title: Volumetric flow imaging reveals the importance of vortex ring formation in squid swimming tail-first and arms-first.
abstract: Squids use a pulsed jet and fin movements to swim both arms-first (forward) and tail-first (backward). Given the complexity of the squid multi-propulsor system, 3D velocimetry techniques are required for the comprehensive study of wake dynamics. Defocusing digital particle tracking velocimetry, a volumetric velocimetry technique, and high-speed videography were used to study arms-first and tail-first swimming of brief squid Lolliguncula brevis over a broad range of speeds [0-10 dorsal mantle lengths (DML) s(-1)] in a swim tunnel. Although there was considerable complexity in the wakes of these multi-propulsor swimmers, 3D vortex rings and their derivatives were prominent reoccurring features during both tail-first and arms-first swimming, with the greatest jet and fin flow complexity occurring at intermediate speeds (1.5-3.0 DML s(-1)). The jet generally produced the majority of thrust during rectilinear swimming, increasing in relative importance with speed, and the fins provided no thrust at speeds >4.5 DML s(-1). For both swimming orientations, the fins sometimes acted as stabilizers, producing negative thrust (drag), and consistently provided lift at low/intermediate speeds (<2.0 DML s(-1)) to counteract negative buoyancy. Propulsive efficiency (η) increased with speed irrespective of swimming orientation, and η for swimming sequences with clear isolated jet vortex rings was significantly greater (η=78.6±7.6%, mean±s.d.) than that for swimming sequences with clear elongated regions of concentrated jet vorticity (η=67.9±19.2%). This study reveals the complexity of 3D vortex wake flows produced by nekton with hydrodynamically distinct propulsors.
authors.affiliation: Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA ibartol@odu.edu.
authors.forename: Ian K
authors.initials: IK
authors.lastname: Bartol
authors.affiliation: Department of Mechanical Engineering, Southern Methodist University, Dallas, TX 75275, USA.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Krueger
authors.affiliation: Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Jastrebsky
authors.affiliation: Department of Mechanical Engineering, Southern Methodist University, Dallas, TX 75275, USA.
authors.forename: Sheila
authors.initials: S
authors.lastname: Williams
authors.affiliation: Department of Biology, Franklin and Marshall College, Lancaster, PA 17604, USA.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Thompson
mesh_terms: D058500:Animal Fins / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D049832:Decapodiformes / Q000502:physiology*; D012212:Rheology; D013550:Swimming; D014741:Video Recording
keywords: Cephalopod; Fin motion; Jet propulsion; Volumetric velocimetry; Wake dynamics