Force generation of bio-inspired hover kinematics

Abstract

This paper presents the results of an experimental study of the aerodynamics of an elliptical flap plate wing in pitch-plunge motion. Several wing motion kinematics are derived from the kinematics of the Agrius Convolvuli (hawk moth) in hover. The experiments are conducted at a Reynolds number of 4, 800 and reduced frequency of 0.38, which are typical of the hawk moth flight. Three cases are reported: the hawk moth kinematics in which the elevation angle is ignored, the hawk moth kinematics with a correction to account for elevation angle effects, and a harmonic pitch-plunge kinematic of the same frequency and amplitude as the hawk moth kinematics. In all cases the wing pivots about the leading edge. The experiments are performed in The University of Michigan water channel. The wing model used has a Zimmerman planform shape with aspect ratio 3.87. Phase averaged force measurements are reported. Average thrust coefficients of 2.79, 2.64 and 2.39, respectively, are measured for the three cases. The measured peak thrust coefficients are 5.0, 4.8 and 6.1, respectively. The propulsion figure of merit in hover was also measured and found to be 0.47, 0.48 and 0.49 for the three cases. The flow evolution was measured using PIV. The results show formation of Leading Edge Vortices (LEV) and Trailing Edge Vortices (TEV) at different phases of the motion which depend on the particular kinematics. The relation between LEV and TEV vortex evolution and force generation is discussed.