Fig. 15. Streamlines of fluid flow around two wings (A) and around one wing (B) during a full clap and fling stroke at a Reynolds number (Re) of 8 and around two wings at Re=128 (C). The arrow on the left wing shows the direction of the normalized force acting on the wing. (A) During translation, leading and trailing edge vortices form and remain attached to the wing (i–iii). During `clap', the wings rotate together at the end of translation (iv–v). At this time, the leading and trailing edge vortices are shed. During `fling', the wings rotate apart forming two new leading edge vortices (vi). Towards the end of rotation, the wings are translated apart at a constant angle of attack and speed (vi–viii). During translation, the leading edge vortices remain attached to the wing, and weak trailing edge vortices are formed. (B) Large leading and trailing edge vortices are formed during the initial translation of the wing (i–iii). This pair of vortices is shed during rotation (iv–v), and a new pair of leading and trailing edge vortices is formed during the subsequent translation (vi–viii). Note that in the two winged case, no trailing edge vortices are formed during wing rotation, and much smaller trailing edge vortices are formed during the subsequent translation. (C) At Re=128, leading edge vortices are formed and the trailing edge vortices are shed (i–iii). After a translation of about 2.5 chord lengths, the leading edge vortices begin to separate from the wings (iii). During `clap', the wings rotate together at the end of translation (iv–v). At this time, the leading and trailing edge vortices are shed. During `fling', the wings rotate apart. Two large leading edge vortices are formed, and no trailing edge vortices are formed initially (v–vi). Towards the end of rotation, the wings are translated away from each other and the pair of leading edge vortices formed during rotation is shed. A second pair of leading edge vortices begins to form near the end of translation (vi–viii).