Dynamic Stall and Vortex Dynamics of a Single Blade in Cycloidal Rotation around an Advance Ratio of One

Cycloidal Rotors have been studied for over 100 years with a focus on applications in energy production (VAWT) and for VTOL vehicles. Numerous experimental and analytical studies have been carried out over the years to prove their potential competency over the conventional horizontal-axis rotors. In contrast, the present study focuses on extending the fundamental understanding of the unsteady aerodynamics associated with cycloidal rotor operation. In particular, particle image velocimetry (PIV) measurements and analytical tools were used to understand the change in flow dynamics around a single, fixed-pitch cycloidally rotating NACA 0012 blade as the system translates across an advance ratio (μ = U_∞/ω R) of 1. Note that μ = 1 represents a critical transition point for the self-start of VAWTs and the progression of VTOL vehicles into forward flight. Preliminary analysis of PIV data shows that the flow is self-similar for cases at the same advance ratio, and that the wake structures do not depend upon the Reynolds number. The phase-history, velocity contour plots of the wake structure show a distinct cycloidal pattern for an advance ratio of 1.25, a more stationary wake pattern for an advance ratio of 1, and a retarding pattern for an advance ratio of 0.75.