Numerical study of the thunniform mode of fish swimming with different Reynolds number and caudal fin shape

The hydrodynamics of a model-fish swimming in thunniform mode was studied numerically in this paper. A ‘tuna’-like configuration and the undulating manner (the kinetics of swimming) were adopted from some references. The unsteady incompressible RANS equations were solved by an unsteady flow solver based on dynamic hybrid grids, which was developed by the authors in previous work. During the simulations, two typical turbulence models (SA-model and SST-model) were employed to investigate the turbulence effect, and compared with the ‘laminar’ case (switch off the turbulence models). The influence of Reynolds number was studied also. Numerical results demonstrate that the propulsion performance is better when considering turbulence models at higher Reynolds number, because the flow separation is relatively weaker than the ‘laminar’ cases. Furthermore, three types of caudal fin models were considered emphatically, including the popular crescent-shaped fin, a semicircle-shaped fin and a fan-shaped fin. Numerical results show that the crescent-shaped caudal fin is the most efficient when cruising, although the ‘thrust’ is relatively less. The main reason is that the energy loss in the lateral direction is less than those of the other two caudal fin models.

► The hydrodynamics of a model-fish swimming in thunniform mode is studied.
► The performance of three-types of caudal fin models is compared.
► The influence of Reynolds number and turbulence models is investigated.
► A vortex-ring structure is found in the wake during locomotion.
► The crescent-shaped caudal fin is found most efficient for cruising.