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Accueil > Actualités > Séminaires > Séminaires 2011

Jeudi 24 mars 2011 à 14h, salle A103 LEGI.

Emmanuella BOUCHE, post-doctorante à l’IMFT.

Titre/Title :
Interactions hydrodynamiques dans un essaim de bulles confinées à grand nombre de Reynolds.

Contact :
Jean-Philippe Matas

Résumé/Abstract :
Bubbles rising in a liquid generate an agitation that is commonly used to improve mixing and transfers. At large Reynolds numbers, unstable wakes develop behind bubbles and cause fluctuations even for a single rising bubble. The overall agitation of the two-phase mixture results from both the fluctuations generated around individual bubbles and hydrodynamic interactions between them. We focus here on two-dimensional bubbles of 4 mm diameter rising within the 1-mm gap of a Hele-Shaw cell filled with water. A previous study characterized the single confined bubble : the motion of both the bubble and the liquid in its vicinity were similar to that of a bubble in an unbounded domain whereas the flow disturbance decays faster, in particular in the wake due to the shear stress at the walls.
We investigate here the agitation generated in a homogeneous swarm at Re=450, for gas volume fractions a from 0.01 and 0.13. The motions and shapes of the bubbles are characterized by high-speed imaging, and velocity fields in the liquid phase are inferred by PIV. New experimental results allow to shed light on the physical mechanisms of bubble-induced agitation in the liquid and on the velocity fluctuations of the bubbles. Preliminary results on the auto-dispersion of the bubbles in the swarm, and on the efficiency of the mixing of a passive scalar will be illustrated.