Hydrodynamics of frontal striking in aquatic snakes: drag, added mass, and the possible consequences for prey capture success

Marion Segall (1, 2, 3) , Anthony Herrel (4, 1) , Ramiro Godoy-Diana (2)

1 MECADEV - Mécanismes Adaptatifs et Evolution
2 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)
3 AMNH - American Museum of Natural History [New York, USA] = Musée américain d'histoire naturelle [New York, USA]
4 Evolutionary Morphology of Vertebrates

Transient locomotion under water is highly constrained by drag and added mass, yet some aquatic snakes catch their prey using a fast forward acceleration, with the mouth opened. These aquatic snakes show a convergence of their head shape in comparison with closely related species that do not forage under water. As both drag and added mass are related to some extent to the shape of the moving object, we explored how shape impacts the hydrodynamic forces applied to the head of a snake during a prey capture event. We compared two 3D-printed heads representing typical shapes of aquatically-foraging and non-aquatically-foraging snakes, and frontal strike kinematics based on in vivo observations. By using direct force measurements, we calculated the drag and added mass coefficient of the two models. Our results show that both drag and added mass are reduced in aquatic snakes. The drag coefficient of the aquatic model is 0.24, which is almost two times smaller than the non-aquatic model. The added mass coefficient of the aquatic model is 0.15 versus 0.24 for the non-aquatic model, showing that the convergence of head shape in aquatically foraging snakes is associated with a hydrodynamic advantage during frontal striking. The vorticity field measurements with particle image velocimetry show that a less intense recirculation bubble behind the jaw of the aquatic model, compared to the non-aquatic model, might be the basis of this advantage

Mots clés: Snakes; Fluid mechanics; Forces; Morphology; Transient motion

Domaines: Biomécanique [physics.med-ph]; Zoologie des vertébrés; Mécanique des fluides [physics.class-ph]

Marion Segall, Anthony Herrel, Ramiro Godoy-Diana. Hydrodynamics of frontal striking in aquatic snakes: drag, added mass, and the possible consequences for prey capture success. Bioinspiration and Biomimetics, 2019, 14 (3), pp.036005. ⟨10.1088/1748-3190/ab0316⟩. ⟨hal-02105744⟩