Force and Flowfield Measurements on a Rigid Wing Undergoing Hover-Capable Flapping and Pitching Kinematics in Air at MAV-Scale Reynolds Numbers
The paper focuses on understanding the mechanism of force production on a hover capable flapping wing system by utilizing a combination of direct force measurements and flowfield studies. The experi- ments were conducted in air at a Reynolds number of approximately 25,000, which is the typical operating regime of small flapping wing micro air vehicles (MAVs). The forces and moments were measured using a miniature six-component force transducer installed at the wing root. The wing was flapped in air and vacuum at the same frequency and wing kinematics, and the vacuum forces were subtracted from total forces in order to obtain the pure aerodynamic forces. Flow visualization and particle image velocimetry (PIV) were used to characterize the formation, strength, and structure of the leading edge vortex (LEV) on the flapping wing. The process of LEV formation and shedding was observed to be analogous to the classical process of dynamic stall. A rapid increase in wing lift coefficient (Cl) was associated with the growth of the LEV and a progressive reduction in Cl with the convection of the LEV over the chord. The LEV was observed to be stable for the spanwise locations closer to the root (i.e., the 25% span location) and bursted for locations away from the root (50% and 75% span locations) just after the midstroke. High instantaneous lift coefficient values (Clmax=1.85) were measured during the translational phase clearly showing the role of LEV in augmenting lift. However, lift to drag ratios were always less than 1. Aerodynamic efficiency during the translational phase was quantified in terms of figure of merit (FM), which improved with decreasing translational wing pitch angle. The maximum FM value measured was 0.36 at 40 translational pitch angle. 2012 AIAA.
name of conference
54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference