Abstract
Pitching flat plates are a useful simplification of flapping wings, and their study can provide useful insights into unsteady force generation. Non-circulatory and circulatory lift producing mechanisms for low Reynolds number pitching flat plates are investigated. A series of experiments are designed to measure forces and study the unsteady flowfield development. Two pitch axis positions are investigated, namely a leading edge and a mid-chord pitch axis. A novel PIV approach using twin laser lightsheets is shown to be effective at acquiring full field of view velocity data when an opaque wing model is used. Leading-edge vortex (LEV) circulations are extracted from velocity field data, using a Lamb–Oseen vortex fitting algorithm. LEV and trailing-edge vortex positions are also extracted. It is shown that the circulation of the LEV, as determined from PIV data, approximately matches the general trend of an unmodified Wagner function for a leading edge pitch axis and a modified Wagner function for a mid-chord pitch axis. Comparison of experimentally measured lift correlates well with the prediction of a reduced-order model for a LE pitch axis.
Highlights
The recent rise of micro-air vehicles (MAVs) has been profound
The Reynolds number and pitch kinematics were chosen to be representative of the insect/MAV flight regime
Comparing streamlines derived from particle image velocimetry (PIV) data with dye flow streaklines gives additional insight
Summary
The recent rise of micro-air vehicles (MAVs) has been profound. These miniature fliers have a wide range of revolutionary applications including, but not limited to, real-time data delivery surveillance (Davis et al 1996) and exo-planetary exploration (Young et al 2000). MAVs can use flapping wing designs to take advantage of unsteady effects at low Reynolds numbers (Petricca et al 2011). Flapping wing-style MAV designs could be improved with a better understanding of the governing physics of flapping wing motions. More efficient flapping movements could provide longer battery life and increase flight duration. Of particular interest in the generation of an efficient motion is the fluid mechanical process by which lift is generated
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