2a. Plane Couette flow, from experimental to idealized conditions

The next two animations show a flow close to experimental conditions. You will see that the flow exhibits unstable but recurrent structures. This is the physics we need to explain: how do we identify these structures? And how are they related?

The plane Couette walls are in principle infinite, but the size of structures you will observe is comparable to the wall-wall separation. Hence rather small aspect ratio cells (spanwise, streamwise cell size measured in wall-to-wall distance units) can capture the essential physics. The third animation shows a qualitatively similar flow whose dynamics are simpler to analyze then the first two.

In all simulations presented here the Reynolds number is 400, chosen so that the wall-wall separation fits approximately the diameter of the numerically (and experimentally) observed unsteady streamwise rolls.