic interactions with the duct to develop an efficient system.