Three-dimensional flow measurements on flapping wings using synthetic aperture PIV

We present the results of 3D velocity measurements of the flow fields around a free-flying painted lady butterfly (Vanessa cardui) and a tethered mechanical flapper using Synthetic Aperture PIV (SAPIV). The velocity fields presented for the free-flying butterfly have limited spatial resolution; however, leading edge vortices (LEV) and trailing edge vortices (TEV) can be seen during the downstroke of the butterfly. The results show that SAPIV has potential as a flow analysis tool to obtain whole-field, time-resolved velocities surrounding freely flying insects. The results of a tethered mechanical flapper focus mainly on the LEV and TEV through an entire flapping cycle. The results are compared to velocity measurements taken using traditional PIV techniques. Additionally, force measurements of the lift and thrust generated by the mechanical flapper are compared with the calculated forces from the measured velocity data and circulation in the flow field. The reconstructed visual hull of the butterfly and mechanical flapper is also discussed.