Experiments in Fluids 26 (1999) 233—239 Springer-Verlag 1999
Bubble capture and migration in Couette—Taylor flow
H. Dje´ ridi, J-F. Fave´ , J-Y. Billard, D. H. Fruman
Bubble capture and migration under the effect of
organized structures in weak turbulent Couette—Taylor ﬂow
between two concentric cylinders, the inner one rotating, has
been investigated. Bubbles generated at the free surface for
large enough angular velocities are sucked into the ﬂow by the
upper organized structures. Then they migrate progressively
from top to bottom by jumping from cell to cell. With an upper
solid stationary wall instead of the free surface, injected
bubbles are trapped by the coherent vortices beyond a critical
Taylor number. However, in this situation there is no migra-
tion mechanism carrying the bubbles from top to bottom. This
particular migration and capture process, able to act against
the forces of buoyancy, has been investigated by perturbing the
ﬂow by adding a vertical plate protruding from the inner
surface of the solid stationary wall. The perturbation so
introduced causes the deformation of the upper coherent
structures and reinstalls the migration of the bubbles.
In a two phase ﬂow the Taylor instabilities, known to exist in
a single phase situation, may have a profound impact on the
capture, break-up and migration of the bubbles constituting
the dispersed phase. Inversely, the presence of the dispersed
phase may modify the ﬂow regimes existing in single phase.
Several experimental investigations have been conducted on
two-phase ﬂows in concentric annulus with a rotating inner
cylinder. One of them concerns the introduction, for visualiz-
ation purposes, of micron size solid particles in small concen-
trations (Dominguez-Lerma et al. 1985), and, in this case, the
single phase ﬂow is indeed unaltered by the presence of the
solid particles. Salhi et al. (1992) investigated the pressure drop
H. Dje´ ridi, J-F. Fave´ , J-Y. Billard
Laboratoire d’Hydrodynamique, Ecole Navale, Lanve´ oc Poulmic,
F-29240 Brest Naval, France
D. H. Fruman
Groupe Phe´ nome` nes d’Interface, ENSTA,
F-91120 Palaiseau, France
Correspondence to: H. Dje´ ridi
This work is supported by French Navy. The authors also gratefully
acknowledge valuable discussions about that work with J. Berthelot.
We are grateful to E. Rindel for his technical assistance.
in a gas—liquid Couette—Poiseuille ﬂow but were not interested
neither by the bubble capture in the Taylor cells nor by their
impact on the ﬂow structure. On the contrary, Shiomi et al.
(1993) investigated the behavior of the gas—liquid bubbly ﬂow
in a concentric annulus with axial ﬂow, for Taylor numbers
larger than 107, corresponding to the turbulent regime.
A gas—liquid mixture is injected at the bottom of the apparatus
and the volumetric ﬂuxes of both gas and liquid were
measured. They focused their interest on the correlation of the
ﬂow pattern with the volumetric ﬂuxes and the rotational speed
of the inner cylinder and described three main patterns:
dispersed bubbly, ring form and spiral ﬂow. However, they did
not investigate the effects of the gas—liquid bubbly mixture on
the behavior of the vortices present in the turbulent ﬂow. In
our case, we are interested in the determination of the mutual
effects between the dispersed phase and the ﬂow structure for
low Taylor numbers corresponding to the ﬁrst instabilities.
This investigation is thus very much different but complement-
ary of the previous ones.
It is now well documented that the purely azimuthal ﬂow in
a circular Couette apparatus will develop a Taylor Vortex Flow
(TVF) situation, beyond a speciﬁc Reynolds number, where
superposed counter rotating cells, with a height theoretically
equal to the gap, will appear in the entire length of the
apparatus (Taylor 1923). Those cells, independent from the
angular position, are known as the ﬁrst Taylor instability.
When the angular velocity is increased, a second instability
occurs (Andereck et al. 1986), corresponding to the Wavy
Vortex ﬂow (WVF) regime and characterized by the super-
position of an azimuthal wave on the initial cells.
Because of the rotating ﬂow prevailing in the cells it can be
hypothesized that centrifugal effects will eject any foreign
material, solid or gas, towards the outer or inner part of the
cells respectively. However, the capture process will be more or
less altered by the effect of gravity, which will tend to sediment
the solid particles or separate the gas bubbles. Therefore,
depending on the attitude of the axis of rotation of the Couette
apparatus relative to the direction of gravity, the whole process
can be quite different.
In order to conduct a preliminary investigation of the bubble
motion in this complex ﬂow situation, tests were conducted in
a vertical Couette—Taylor apparatus having a rotating inner
cylinder and a static outer cylinder. Three conditions for the
upper liquid boundary in the gap were tested: an upper free
surface, and a ﬂat solid wall with or without a removable
vertical plate. In the ﬁrst case, the ventilated ﬂow was obtained
naturally for a sufﬁcient rotational velocity of the inner
cylinder. Bubbles were generated by inverted breaking waves