Three-dimensional viscous wake flow in fish swimming - A CFD study

Abstract

In the present paper, the assessment of the hydrodynamics of fish swimming wake-flow is carried out to identify the main features related to the propulsion performance. Two different fish models with caragiform kinematics are studied: tuna fish (Thunnus atlanticus) and lambari (Astyanax bimaculatus). CFD methods were used to simulate laminar and turbulent flow regimes and a dynamically adaptive mesh discretization (ALE) was employed to reproduce fish motion. Simulations were run in a typical range of Reynolds (Re) and Strouhal (St) numbers of the fish swimming flow investigating hydrodynamics forces and the flow patterns of the induced fish-swimming wake. Firstly, equilibrium condition (drag balancing thrust) for Strouhal was achieved for each Reynolds number and three-dimensional wake structures were evaluated concluding that fish swimming experiencing a forward locomotion movement with a reversal von-Kármán vortex street and a high-velocity jet through the downstream direction. Finally, vorticity dynamics analysis showing that the leading-edge vortex produced by the caudal fin is associated to the peak of thrust in the motion cycle.