Effect of Flexibility on Flapping Propulsion
INDIAN INST OF SCIENCE BANGALORE (INDIA)
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The main objective of the work was to understand the effect of flexibility on flapping foils. Flexibility is inevitably present, though, to different degrees, in the wings of many natural fliers and in the fins and tails of fish. The loads on such foils are related to the circulations developed around the foils and indirectly to the circulations in the vortices that are shed in the wake. The foils and fins in nature are three dimensional and the interactions between the fluid and the flexible surfaces complex. The present study was aimed at having a simple experimental model to study the effect of flexibility on the flow. Towards this end we studied the flow field due to a pitching 2-dimensional NACA 0015 foil, to which was attached flexible flap. Two types of experiments were conducted with the flapping foil to which was attached a flexible foil. One was with forward motion or with a free-stream velocity. The other was in stationary fluid. In the first set, flow fields were investigated using dye visualization and PIV for flapping foils with and without the flap. The flexible flap substantially changed the flow field. In the second set, i.e., flow generated without free stream, in stationary water, a new type of hovering mechanism was discovered.
- Pilotless Aircraft