Performance of a ducted propeller designed for UAV applications at zero angle of attack flight: An experimental study

Performance characteristics and velocity field of a 16 inch diameter ducted propeller are investigated experimentally using five different duct shapes. Experiments are conducted at zero angle of attack which simulates takeoff and forward flight modes of a vertical takeoff and landing (VTOL) tilt ducted propeller UAV. Effect of duct geometry is studied by means of force, torque, velocity field and surface pressure measurements under various flow conditions. Force and torque transducers are embedded into motor hub so that they do not disturb the flow. Thrust components acting on duct and propeller are measured individually. Velocity profiles at the inlet and exit sections are measured with hot-wire anemometer. Experimental results obtained for open and ducted propellers are compared. It is shown that power coefficients obtained for all ducted propeller arrangements are lower than that of open propeller which indicates that propeller operates more efficiently inside a duct. However, thrust obtained from the duct decreases and reaches negative values with increasing advance ratio which makes duct unfavorable at high freestream velocities. Pressure measurements show that, the origin of the duct thrust is suction effect induced by the propeller in converging part (forebody) of the duct, and magnitudes of pressure coefficients inside forebody diminish with increasing advance ratio. Optimization of inlet shape for all advance ratio range of the vehicle is essential for a better design.