Figure 8.

A frame format of interactions among vortices, induced flow and hydrodynamic forces when maximum resultant fluid forces occurred. V expresses the relative velocity vector towards a hand, and the angle of attack (α) was equivalent to approximately 80°. When the hand starts at such a high angle of attack, the rapidly increasing circulation does not remain bound to the hand but rather forms an attached vortex on the leading edge. As swimming proceeds, the leading-edge vortex is eventually shed from the hand. This shedding is known as Von Karman vortex shedding, and its magnitude of circulation is denoted by Γ. The shedding vortex induces a jet flow between the dorsal side of the hand and the vortex, which further re-attaches to the thumb side vortex. By Kelvin’s circulation theorem, the magnitude of circulation about the attached vortex on the dorsal side increases with an increasing negative value of the shedding vortex (−Γ). In consequence, the pressure in the dorsal side declines drastically (Takagi et al., 2013).