Figure 8.

Particle image velocimetry images of the wake shed by dorsal fin and its flow over peduncle and caudal fin (large blue arrows). (A) Flow encountered by the peduncle and caudal fin is greatly modified by the dorsal and anal fins, and differs significantly from the free stream. (B,C) When the dorsal fin leads the caudal fin by 90°, the angle of attack of the dorsal shed wake relative to the caudal fin is relatively small. (E,F) In contrast, the angle of attack of the dorsal shed wake relative to the caudal fin is much larger when the dorsal fin lags the caudal by 90°. (D) Appropriate timing of the dorsal and anal fins relative to the peduncle and caudal fin aligns the shed wake with the caudal fin encouraging the production of a strong leading-edge vortex (LEV), with velocity vectors (yellow arrows) and vorticity plotted in blue and red.