Several fish species like tunafish propel by oscillating the tail as a flapping foil, while the remaining part of the body essentially contributes to the overall drag. Since in this case thrust and drag are in a way separable, being given by different parts of the fish's body, most of the attention was focused in the past on the study of a flapping foil under a prescribed stream and on its propulsive efficiency.
On the other hand for undulatory fish, whose drag and thrust are severely entangled and hardly separable, the self-propelled locomotion approach has been largely recognized as the main path to be followed to obtain meaningful results, hence the propulsive efficiency loses its meaning and has to be replaced by the cost of transport as a measure of the swimming performance.
By using a simple inviscid numerical method, properly assessed by a viscous solver, the intention is to study the self-propelled swimming mode and the performance for cruising motions of an oscillatory two-dimensional swimming fish, with the aim to highlight the differences with the prescribed stream approach in determining the optimal swimming conditions.
Nowadays there is an increasing interest in bio-inspired forms of propulsion. Among others, a large number of efforts are shown by experimentalists, biologists and computational scientists to design self-propelled robotic fish with the aim to study the propulsive and maneuvering capabilities of real fish that are, to date, not yet fully understood.
In particular, several fish species propel by oscillating the tail, while the remaining part of the body essentially contributes to the overall drag. To simplify the study of such complicated problem, most of the attention was focused in the past on the flapping tail, represented by an airfoil, under a prescribed stream and on its propulsive efficiency. However, the swimming speed should be the result of the fish's interactions with the surrounding fluid, so fixing it may somehow affect the results.
A numerical study through a simplified model may shed some light on the effect of self-propulsion on the performance of oscillating swimming fish. For instance, the self-propelled approach leads to the evaluation of the cost of transport as the primary measure for the optimal range of the locomotion speed, which may differ markedly from the optimum swimming condition provided by the prescribed stream approach.
This research aims to extend the understanding of flapping tail propulsion with the perspective of developing a self-propelled robotic fish.