What is an eddy in fluid dynamics?

An eddy is the swirling of a fluid and the reverse current created when a fluid is in a turbulent flow regime. When a moving fluid encounters an obstacle, it creates a void of downstream-flowing fluid, causing fluid to swirl on each edge and flow backward upstream toward the obstacle. While vortices are simple examples of eddies, other types like Rossby waves exist without local closed streamlines.

What we know

• An eddy is defined as the swirling of a fluid and the reverse current created during turbulent flow. [1, 2]
• Moving fluid past an obstacle creates a void on the downstream side, leading to fluid swirls on each edge and a short reverse flow upstream. [2]
• Eddies can be naturally observed behind large emergent rocks in swift-flowing rivers. [2]
• Not all eddies are simple vortices; a Rossby wave is an eddy that deviates from mean flow without local closed streamlines. [2]

Where to go next

• how it workedHow do vortices behave within fluid motion?
• a case in pointWhat are Rossby waves in geophysical flows?
• the bigger pictureWhat is fluid dynamics?
• how we knowHow do obstacles in rivers create observable turbulence?
• compared withHow do electromagnetic eddy currents compare to fluid eddies?
• an unexpected connectionHow do magnetic fields produce eddy current brakes?Although fluid eddies involve swirling liquids and gases, the concept of an eddy extends into electromagnetism to describe loops of electric current induced by changing magnetic fields that can stop moving objects.

Sources

• [1]eddy (Wikidata Q994122) · CC0 1.0
• [2]Eddy (fluid dynamics) · CC BY-SA 4.0
• [3]Eddy · CC BY-SA 4.0
• [4]Outline of fluid dynamics · CC BY-SA 4.0
• [5]Computational fluid dynamics · CC BY-SA 4.0