Ekman layer

In standard boundary-layer theory, the effects of viscous diffusion are usually balanced by convective inertia. When a fluid rotates, however, the dominant balance may instead be struck between diffusion effects and the Coriolis force. Under these circumstances we are dealing with an Ekman layer. In addition to enforcing the zero velocity condition at the wall, these Ekman layers can also control long-range properties of the flow. A classical illustration is given by the everyday experience of how a cup of tea returns to rest after stirring. We might model this from the decay of the rigid body motion through dissipative effects, which reach out from the stationary sides of the cup over a diffusion timescale
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