Swimming dolphins generate fully developed turbulence. In the present study, we demonstrate that the hierarchy of multiscale vortices existing in the turbulence is key to understanding how dolphins swim. For this demonstration, we conduct direct numerical simulations of a self-propelled dolphin using a simple model, and examine the role of multiscale vortices in propulsion. By decomposing the turbulent flow into different scales, we elucidate how the dolphin generates the hierarchy of multiscale vortices. Large vortex rings, which are shed due to the oscillation of the caudal fin, produce significant propulsion, while smaller vortices are created through the energy cascade, contributing little to the propulsion. We also demonstrate that the role of these vortices in the propulsion remains robust regardless of the Reynolds number.

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• Biomimetic & bio-inspired materials
• Swimming
• Turbulence
• Direct numerical simulations
• Immersed boundary methods
• Lattice-Boltzmann methods