1:00–2:00 pm
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THE ONSET AND GROWTH OF VISCOUS FINGERING FOR DIFFERENT FLUIDS IN RADIAL AND LINEAR GEOMETRIES
Dynamic instabilities drive pattern formation throughout natural systems, from the growth of snowflakes, to the formation of river networks. The viscous fingering instability is a classic example of branching growth and has been used to study pattern formation for over half a century. This instability occurs when a low viscosity fluid displaces one of higher viscosity in a confined geometry, such as in a Hele-Shaw cell, a thin gap between a pair of glass plates. When immiscible fluids are used, surface tension between the fluids is a stabilizing force that controls the characteristic length scale of the patterns and prevents small scale structure across the width of the gap. In the miscible limit, where surface tension is absent, the system develops additional structure across the small gap between the plates; this structure plays an important role in subsequent pattern formation in both radial and linear geometries.
In this talk, I will show experiments investigating how the creation of this structure affects the onset of when viscous fingering first appears. I also explore two ways that the structure can be perturbed in order to change the characteristics of the pattern: by allowing sufficient time for diffusion to blur the interface, I can drive the system into a new type of fingering. By actively applying shear to the system, so that the structure becomes tilted within the cell, I can delay finger formation.
An important feature of the structure that forms in miscible systems in a Hele-Shaw cell, is that the fluids become stratified into three layers so that there is always a heavier fluid residing above a lighter one. Because of this, another instability, known as the Rayleigh-Taylor instability, occurs as the heavier fluid settles to the bottom of the cell. This geometry provides a novel test bed for this classical instability but with the added importance of confinement that can suppress the instability entirely.
Committee members:
Sidney Nagel (chair)
Heinrich Jaeger
Arvind Murugan
David Schmitz
Thomas is currently seeking postdoctoral positions in the field of soft matter physics.