Abstract

Archer fish (genus Toxotes) exhibit multi-modal prey capture strategies combining spitting, rapid in-water pursuit, and jumping to feed in competitive environments. Archer fish can successfully jump to capture prey located several body lengths out of the water from directly below the surface with zero initial velocity. This rapid maneuver leaves limited space (one body length) to accelerate before fully exiting the water. The biomechanics and hydrodynamics of the fin and body motions for propelling, steering, and stabilizing the fish is highly three-dimensional and of interest to engineers aiming to replicate these aquatic launches. I will present results from 3D PIV studies on live jumping archer fish over a range of jump heights. Experiments focus on the interactions between three posterior fins (anal, dorsal, and caudal) and the role of these fins in stability and propulsion. The timing, interactions, and relative contributions to thrust and lateral forces from each fin show direct interactions between the upstream momentum generated by the anal and dorsal fins and the caudal fin in subsequent tail strokes. Time-resolved, volumetric measurements of the unsteady hydrodynamic wake structures are acquired using a light-field imaging and synthetic aperture refocusing methodology. The novel three-dimensional, three-component (3D-3C) light field particle imaging velocimetry (PIV) method uses a multi-camera array (Figure 1a) to resolve volumetric flow fields, from vortex rings to multiphase flows (e.g., Figure 1b). Light Field PIV system represents the next generation of 3D PIV techniques and can have significant impact on the community due to the relatively low cost of image reconstruction and the ability to resolve densely seeded flow fields, to image near deformed interfaces, such as the archer fish fins. Results from 3D PIV studies on live jumping archer fish over a range of jump heights will be discussed in the context of propulsive performance and jumping statistics.

Presenter Bio

Prof. Alexandra (Alex) Techet is an Associate Professor of Mechanical and Ocean Engineering, in the department of Mechanical Engineering at MIT. Prof. Techet received her B.S.E. in Mechanical and Aerospace Engineering in 1995 from Princeton University and then graduated from the MIT/WHOI Joint Program in Oceanographic Engineering with a M.S. in 1998 and a Ph.D. in 2001. Professor Techet was a recipient of the 2004 ONR Young Investigators Award and is a Fellow of the American Society of Mechanical Engineers. Her research in experimental hydrodynamics has made important contributions to several key areas, including: light field imaging for fluid mechanics, 3D multi-phase flow imaging, spray hydrodynamics, water entry of spheres and projectiles, flow structure interactions, unsteady bio-inspired propulsion and maneuvering, and sensing at the air/sea interface. Prof. Techet’s work provides critical insights for the design and understanding of a wide range of systems that operate in the marine environment, including surface ships, submarines, undersea projectiles, offshore oil platforms, and ocean energy systems.

Publication Date

11-2-2018

Document Type

Presentation

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