Fig. 5. DSPIV result of the 3-D flow structures and evolution of the vortices on the model wing at three typical stroke phases. The left and right image sequences are viewed from two perspectives. Isosurfaces of the Q-value are plotted to educe the vortices. The normalized values of the external red and internal yellow isosurfaces are 0.09 and 0.36, respectively. Lp, the primary vortex; Lm1, Lm2 and Lm3, the minor vortices; T1 and T2, trailing-edge vortices (TEVs); Tr, the root of TEV; W1 and W2, wing-tip vortices (WTVs). The thick yellow curved arrows denote the rotational directions of the vortices. The white instantaneous streamlines in Lp in all images are spiraling towards the wing-tip; the magenta (released at the wing-tip) and yellow (released at the outer wing within Lm2) streamlines in 0.25T are heading towards the wing-base and meet the white streamlines at the breakdown location of Lp; the green streamlines belong to the WTVs.