Abstract
Past qualitative dye flow visualizations behind a finite-span flapping foil have led to a model of the vortex skeleton. Subsequent 2D PIV experiments have highlighted some salient features in the proposed model but the 2D measurements reveals limited information about a highly 3D flow. This study proposes to use 3C 3D SPIV to quantitatively describe the flow geometry and test the proposed model of the vortex skeleton. This information is used to investigate the mechanisms responsible for thrust production. Preliminary results from 2D 3C SPIV behind a 3D NACA0012 flapping foil with an aspect ratio of 3, at a Strouhal number of 0.35 at the plane of symmetry reveal qualitative information about the reverse Karman vortex street. The structure as seen in the single measured plane, is phase locked with the forced flapping motion of the foil, in agreement with previous flow visualisations