Measuring the 3D wake of swimming snakes (Natrix tessellata) using volumetric particle image velocimetry

Abstract

We describe a method for measuring the 3D vortical structures produced by an anguilliform swimmer using volumetric velocimetry. The wake of freely swimming dice snakes (Natrix tessellata) was quantified, revealing the creation of multiple vortices along the body of the snake due to its undulation. The 3D structure of the vortices generally consisted of paired vortex tubes, some of which were linked together to form a hairpin structure. The observations match predictions from computational fluid dynamic studies of other anguilliform swimmers. Quantitative measurements allowed us to study vortex circulation and size, and global kinetic energy of the flow, which varied with swimming speed, vortex topology, and individual characteristics. Our findings provide a baseline for comparing wake structures of snakes with different morphologies and ecologies and investigating the energetic efficiency of anguilliform swimming.

Functional diversity of snake locomotor behaviors: A review of the biological literature for bioinspiration

“…[61][62][63][64][65] A few studies have provided data on biomechanics and muscle activation patterns for snake undulatory swimming, also known as anguilliform swimming, which involves the propagation of a lateral traveling wave down the entire body, the amplitude of which increases from the head to the tail. 46,[66][67][68][69][70][71][72] Note that those looking to design an undulatory swimmer would do well to also examine the literature on other elongate animals, especially eels and lampreys; after all, the eel genus Anguilla lent its name to the term "anguilliform swimming." Despite the superficial similarity of undulatory swimming and terrestrial lateral undulation, they differ in aspects of their kinematics and underlying muscle activity (for a detailed discussion, see Refs.…”