In the nature, great deals of fish are living in the unsteady, dynamic flow regimes, such as the coral reefs in shallow marine ecosystems. In such a changeable ambient environment, fish can stay, prey and swim breezily. To reduce the perturbation of the complex flow around itself, fish have evolved a spectrum of different swimming modes and morphologies to reduce energy expenditure and improve swimming performance in these environments. Until now, the studies on the swimming motion of fish mainly focus on the steady flow environment, but the study on fish immersed in the oscillatory flow is scarce. In this paper, a 2-D slender body is constructed based on the horizontal section of fish in anguilliform swimming mode. The oscillatory flow past the wave slender body, which is used to model the undulatory body of fish swimming steadily, is studied. By varying the shape of the wave slender body, such as the wave length, the amplitude and the phase, the morphology of fish at different moment can be replicated. The hydrodynamic force and flow structure around the slender body are used to describe the characteristics of this issue. We found that, the tail morphology is the key point for the slender body to stay in the oscillating flow. The Keulegan-Carpenter number is important for the hydrodynamic characteristics around the slender body. For large Keulegan-Carpenter number, fish can remain stable easily by adjusting the morphology. For small Keulegan-Carpenter number, the fish should make a big move to keep hovering.
In the nature, great deals of fish are living in the unsteady, dynamic flow regimes, such as the coral reefs in shallow marine ecosystems. In such a changeable ambient environment, fish can stay, prey and swim breezily. To reduce the perturbation of the complex flow around itself, fish have evolved a spectrum of different swimming modes and morphologies to reduce energy expenditure and improve swimming performance in these environments.
