Counter rotation in an orbitally shaken glass of beer
Swirling a glass of wine...
It is common knowledge that prescribing an orbital motion to a glass of
wine generates a rotating gravity wave that comes along with a swirling
mean flow. This mean flow rotates in the direction of the wave and
recirculates radially and vertically, thus permanently pushing
new fluid to the surface where it aerates and releases the wine's
Precisely the same kind of orbital shaking is used on a more
professional level in bioreactors for the cultivation of biological cells.
There, the presence of the mean flow prevents sedimentation and ensures
efficient gas exchange, avoiding the damagingly high shear rates that
immersed stirrers would cause.
... or a glass of beer?
Surprisingly, when the liquid is covered by a floating cohesive material, for instance a thin layer of foam in a glass of beer, the mean rotation at the surface can reverse!
This intriguing counter-rotation can also be observed with coffee cream, tea scum, cohesive powder, provided that the wave amplitude is small and the surface covering fraction is large.
We have shown that the mechanism for counter-rotation is a fluid analog of the rolling without slipping motion of a planetary gear train: for sufficiently large density, the covered surface behaves as a rigid raft transported by the rotating sloshing wave, and friction with the near-wall low-velocity fluid produces a negative torque which can overcome the positive Stokes drift rotation induced by the wave.
- Counter-rotation in an orbitally shaken glass of beer
F. Moisy, J. Bouvard, W. Herreman, EPL 122, 34002 (2018)
[Abstract | PDF | Suppl. Material | Suppl. Movies]
- Mean mass transport in an orbitally shaken cylindrical container
J. Bouvard, W. Herreman and F. Moisy, Phys. Rev. Fluids 2, 084801 (2017)
[Abstract | PDF]