Hydrodynamic role of longitudinal dorsal ridges in a leatherback turtle swimming.

Kyeongtae Bang,Jooha Kim,Sang-Im Lee,Haecheon Choi

doi:10.1038/srep34283

Abstract

Leatherback sea turtles (Dermochelys coriacea) are known to have a superior diving ability and be highly adapted to pelagic swimming. They have five longitudinal ridges on their carapace. Although it was conjectured that these ridges might be an adaptation for flow control, no rigorous study has been performed to understand their hydrodynamic roles. Here we show that these ridges are slightly misaligned to the streamlines around the body to generate streamwise vortices, and suppress or delay flow separation on the carapace, resulting in enhanced hydrodynamic performances during different modes of swimming. Our results suggest that shapes of some morphological features of living creatures, like the longitudinal ridges of the leatherback turtles, need not be streamlined for excellent hydro- or aerodynamic performances, contrary to our common physical intuition.

Highlights

Leatherback sea turtles (Dermochelys coriacea), the largest and the deepest diver among marine turtles, are known to have superior diving ability[1,2,3]
We constructed carapace models of a leatherback turtle with and without the longitudinal ridges, and conducted force and velocity measurements to investigate the hydrodynamic roles of the ridges in different modes of swimming of the leatherback turtles
Our results suggest that the hydrodynamic performance can be enhanced by the ridges in the V-shaped diving where lift generation is required due to negative buoyancy during most of their ascent

Summary

Introduction

Leatherback sea turtles (Dermochelys coriacea), the largest and the deepest diver among marine turtles, are known to have superior diving ability[1,2,3]. Measurements were performed at two conditions, α =−22° and Re = 2 × 105, and α = 18° and Re = 5 × 105, that are characteristic of the vigorous swimming of hatchlings and the active ascending swimming of adults, respectively (see Methods (Flow-field measurements) and Supplementary Fig. S5 for the experimental setup).

Results

Conclusion