Eddy

From Wacklepedia - The Free Encyclopedia

In fluid dynamics, an eddy is the swirling of water and the reverse current created when water flows past an obstacle. The moving water creates a space devoid of downstream-flowing water on the downstream side of the object. Water behind the obstacle flows into the void creating a swirl of water on each edge of the obstacle, followed by a short reverse flow of water behind the obstacle flowing upstream, toward the back of the obstacle. This phenomenon is most visible behind large emergent rocks in swift-flowing rivers.