| dc.description.abstract | The objective of this research is to investigate the interfacial instability of suspensions
in a Hele-Shaw cell, which involves a dynamical coupling between particle transport and
fluid-fluid interfacial deformations. Interfacial instabilities have remained an important
subject of research given their complicated nature. They are commonplace in multiphase
flows such as enhanced oil recovery, lung airways and micro-fluidic droplets, and controlling
them is of critical importance. The inclusion of particles in fluid flows can also
modify the interfacial dynamics, which yet remains not well understood.
The Saffman-Taylor fingering instability occurs when a less viscous fluid displaces a
more viscous one in porous media, which has been extensively studied for decades. The
interface is supposed to be stable in the reverse scenario, in which the more viscous fluid
invades the less viscous one. Surprisingly, the inclusion of particles can fundamentally
change the interfacial dynamics and even lead to interfacial instability in the absence of
the unstable fluid viscosity ratio. This instability phenomenon was first reported by Tang et
al and extended to squeezing suspension flows by Ramachandran. However, the research
on this topic has remained qualitative.
In this research, we carry out rigorous experiments to characterize the fingering instability
introduced particles, by varying the particle volume fraction and the gap thickness
over particle diameter ratio h=D. The experimental data are analyzed utilizing advanced
image processing techniques to aid our understanding of the phenomenon. Theoretically,
we use the suspension balance model to validate the shear-induced migration upstream
of the expanding interface and successfully explain the mechanism behind fingering. The
project is then extended to bi-disperse suspensions. The experiments are conducted with
particles having different diameters by varying both the bulk particle concentration and
the respective concentration of each particle species. We observe similar fingering patterns
and find that the addition of small amount of large particles leads to an earlier onset
of fingering. The suspension balance model is modified to accommodate the bi-disperse
suspension system and then utilized to quantitatively explore the dynamics. | en |
