On the Performance and Flight Mechanics Analysis of Ducted Rotors - Axial Flight

Abstract

A literature survey on ducted rotors revealed that some operating conditions are not captured yet by modeling efforts using the blade element momentum theory. The principal flow conditions missing a solution are presented and possible application cases are outlined. A unification of the inflow calculation for open and ducted rotors in hover and climb condition is proposed and implemented into the Versatile Aeromechanics Simulation Tool. Wind tunnel data are used to validate the complete model including an airloads calculation based on tabulated airfoil data. Satisfactory performance predictions were obtained in the open as well as the ducted rotor validation except for high thrust levels. Large deviations from test data were observed in the wind speed results using the geometrical contraction factor of the shroud in the simulations, whereas assuming a cylindrical duct yielded a good match. Further investigations are needed to identify whether the formulation basing the flow contraction on geometry is unsuited in general or improves results for other ducted rotor configurations. The application of tip losses onto the inflow instead of as a factor on the airloads leads to a physically more meaningful simulation of the flow field. It also improved the agreement with experimental data for high thrust cases in this study.