Hydrodynamics in a diamond-shaped fish school*

In this paper, the computational fluid dynamics was applied to fish-like swimming, and the propulsion mechanism of this motion was focused. Although previous researchers have suggested that a diamond shape of fish school is helpful for drag reduction and efficiency enhancement, and individuals can benefit from such a school, experimental data or numerical studies on the hydrodynamics of interactions among members in the fish school are lacking. An improved immersed boundary method was employed for the simulations, and a basic element of three fishes was picked out from the diamond-shaped fish school. The conclusion is drawn that a fish situated laterally midway between two fish of the preceding column can benefit from the reversed Karman vortex street shedding from the upstream fish; and therefore the propulsion efficiency is increased, and the power consumed is reduced. Such a result accords well with the previous hypothesis.