The design issues associated with underwater vehicles operating in the surf zone or other high-energy environments are likely to have viable biomimetic solutions. Fish, combining awesome maneuverability with the flow-sensing lateral line, can reduce energy expenditure through interaction with environmental vorticity. Rainbow trout (Oncorhynchus mykiss) swimming within a flow channel voluntarily positioned themselves 4D downstream from a 2" D-section cylinder, and synchronized with the cylinder wake in both frequency and phase. An electromyographic study of the axial muscle illustrated a significant reduction in activity while the trout was entraining behind the cylinder, as opposed to swimming within the free stream. A euthanized trout passively synchronized with the wake and accelerated forward towards the cylinder, through fluid-excited motion only, proving that trout benefit not only from drafting in the velocity deficit behind the cylinder, but also through interaction with the vortices in the wake.
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