Dr. Jeffrey Morris Halliburton Energy Services,
"Fluid Mechanics of Suspensions:
From Rheology to Pattern Formation
Suspensions of solid particles in Newtonian liquids play a special role in the study of mixture flow. This class of materials exhibits a number of the features of other complex fluids, particularly non-Newtonian rheology and nonlinear dynamical system behavior, in a relatively simple system where particle effects are readily isolated. As a result, an abundance of study over the last three decades and more has produced a substantial body of understanding of suspensions, leading to the promise of a true fluid dynamics for these mixtures. Focusing attention to suspensions of essentially monodisperse near-hard spheres, several fluid mechanical topics – specifically rheology, bulk migration, and free-surface effects – are addressed. These demonstrate the strong influence of microscale details upon macroscopic flow behavior, the rich behavior of suspensions, and the need for better understanding of boundary conditions.
We first consider the rheology of the mixture. Here particular attention is paid to the role of flow-induced microstructure characterized by the pair correlation, determined in our work from sampling of flows simulated by Stokesian Dynamics, in establishing the bulk stress. At the bulk scale the normal stress rheology is shown to profoundly impact the flow behavior of suspensions by driving migration of the particles to yield highly nonuniform particle fraction. This is illustrated by consideration of shear-induced migration in a number of flows of noncolloidal as well as Brownian suspensions, using a model which captures the migration based upon the normal stress contribution of the solid particles.
The model is shown to be applicable to more complex materials in fully-bounded flows through its accurate prediction of pattern formation to columns and stripes of the particle phase in, respectively, static and sheared electrorheological fluids; these are suspensions of polarizable particles which align under the influence of an applied electric field. These successful applications are contrasted with the pattern formation in free surface flow of suspension in a partially-filled Couette geometry, in which shear-induced demixing causes the formation concentrated bands; this is a phenomenon for which a successful model has not been clearly demonstrated. In this flow, the bands are found to exhibit dynamics with potential for chaotic motion, quite similar to dynamics described by the Kuramoto-Sivashinsky equation. Our experiments in this and other free surface flows of suspensions show the free surface plays a pronounced but poorly understood role in the mixture dynamics.
BRIEF ACADEMIC/EMPLOYMENT HISTORY:
BChE, Georgia Tech, chemical engineering, 1989.
PhD, Cal Tech, chemical engineering, 1995. Suspensions: microstructure, diffusion, and inhomogeneous flow.
Postdoctoral fellow, Royal Dutch Shell BV, 1994-95.
Assistant Professor of Chemical Engineering, Georgia Tech, 1995 - 2002.
Visiting Professor, U. Marseille Lab. IUSTI since 1999.
Halliburton since 2002, currently Principal Scientist.