Jet flow in steadily swimming adult squid

Abstract

SUMMARY Although various hydrodynamic models have been used in past analyses of squid jet propulsion, no previous investigations have definitively determined the fluid structure of the jets of steadily swimming squid. In addition, few accurate measurements of jet velocity and other jet parameters in squid have been reported. We used digital particle imaging velocimetry (DPIV) to visualize the jet flow of adult long-finned squid Loligo pealei(mantle length, Lm=27.1±3.0 cm, mean ± s.d.) swimming in a flume over a wide range of speeds(10.1-59.3 cm s-1, i.e. 0.33-2.06 Lms-1). Qualitatively, squid jets were periodic, steady, and prolonged emissions of fluid that exhibited an elongated core of high speed flow. The development of a leading vortex ring common to jets emitted from pipes into still water often appeared to be diminished and delayed. We were able to mimic this effect in jets produced by a piston and pipe arrangement aligned with a uniform background flow. As in continuous jets, squid jets showed evidence of the growth of instability waves in the jet shear layer followed by the breakup of the jet into packets of vorticity of varying degrees of coherence. These ranged from apparent chains of short-lived vortex rings to turbulent plumes. There was some evidence of the complete roll-up of a handful of shorter jets into single vortex rings, but steady propulsion by individual vortex ring puffs was never observed. Quantitatively, the length of the jet structure in the visualized field of view, Lj, was observed to be 7.2-25.6 cm, and jet plug lengths, L, were estimated to be 4.4-49.4 cm using average jet velocity and jet period. These lengths and an average jet orifice diameter, D, of 0.8 cm were used to calculate the ratios Lj/D and L/D, which ranged from 9.0 to 32.0 and 5.5 to 61.8, respectively. Jets emitted from pipes in the presence of a background flow suggested that the ratio between the background flow velocity and the jet velocity was more important than L/D to predict jet structure. Average jet velocities in steadily swimming squid ranged from 19.9 to 85.8 cm s-1 (0.90-2.98 Lm s-1) and were always greater in magnitude than swimming speed. Maximum instantaneous fluid speeds within squid jets ranged from 25.6 to 136.4 cm s-1. Average jet thrust determined both from jet velocity and from three-dimensional approximations of momentum change in successive jet visualizations showed some differences and ranged from 0.009 to 0.045 N over the range of swimming speeds observed. The fraction by which the average jet velocity exceeded the swimming speed, or `slip',decreased with increasing swimming speed, which reveals higher jet propulsive efficiency at higher swimming speeds. Jet angle, subtended from the horizontal, decreased from approximately 29° to 7° with increasing swimming speed. Jet frequency ranged from 0.6 to 1.3 Hz in the majority of swimming sequences, and the data suggest higher frequencies at the lowest and highest speeds. Jet velocity, angle, period and frequency exhibited increased variability at speeds between 0.6 and 1.4 Lms-1. This suggests that at medium speeds squid enjoy an increased flexibility in the locomotive strategies they use to control their dynamic balance.

Ultra-fast escape of a deformable jet-propelled body

“…Our model for the propelling jet flow was also greatly simplified, prescribing a constant-magnitude uniform-profile jet and not solving for the internal cavity flow. Hence no attention was paid to optimizing the jet flow, an important problem in itself (Linden & Turner 2004;Anderson & Grosenbaugh 2005;Bartol et al 2009;Moslemi & Krueger 2011). Also, there is a connection of the present work to the hydrodynamics of medusae (Dabiri, Colin & Costello 2006), particularly when the mode of 'umbrella' deflation G. D. Weymouth and M. S. Triantafyllou is assumed; for this problem, the interaction of the flow around the body with the jet flow is significant, and could provide further, potentially beneficial, effects.…”

Structural Dynamics of a Pulsed-Jet Propulsion System for Underwater Soft Robots

“…This vehicle weighs 335 g, has a mantle maximum extension in the axial direction of 16 cm and a mantle capacity of 35 ml, was found [32] coincident with the peak of swimming efficiency. As for the Octopus vulgaris, i.e., the common octopus, specimen are found to grow to a mantle length of about 25 cm and swim at an average speed of 0.18 m/s, which is 0.7 bdl/s.…”

Form, function and flow in the plankton : jet propulsion and filtration by pelagic tunicates

“…These ranges extend well above 3.6-4.5 and since co-flow reduces optimum F, squid jet events are frequently elongated plugs of fluid rather than discrete vortex rings (Anderson and Grosenbaugh 2005). Variation in jet diameter by Nemiopsis bachei , a cnidarian jellyfish species that swims by jet propulsion, led to a maximum F of around 8, and vortex ring pinch-off never occurred (Dabiri et al 2006).…”

“…Pipe jet experiments and studies with jet-propelled organisms have shown that the optimum F can be affected by at least two phenomena: 1) background co-flow can lower the optimum F due to early pinch-off or inhibition of vortex rings, leading to elongated jets with weak or absent vortex rings (Anderson and Grosenbaugh 2005) and 2) variation in jet diameter and/or jet velocity can delay pinch off . The jets of steadily swimming squid, which always experience co-flow due to flow past the squid occur at formation numbers of F = 5.5-61.8 (adult Loligo pealei) and F = 3.23-23.19 (juvenile and adult Lolliguncula brevis) Grosenbaugh 2005, Bartol et al 2009).…”