Visualising coherent vortices generated by a swimming dolphin

We visualise the hierarchy of coherent vortices generated by a freely swimming dolphin, obtained from direct numerical simulations at a high Reynolds number. The visualisations are based on isosurfaces of the second invariant of the velocity gradient tensor evaluated from scale-decomposed velocity fields. We describe in detail the scale-decomposition procedure and the polygon-based visualisation, which enables the rendering of the data despite their large size. We also emphasise that visualising the hierarchy of coherent vortices clarifies the physical mechanism of dolphin propulsion, and more generally, provides physical insight into turbulence around swimming and flying organisms.