A R, Premlata and Tripathi, M K and Sahu, Kirti Chandra
(2015)
Dynamics of rising bubble inside a viscosity-stratified medium.
Physics of Fluids, 27 (072105).
pp. 1-15.
ISSN 1070-6631
Abstract
The rising bubble dynamics in an unconfined quiescent viscosity-stratified medium
has been numerically investigated. This is frequently encountered in industrial as well
as natural phenomena. In spite of the large number of studies carried out on bubbles
and drops, very few studies have examined the influence of viscosity stratification
on bubble rise dynamics. To the best of our knowledge, none of them have isolated
the e
ff
ects of viscosity-stratification alone, even though it is known to influence the
dynamics extensively, which is the main objective of the present study. By conducting
time-dependent simulations, we present a library of bubble shapes in the Galilei and
the Eötvös numbers plane. Our results demonstrate some counter-intuitive phenom-
ena for certain range of parameters due to the presence of viscosity stratification
in the surrounding fluid. We found that in a linearly increasing viscosity medium,
for certain values of parameters, bubble undergoes large deformation by forming an
elongated skirt, while the skirt tends to physically separate the wake region from the
rest of the surrounding fluid. This peculiar dynamics is attributed to the migration
of less viscous fluid that is carried in the wake of the bubble as it rises, and thereby
creating an increasingly larger viscosity contrast between the fluid occupied in the
wake region and the surrounding fluid, unlike that observed in a constant viscosity
medium. It is also observed that the e
ff
ect of viscosity stratification is qualitatively
di
ff
erent for di
ff
erent regimes of the dimensionless parameters. In future, it will be
interesting to investigate this problem in three-dimensions.
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