An Experimental Investigation of a Micro Air Vehicle-Scale Cycloidal Rotor in Forward Flight
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The current research aims to explore the forward flight capability of an unconventional rotary-wing concept for micro air vehicle (MAV) applications, known as the cycloidal rotor (or cyclorotor). Two approaches are undertaken to fulfill this objective: 1) performance studies to examine the time-averaged forces produced by the cyclorotor, and 2) flow field studies to investigate the underlying physics of force production. In the performance studies, the dependence of time-averaged lift, propulsive force and power on blade pitching kinematics, rotor geometry and forward flight operating conditions (i.e. advance ratio) were first examined through independent parametric studies. Next, the performance results were interpolated to determine the steady level flight characteristics of the cyclorotor, specifically the power consumption, lift-to-drag ratio and control input requirements at various forward speeds. The baseline values of lift and rotational speed for these trimmed flight studies were determined based on an existing twin-cyclorotor MAV. These studies showed the cyclorotor to be capable of achieving relatively high advance ratios (up to 0.94), with significant reductions in power consumption. In the second research approach, flow visualization experiments and time-resolved, planar particle image velocimetry (PIV) measurements were performed to gain a qualitative and quantitative understanding of the flow field. The time-averaged and phase-averaged flow fields of a 2-bladed cyclorotor were examined at different advance ratios. The PIV measurements were then correlated with previous computational fluid dynamics (CFD) simulations to help explain the distribution of forces along the rotor azimuth. The flow field studies revealed that the cyclorotor needs to operate in the counter-clockwise direction (freestream velocity from left to right) in order to produce the necessary lift force in high-speed forward flight, the primary lift and propulsive force producing regions of the cyclorotor are located in the lower-rear half of the rotor azimuth (symmetric pitching kinematics), and that unsteady aerodynamics (e.g. blade-vortex interactions) plays an important role in the generation of lift and propulsive blade force production.