Effect of Flexibility of the Caudal Fin on the Propulsive Performance of Dolphins

In this paper, the effect of flexibility of the caudal fin on the propulsive performance of bottlenose dolphins is studied using the numerical simulation technique. The fluid-structure interactions are computed using an assumed mode method together with the 3D modified doublet lattice method (MDLM) and the 3D Navier-Stokes (NS) code. As the first step, the necessary power for the standing swimming condition is determined via numerical simulation using the 3D NS code. With this necessary power, the propulsive performance of horizontal swimming is estimated using the 3D MDLM coupled with an optimum design technique and the 3D NS code. The results show that the power-mass-ratio of the standing swimming is 62.2 W/kg which is approximately 2.6 times larger than that of human athlete, and it is an 11% decrease compared with that obtained under the rigid fin assumption. As to the horizontal swimming, the propulsive efficiency increases approximately 2–4% compared with that of the rigid fin to attain thesame amount of thrust according to the analysis using the 3D MDLM, while the analysis using the 3D NS code predicted an approximate 12% decrease in efficiency due to flow separation observed around the tip region. As the result of these analyses, the maximum speed of horizontal swimming is predicted to be 12 m/s which is a 1 m/s decrease from the 13 m/s estimated under the rigid fin assumption.