Orbital sloshing in a glass of beer

The orbital shaking motion of a cylindrical container is very useful in biology, for instance to ensure a good oxygenation in cell cultures. But it can also be playful when the cylinder turns out to be a glass full of wine or beer.

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The sloshing wave generated by the orbital motion comes along a swirling mean flow. With Frédéric Moisy and Wietze Herreman (FAST, Paris-Saclay), we quantified this mean flow caused by Stokes drift,  both experimentally and analytically. It is rotating in the same direction as the forcing, with some small differences with viscosity.

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What was really surprising is the effect of adding particles or foam on the surface: the rotation of the mean flow can change in the other way! You can easily observe this phenomenon by yourself at home or at your local pub...