Aerodynamic Analysis of an Unmanned Cyclogiro Aircraft 2018-01-6005
Very little is currently known of the aerodynamic interaction between neighboring cycloidal rotors. Such knowledge is, however, of crucial importance to tune the controller and rotor disposition of a cyclogiro aircraft. Thus, a three-dimensional computational fluid dynamics (CFD) model is developed, validated, and used to analyze the D-Dalus L1 four-rotor unmanned aircraft operating under several configurations. The model solves the Euler equations using the OpenFOAM toolbox in order to provide fast results on a desktop computer. Validation is performed against thrust forces and flow streamlines obtained during wind tunnel experiments at various flight velocities. Numerical results from CFD match the trends of the experimental data. Flow behavior matches the video footage of the wind tunnel tests. Although boundary layer effects are neglected, satisfactory results are obtained both qualitatively and quantitatively. This paper concentrates on the results, while a companion paper covers the model development. It is found that rotor flow, efficiency, and interaction with the airframe are considerably different between hover and forward flight conditions. It is also confirmed that the same flow particle hits the rotor blades more than once and thus generates strong inner vortices. High pitch magnitudes lead to excessive power consumption while not significantly improving the thrust. CFD is able to model the effects of dynamic pitching, the vortices inside the rotor, and the 3D flow toward the endplates. Finally, airframe modifications for less flow blockage, higher rear rotors, and an adapted pitching schedule may bring considerable efficiency increases to the studied cyclogiro.