Fig. 12. (A–E) Vorticity plots at three spanwise locations at various times during one stroke (symmetrical rotation). r1, r2 and r3 denote locations at 0.75, 0.5 and 0.25 wing lengths from the wing root, respectively. 
, non-dimensional time; 
, angle of attack. The magnitude of the non-dimensional vorticity at an outer contour is 1. Starting from the outer contour, for the first 21 contours, the contour interval is 0.2, for the next 30 contours, the contour interval is 0.5, and for the reminder of the contours, the contour interval is 5.
