Simulation of a Cycloidal Rotor System Using an Overset RANS Solver

A compressible Reynolds-Averaged Navier-Stokes solver was used to investigate the performance and flow physics of the cycloidal rotor (cyclocopter), essentially a "horizontal axis rotary wing" where the blades pitch and rotate parallel to the rotational axis. The current work seeks to develop a computational methodology to understand the complex aerodynamics of the cycloidal rotor and its relatively unexplored application for MAVs. The numerical code was validated against RPM and collective pitch angle sweep performancemeasurements; the computed results were found to provide reasonable vertical force prediction, while underpredicting sidewise force and power, possibly due to some unaccounted tare. Velocity field comparisons with PIV exhibited good correlation in capturing essential flow features such as wake skew. The time histories of thrust and power, which are not easily attainable through experiment, reveal a large periodic variations in all the integrated quantities. Such variations make it challenging for CFD to predict the mean sidewise force accurately. Virtual camber effect significantly influences the vertical force time history. Spanwise thrust distribution showed a highly three-dimensional flowfield. Flow visualization, additionally, revealed a very complex flowfield with significant shedding from the blades and a high level of blade-vortex interaction. Overall, the current work seeks to advance the functionality of an existing RANS solver to be applicable to cycloidal rotor geometries, with the purpose of developing a predictive tool to refine the design of future cyclocopter configurations.