Hydrodynamic analysis of rigid and flexible pectoral fins.

Numerical study on unsteady hydrodynamic characteristics of rigid and flexible pectoral fins in viscous flow-field was performed in the present study. The effect of key kinematical parameters on the propulsion performance was analyzed. The propulsion mechanism was explored by evolution of wake vortices. Computational results revealed that optimal combination for investigated parameters was U = 4C, Φ(FLA) = 45°, ΔΦ(FL) = 60° and α(0) = 0.2. Wake vortices were shed from two edges of fin and fin tip and convect downstream as well as laterally. For flexible pectoral fin, the shedding time was delayed and shed wake vortices keep longer time near the fin that led to difference in variation amplitude of hydrodynamics as compared to rigid fin. The hydrodynamic performance of flexible fin was superior to that of rigid fin for low incoming velocity. However, the opposite situation occured for high incoming velocity.