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] 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 ) 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.

Archer fish jumping prey capture: kinematics and hydrodynamics

“…Flammang et al, 2011;Mendelson and Techet, 2015;Bartol et al, 2016;Murphy et al, 2016). These techniques provide the ability to simultaneously analyze all fins involved during jumping.…”

“…Mendelson and Techet (2015) showed that assumptions regarding symmetry and the alignment of a wake structure with the light sheet can lead to miscalculation of the momentum in a complex 3D fish wake with interacting flow structures. Volumetric calculation of wake energy as in Bartol et al (2016) could further be directly compared with the ballistic energy of the fish. The kinetic energy of individual fins during the thrust production stage, energy used to deform the free surface and changes in the fluid pressure field surrounding the fish must also be considered to perform complete mechanical energy accounting during a jump.…”

New approaches for assessing squid fin motions: Coupling proper orthogonal decomposition with volumetric particle tracking velocimetry

“…Movements ranging from simple flapping to multi-wave, bi-directional undulations have been observed in squid (Anderson and DeMont, 2005;Bartol et al, 2001b;Hoar et al, 1994;Vecchione et al, 2001Vecchione et al, , 2002. This range of motion provides propulsive and control benefits that complement the vectored jet system, as demonstrated in cruising, maneuverability and predatorattack studies (Bartol et al, 2016.…”

“…The hydrodynamics of the pulsed jet have been studied in several species of neritic and oceanic squids (Anderson and DeMont, 2000;Anderson and Grosenbaugh, 2005;Bartol et al, 2001bBartol et al, , 2008Bartol et al, , 2009aBartol et al, ,b, 2016Johnson et al, 1972;O'Dor, 1988), but much less is known about the hydrodynamics of the other propulsive component in this dual-mode system, namely the fins (but see Bartol et al, 2016;Stewart et al, 2010). Fin morphology and function vary widely among squids.…”

Experimental Measurement of Dolphin Thrust Generated during a Tail Stand Using DPIV

“…The orientation within the bubble curtain was important in limiting three-dimensional effects. Such three-dimensional considerations may be dealt with in future tests with the application of volumetric DPIV as used to study swimming by fish and squid [36][37][38].…”