Aerodynamic Performance and Interaction Effects of Circular and Square Ducted Propellers

Abstract

Ducted propellers constitute an efficient propulsion-system alternative to reduce the environmental impact of aircraft. These systems are able to increase the thrust-to-power ratio of a propeller system by both producing thrust and by lowering tip losses of propellers. In this research, steady and unsteady RANS CFD simulations were used to analyze the possible impact of modifying a propeller duct shape from a circular to a square geometry. Initially, the two duct designs and the propeller were studied separately, in order to estimate the numerical errors and to compare with existing data. In the installed simulations, the propeller was first modelled as an actuator disk, and afterwards with a full blade model, in order to understand the time-averaged influence of the propeller on the duct before studying the complete unsteady propeller-duct interaction. In the current design, the square duct corners were found to be prone to separation, and to contribute towards the generation of strong vortices. Furthermore, due to the reduced leading-edge suction on the square duct, the square ducted system was found to be 4.5% less efficient than the circular one, for the conditions tested. By relating the aerodynamic interaction phenomena to the performance of the system, this study provides and important basis for the design of unconventional ducted systems.