Aerodynamic Performance of a Hovering Cycloidal Rotor: A CFD Study with Experimental Validation

A three-dimensional (3D) unsteady Reynolds averaged Navier-Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed-wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose-up pitch angle in upstream of the rotor axis was 34.8 degrees. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose-up pitch angle of the downstream blade was 38.6 degrees. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.