Fluid-structure investigation of a squid-inspired swimmer

Abstract

We propose a novel underwater propulsion system inspired by the jet-propelled locomotion mechanism of squids and other cephalopods. A two-dimensional nonaxisymmetric fluid-structural interaction model is developed to illustrate the physical mechanisms involved in the propulsive performance of this design. The model includes a deformable body with a pressure chamber undergoing periodic inflation and deflation motions enabled by attached springs and a nozzle through which the chamber is refilled and discharged (to form a jet). By using an immersed-boundary algorithm, we numerically investigate the dynamics of this system in the tethered mode. The thrust generation is found to increase with the frequency of body deformation, whereas the efficiency reaches a peak at a certain frequency. Examinations of the surrounding flow field illustrate a combination of vortices shed from the body and the nozzle. The optimal efficiency is reached when the nozzle-generated vortices start to dominate the wake. Our simulations also suggest that steady-state response can only be sustained for a few cycles before the wake is disturbed by a symmetry-breaking instability, which significantly affects the propulsive performance. Special strategies are needed to achieve stable long-distance swimming.

Pulsed-jet propulsion of a squid-inspired swimmer at high Reynolds number

“…Extensive advances in understanding propulsive mechanics derived from jellyfish models were summarized in a recent review paper (Costello et al, 2020). Nevertheless, as suggested by Bi and Zhu (2019b), it is not appropriate to apply the knowledge from jellyfish swimming to squids directly due to some critical differences Water Jet (b) 3 between them. Specifically, jellyfish mainly rely on bell constriction to swim.…”

“…They do not have a well-formed pressure cavity and a funnel which serves as a nozzle to separate the internal and external flows. Since jellyfish have limited capability to compress the entrained fluid, the jet flow they create is much weaker, and the instability issue may not be as pronounced as in the squid-created wake (Bi and Zhu, 2019b). Besides, different body geometry and kinematics also yield different vorticity control mechanism, which can be found from the comparison between Hoover and Miller (2015) and Bi and Zhu (2019b).…”

“…Following these studies, a series of numerical simulations have been conducted by Bi and Zhu (2018, 2019a, 2019b to understand the combined effect of jetting and body deformation.…”

“…By using a three-dimensional boundary-element method, they investigated the burst-coast swimming of a cephalopod-like deformable body with a pressure chamber. Two-dimensional fluid-structure interaction (FSI) model based on the immersed-boundary framework was developed subsequently to study the fully-viscous response of the squid-like jet propulsion system activated by a sequence of springs in tethered (Bi and Zhu, 2019b) and free-swimming (Bi and Zhu, 2019a) modes under low Reynolds number conditions. Symmetry-breaking instability and effect of added-mass on the jet propulsion were demonstrated.…”

Computational Model Construction and Analysis of the Hydrodynamics of a Rhinoptera Javanica

“…Breder [4] has classified the swimming modes into the body and/or caudal fin (BCF) mode and median and paired fin(MPF) mode. Many studies have been focused on BCF modes [5]- [9] which are associated with drag-based propulsion. Different from the BCF mode, MPF mode is associated with lift-based propulsion.…”