Effects of the structural relationships between the fish body and caudal fin on the propulsive performance of fish. (15th August 2019) - Zhao, Zhijie
Abstract: Two-dimensional numerical simulations are used to investigate the influence of a fish-like undulating foil on the hydrodynamic performance of a flapping rigid foil. The simulations are conducted to model the interplay between the flapping caudal fin and the undulating fish body in a virtual swimming tuna fish. Firstly, simulations about the pure heave motion and the combined heave and pitch motion of a rigid NACA0012 foil are performed. The simulation results agree well with the literature values. Then, the effects of structural configuration and spatial distance between the undulating foil and the flapping foil on the propulsive performance are studied. Numerical simulation results show that with a suitable structure, a disconnected structural configuration can dramatically improve the thrust and propulsive efficiency of the hind flapping foil compared with the connected structural configuration. In addition, a sudden degradation phenomenon of the hydrodynamic coefficients in the disconnected structural configuration at high Strouhal number ( St ) is investigated. This sudden degradation phenomenon can be eliminated completely with a better separation distance condition, and thus result in a better thrust increase. Highlights: A combined fish model is used to study the effect of structural relationship between fish body and caudal fin on swimming. A assumption is proposed that a distinctly separated tail is helpful to improve the propulsive performance. A sudden fluctuation phenomenon of the instantaneous hydrodynamic coefficients of the caudal fin is investigated in detail.