Fig. 12. Fluid jet velocities associated with fluid motion out of the gap during wing motion preceding the clap, and fluid motion into the gap during fling phase. (A) Pictogram illustrating wing shape and the layers (as a % of R) used for digital particle image velocimetry (DPIV). (B) Temporal change of local vertical fluid velocities averaged along a line between the two trailing wing edges during clap-and-fling wing motion. Data were derived from DPIV images and show fluid velocities at five different distances to the wing base. A negative value means that the fluid is moving downwards in a vertical direction (downward jet). A positive value means that fluid is sucked around the trailing wing edges into the `v'-shaped cleft from below. Color coding as in A.