Meeting Abstract

54.1  Thursday, Jan. 6  Effect of Funnel Aperture Variation on Jet Dynamics of Squid BARTOL, I.K.; Old Dominion University, Norfolk, VA ibartol@odu.edu

Squids employ a dual mode propulsive system involving a pulsed jet and complex fin movements, both of which are capable of producing multiple wake modes. The two most prominent hydrodynamic jet modes observed during steady swimming in brief squid Lolliguncula brevis are: (1) jet mode I, where the ejected fluid rolls up into an isolated vortex ring for each jet pulse and (2) jet mode II, where the ejected fluid develops into a leading vortex ring that separates or “pinches off” from a long trailing jet for each pulse. Jet mode II produces greater time-averaged thrust and lift forces per pulse and is the jet mode most heavily used, but jet mode I is associated with higher propulsive efficiency, lower slip, and shorter jet periods. While it is known that the funnel diameter of squid varies throughout the jet pulse, with circular and radial muscles presumably playing important roles in funnel aperture closure and opening, the extent to which funnel aperture changes influence jet wake dynamics and propulsive performance has not been studied in squid. To investigate the possibility of performance optimization via funnel aperture variation, digital particle image velocimetry data of jet flows from actively swimming L. brevis were collected together with high-speed, high-resolution kinematic footage of the funnel and mantle. Results indicate that the timing of full aperture opening and constriction, together with mantle movements, can impact vortex structure and ring disconnection from the trailing jet, vortex circulation, and propulsive efficiency. Moreover, there are differences in funnel aperture control between arms-first and tail-first swimming that have important consequences for vortex dynamics and the generation of the two prominent jet modes.