Performance and Flowfield Measurements of a Meso-Scale Cycloidal Rotor in Hover

Abstract

This paper details the performance and flowfield measurements on a meso-scale cycloidal rotor. Owing to the small size (rotor radius of 1 inch), the cycloidal rotor investigated in the present study operates at ultralow Reynolds numbers (Re∼11,000) and also utilizes a blade design completely different from the previous studies. The meso-scale rotor utilizes a low aspect ratio cantilevered blade design with flat plate airfoil and elliptical blade planform, which means that 3-dimensional effects will be more prominent. A highly sensitive, miniature 3-component balance was developed to measure the vertical and sideward thrust, torque, and rpm with varying number of blades, pitch amplitude, and blade aspect ratio (with constant blade area). The studies showed the highest efficiency was achieved with higher number of blades (4 – 6 blades), high pitch amplitude (40° – 45°) and moderate aspect ratios. Phase-locked flowfield measurements were conducted using Particle Image Velocimetry (PIV) technique in two different orientations, chordwise and spanwise measurements. The chordwise measurements had the laser plane normal to the rotational-axis/blade-span and examined the evolution of leading edge vortices and the trailing wake at 60% blade span location. The spanwise measurements had the laser plane parallel to the axis of rotation, bisecting the rotor vertically to examine the evolution of blade tip and root vortices. PIV measurements show that the flowfield on the present meso-scale cycloidal rotor is highly 3-dimensional and unsteady, characterized by the growth and shedding of leading edge vortices (LEVs) and trailing vortex sheet similar to the ones 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.