Abstract-
Experiments were done to investigate the role of vortex formation in the
drag force-generation of low aspect ratio, normal flat plates starting from
rest. This very simplified case is a first, fundamental step toward
understanding the more complicated flow of hovering flight, which relies
primarily on drag for propulsion. The relative importance of the plate's
free end, or tip, with varying aspect ratio (AR) was also studied.
Identifying the relationship among AR, vortex formation, and drag force can provide insight into the wing AR's and kinematics found nature, with the eventual goal of designing man-made flapping wing micro air vehicles (MAVs).
The experiments were carried out using flat plate models in a towing tank at a moderate Reynolds number of 3000. Two AR's, 6 and 2, were considered, the latter in order to have a highly tip-dominated case. A force balance measured the time-varying drag, and multiple, perpendicular sections of the flow velocity were measured quantitatively using digital particle image velocimetry (DPIV). Vorticity fields were calculated from the DPIV data, and features in the drag force for different AR's were related to the vortex dynamics. Finally, since the flow is highly 3D, dye flow visualization was done to characterize its structure and to augment the 2D DPIV data.
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