Swimming dynamics and propulsive efficiency of squids throughout ontogeny

Abstract

Squids encounter vastly different flow regimes throughout ontogeny as they undergo critical morphological changes to their two locomotive systems: the fins and jet. Squid hatchlings (paralarvae) operate at low and intermediate Reynolds numbers (Re) and typically have rounded bodies, small fins, and relatively large funnel apertures, whereas juveniles and adults operate at higher Re and generally have more streamlined bodies, larger fins, and relatively small funnel apertures. These morphological changes and varying flow conditions affect swimming performance in squids. To determine how swimming dynamics and propulsive efficiency change throughout ontogeny, digital particle image velocimetry (DPIV) and kinematic data were collected from an ontogenetic range of long-finned squid Doryteuthis pealeii and brief squid Lolliguncula brevis swimming in a holding chamber or water tunnel (Re = 20-20 000). Jet and fin wake bulk properties were quantified, and propulsive efficiency was computed based on measurements of impulse and excess kinetic energy in the wakes. Paralarvae relied predominantly on a vertically directed, high frequency, low velocity jet as they bobbed up and down in the water column. Although some spherical vortex rings were observed, most paralarval jets consisted of an elongated vortical region of variable length with no clear pinch-off of a vortex ring from the trailing tail component. Compared with paralarvae, juvenile and adult squid exhibited a more diverse range of swimming strategies, involving greater overall locomotive fin reliance and multiple fin and jet wake modes with better defined vortex rings. Despite greater locomotive flexibility, jet propulsive efficiency of juveniles/adults was significantly lower than that of paralarvae, even when juvenile/adults employed their highest efficiency jet mode involving the production of periodic isolated vortex rings with each jet pulse. When the fins were considered together with the jet for several juvenile/adult swimming sequences, overall propulsive efficiency increased, suggesting that fin contributions are important and should not be overlooked in analyses of the swimming performance of squids. The fins produced significant thrust and consistently had higher propulsive efficiency than did the jet. One particularly important area of future study is the determination of coordinated jet/fin wake modes that have the greatest impact on propulsive efficiency. Although such research would be technically challenging, requiring new, powerful, 3D approaches, it is necessary for a more comprehensive assessment of propulsive efficiency of the squid dual-mode locomotive system.

Aperture effects in squid jet propulsion

“…Because our focus was on the overall ecological importance of efficiency, we chose to consider whole-cycle efficiency, including both contraction and refilling phases of the jet cycle. Thus, our efficiency values are not comparable with those of studies that considered only the propulsive efficiency of the contraction phase (Bartol et al, 2008;Bartol et al, 2009a;Bartol et al, 2009b). Studies that considered whole-cycle efficiency have found values of 38-49% (Anderson and DeMont, 2000;Anderson and Grosenbaugh, 2005) for adult D. pealeii (22-30 cm ML) and 29.0-44.6% (Bartol et al, 2001) for juvenile and adult L. brevis (1.8-8.9 cm ML).…”

“…In general, squid face a range of Reynolds numbers from ~1 as paralarvae to ~10 8 as the largest adults (Bartol et al, 2008). How can the same swimming mechanism be used at all sizes?…”

Volumetric flow imaging reveals the importance of vortex ring formation in squid swimming tail-first and arms-first

“…The hydrodynamics of the squid jet have been well studied (Anderson and DeMont, 2000;Anderson and Grosenbaugh, 2005;Bartol et al, 2001bBartol et al, , 2008Bartol et al, , 2009aJohnson et al, 1972;O'Dor, 1988) but less is known about the hydrodynamics of the fins (Bartol et al, 2001b(Bartol et al, , 2008Stewart et al, 2010). In many of these studies, digital particle image velocimetry (DPIV) was used to provide quantitative data on jet and fin flows (Anderson and Grosenbaugh, 2005;Bartol et al, 2008Bartol et al, , 2009aStewart et al, 2010).…”

“…In many of these studies, digital particle image velocimetry (DPIV) was used to provide quantitative data on jet and fin flows (Anderson and Grosenbaugh, 2005;Bartol et al, 2008Bartol et al, , 2009aStewart et al, 2010). One limitation of DPIV, however, is that it can only quantify flows in one plane at a time.…”

Optimal vortex formation in a self-propelled vehicle

“…The presence of coherent vortical structures in the near-wake of a jet, hereafter referred to as 'vortex-enhanced propulsion', has been studied extensively and shown to increase propulsive performance in self-propelled vehicles (Siekmann 1962;Weihs 1977;Müller et al 2000a;Krueger 2001;Finley & Mohseni 2004;Choutapalli 2007;Bartol et al 2008;Krieg & Mohseni 2008, 2013Moslemi & Krueger 2010Ruiz, Whittlesey & Dabiri 2011). Weihs (1977, using many assumptions, analytically predicted an increase of 50 % in the average thrust through the use of vortex-enhanced propulsion.…”