Massachusets

An Introduction to Vortices and Vorticity - vortex.pdf

Prof. A.H. Techet
Department of Ocean Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139

To better understand the fluid forcing produced by fish when they are swimming it is necessary to first discuss the basic concept of a vortex and vorticity. A vortex arises when flow encircles a central point. Examples of where vortices occur in nature include: whirlpools, tornados, ocean eddies, blood flow through heart valves, and flow swirling behind rocks in a river current. Vortices appear in engineering fluid applications as well: flow around offshore platforms, tip-vortices from aircraft wings, helical vortices in propeller wakes and helicopter rotors. In general, vortices can form when flow passes any object with a non-streamlined shape or a sharp corner, and separates from the body.

Part 1B Engineering: Biological and Medical Engineering, Fish Swimming, Lecture 1 -2 - Trout_propulsion.pdf

..."Evidence suggests that many fish exploit the natural instability of the flow energetics to assist them in propulsion and maneuvering. By tuning their own kinematics, the fish is able to swim efficiently, to generate large thrust and turning forces, and to move silently through the flow with minimal wasted energy...."
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