The three-dimensional hydrodynamics of thunniform swimming under self-propulsion

摘要

This paper presents the hydrodynamics of thunniform swimming under self-propulsion as the body and caudal fin kinematic behaviors are systematically varied. The swimmer is a three-dimensional (3D) tunalike flexible model with prescribed kinematics of thunniform mode. Simulations are carried out for various body behaviors by varying the wave frequency f and the tail amplitude A(p) and for various caudal fin behaviors by varying the maximum angle of attack alpha(max) and the phase difference phi. The results show that the swimming velocity as well as the propulsive efficiency is an increasing function of both f and Ap, but their trend with am.. and phi is found to be not monotonic. Specially, for peak swimming velocity generation, alpha(max) occurs at 20-30, and phi, ranges from 60 to 75, while for peak efficiency, alpha(max) is 20-30 and phi nears 90 degrees. The wake structure formed by the swimmer is single row wake consisting of a series of disconnected vortex rings that are resembled by sickle-like shape vortices. As phi increases, the tail of the sickle-shape vortices is shortening gradually while the head is stretching. As amax increases, the aligned sickle-like vortices have almost identical shape with each other, but the wake strength is reducing gradually. (c) 2015 Elsevier Ltd. All rights reserved.