Eddies
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- Glossary of hydrology, 1998:eddy (a circular movement of water that is generally in a different direction from that of the main current; it is a temporary current, usually formed at a point at which a current passes some obstruction, or between two adjacent currents flowing in opposite directions (cf: whirlpool, maelstrom); whirlpool (a body of water moving rapidly in a circular path of relatively limited radius (cf: eddy; maelstrom))
- Eapen, P.K. Elsevier's dict. of fisheries, 1999:eddy (1. wind or water moving in a curved or circular direction; 2. current or water running in a direction contrary to that of a tidal stream; whirlpool (current that has a rotary motion over a comparatively small area))
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid behind the obstacle flows into the void creating a swirl of fluid on each edge of the obstacle, followed by a short reverse flow of fluid behind the obstacle flowing upstream, toward the back of the obstacle. This phenomenon is naturally observed behind large emergent rocks in swift-flowing rivers. An eddy is a movement of fluid that deviates from the general flow of the fluid. An example for an eddy is a vortex which produces such deviation. However, there are other types of eddies that are not simple vortices. For example, a Rossby wave is an eddy which is an undulation that is a deviation from mean flow, but does not have the local closed streamlines of a vortex.
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