Aerodynamic Study of Tilting Asymmetrical Ducted Fans Mounted at the Wing Tips of a VTOL UAV
thesisposted on 24.05.2021, 09:45 by Bahram Raeisi
Tilting ducted fans attached to the wing tips of vertical take-off and landing unmanned aerial vehicles (VTOL UAVs) define new applications for these types of vehicles. This new configuration gives VTOL UAVs the ability to hover like helicopters and fly forward like airplanes. These abilities provide VTOL UAVs with possibility of using any arbitrary location for take-off and landing combined with enhanced range and speed. The thrust vectoring is another advantage of this new configuration, which can be used in most of the necessary maneuvers. The flow behaviour around tilting ducted fans needs to be studied as it has significant effects on the performance of the VTOL UAVs. The first objective of this research is to investigate the use of asymmetrical shape for the external body of ducted fans. This geometry can generate additional lift in cruise mode, which can lead to more applications for the VTOL UAVs by saving more energy. Both CFD and experimental methods showed noticeable improvement in the lift velocity (Vind) of the inlet flow to the rotor plane. This is required for computing aerodynamic coefficients necessary for stability and control analysis of the proposed VTOL UAV. “Actuator Disk Model” combined with the assumption of “Constant Delivered Power” to the propeller were used successfully to calculate Vind for the CFD simulations. The third objective is using CFD coefficient by using an asymmetrical ducted fan. The second objective is to predict the induced simulation for predicting aerodynamic forces and pitching moments of the tilting ducted fans in the transition conditions for different tilting rates. The effects of the stall and flow separation on the aerodynamic coefficients were discussed and compared for both ducted fans. The fourth objective is using the aerodynamic coefficients of the tilting ducted fans to predict and compare the level flight conditions of the proposed VTOL UAV during transition between cruise mode and hover. Results of this research demonstrate satisfactory agreement between CFD simulations and wind tunnel tests for all of these objectives, which could predict the aerodynamic behaviour of the proposed VTOL UAV during transition between cruise mode and hover.