Fluid dynamics analysis of ducted counter-rotating fans for UAV applications

This paper presents initial results from a study to analyze and optimize the complex flow inside a duct with two counter-rotating fans. The duct is part of a VTOL UAV with conventional control surfaces in the duct exhaust. The aim of the project is to optimize the duct and fan geometry as well as fan placement to achieve high thrust and controllability. The parameters to be investigated are the geometry of duct, the tip clearance between the propeller and the duct, the spacing between the two propellers and the choice of short-chord propellers versus large-chord fans. Catia V5 is used to the design of the vehicle and ANSYS CFX for aerodynamic analysis. The ducted-fan UAV design has been evaluated in wind tunnel tests and has shown promising results. The objective of this study is to further optimize the duct and propeller arrangement and to confirm the results in the wind tunnel.