Two-phase flow large-eddy simulations of jumping archer fish hydrodynamics and aerodynamics using detailed motion kinematics

The archer fish’s impulsive vertical jumping behavior is associated with rapid upward thrust, produced from an initial stationary position below the free surface, followed by gliding. We herein integrate detailed jump body and fin kinematics with two-phase flow large-eddy simulations to investigate the hydrodynamics of oscillatory body kinematics and the aerodynamics of C-shaped body bending after water exit. Our simulations enable accurate prediction of forces exerted by the fish and elucidate the emergence of intricate 3D vortical structures. In water, we investigate the effect of the Reynolds and Strouhal numbers, which cannot controllably vary in experimental studies on live archer fish, on the shape, size and strength of the emerged turbulent coherent structures. We further compare the vortex loops generated by the caudal fin during in-water oscillatory motion. Braided hairpins, whose heads and legs appear to have similar thickness, constitute patterns that are also found in the wake of in-water C-start accelerations. Rich vortical structures and square-shaped vortex rings are formed after the fish leaves the water.