Buoyant mixing
 french version
The buoyant mixing of two fluids of different densities is a widespread phenomenon
in natural sytems (oceanography, hydrology,atmospheric sciences) with large
potential consequences on the environment. It is also encountered frequently in
chemical or petroleum engineering.
We study the buoyant mixing of two fluids of different densities initally separted
in an unstable configuration (the heavier fluid is above the lighter fluid) in a
confined geometry of a tilted tube (the angle is fixed for each experiment).
The flow results from a competition between:
- Fluids interpenetration due to the longitudinal gravity component.
- Transverse mixing due to Kelvin-Helmholtz instabilites at the
interface.
- Segregation of the fluids due to the transverse gravity component.
The flow displays a variety of regime depending on the two control parameters, the tube
angle and density difference. For a tube close to vertical and for a large density
contrast, the flow is turbulent and a strong transverse mixing is observed.
In contrast, for a nearly horizontal tube and a small density contrast, there is a
laminar counterflow without mixing. Between these two extreme cases, the flow is
laminar with intermittent turbulent bursts.
(video)
The velocity field (obtained by particle image velocimetry, PIV) and
the concentration field (obtained by laser induced fluorescence, LIF)
give us a local view. These fields allow us to model the turbulent flow by a
Reynolds stress-mixing length model. The laminar counterflow is modelised by quasi parallel
flow.
This research is pursude in cooperation with the
Toulouse Institute of fluid mechanics (Y. Hallez and J.
Magnaudet) and
The Physics Department of ENS Lyon (J.-C. Tisserand, F. Chilla
and B. Castaing)
and in the framework of an ANR program.
Publications
- Laser induced fluorescence measurements of buoyancy driven
mixing in tilted tubes
T. Séon, , E. J. Hinch,B. Perrin, D. Salin, and J. P. Hulin, Phys.
Fluids , 18, 041701 (2006)
- Front dynamics and macroscopic diffusion in buoyant mixing in a
tilted tube
T. Séon, J. Znaien, E. J. Hinch,B. Perrin, D. Salin, and J. P. Hulin,
Phys. Fluids, 19, 125105 (2007)
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