Experimental Studies on a Mesoscale Cycloidal Rotor in Hover
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Copyright 2018 by Thomas A. Reist, David W. Zingg, Mark Rakowitz, Graham Potter, and Sid Banerjee. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. This paper details the performance and flowfield measurements on a mesoscale cycloidal rotor (rotor radius of 1 in.), which operates at ultralow Reynolds numbers (Re 11;000) and uses a design different from previous cycloidal rotor studies. The mesoscale rotor uses a cantilevered blade with a flat-plate airfoil and low-aspect-ratio elliptical blade planform. A three-component balance was developed to measure the vertical and sideward thrust, torque, and rotation frequency as the number of blades, pitch amplitude, and blade aspect ratio were varied. The studies showed that the highest efficiency was achieved with higher number of blades (4-6), high pitch amplitude (40-45 deg), and moderate aspect ratios. Phase-locked flowfield measurements were conducted using a particle image velocimetry (PIV) technique in two different orientations: chordwise and spanwise. PIV measurements show that the flowfield on the present mesoscale cycloidal rotor is highly three-dimensional and unsteady, characterized by the growth and shedding of leading-edge vortices and a trailing-edge vortex sheet similar to that seen on flapping wings; strong root and tip vortices that interact with each other to create an undulating wake; skewed inflow; and the strong interaction of the slip stream from the upper blade on the lower blade.
