CFD Simulation of Effect of Vortex Ring for Squid Jet Propulsion and Expeiments on a Bionic Jet Propulsor

Abstract

Using jet propulsion, squid can swim at high speed or at low speed with good maneuverability, which makes them quiet valuable to be studied for biomimetic purposes. Vortex rings usually occur in the highly-unsteady jet flow in squid, and they play quite important roles in the jet propulsion of squid. This paper tries to investigate the squid jet structure by computational fluid dynamics (CFD) analysis. A simplified squid body model was established. The mantle motion during jet locomotion was explicitly included into the simulations by using a deforming mesh. By solving the 2D-axisymmetric, incompressible, laminar, unsteady Navier–Stokes equations, different vortex evolution behaviors were observed depending on different mantle contraction velocities and nozzle diameters. An important parameter, the formation number of the vortex rings, L/D, which decide the propulsive efficiency of jet propulsion directly, was also discussed in this paper. The numerical results show that adult squid propel themselves by long jet flows with a large formation number, L/D. The results also prove that smaller squid have larger relative funnel diameter. Interaction of vortex rings was simulated in two jet process, which might interpret squid increase their contraction frequencies with elevated swimming speed. To validate the force generated in the simulation, a bionc squid mantel jet propulsor is investigated and tested.