Event
Leaders in Mechanical Engineering Lecture Series
Friday, March 16, 2007
2:00 p.m.
1110 Jeong Kim Engineering Building
James Barrett
301 405 2097
jcb@umd.edu
Jerry Gollub - Haverford College/University of Pennsylvania
Origins of Irreversibility in Fluid Dynamics: Chaotic Particle Interactions and Chaotic Mixing
Abstract: Although much of the microscopic world is governed by time-reversible equations of motion, the macroscopic world is Irreversible. Precisely how does this happen in fluid dynamics? To elucidate it, we can consider the slow flow of a Newtonian fluid at very low Reynolds number, which is known to be reversible. Now consider fluids containing solid particles that are too large to exhibit Brownian motion, i.e. suspensions. The accepted wisdom is that they are also governed by reversible equations, but we have shown experimentally that the particles in a sheared suspension do not return to their starting positions if the fluid sheared beyond a certain threshold. Instead they appear to undergo a random walk after one or more cycles. I will compare the experiments with numerical simulations demonstrating that the particles interact chaotically with each other, and that the strength of the chaos grows dramatically above the threshold for irreversibility. The comparison illuminates the connections between chaos, reversibility, and predictability.[1]
Finally, I will give a second example showing how irreversibility is responsible for the mixing or inter-penetration of two stirred fluids.
[1] This work was done jointly with D.J. Pine, J. Brady, and A. Leshansky.
Biography: Jerry Gollub is Professor of Physics (and also the John and Barbara Bush Professor in the Natural Sciences) at Haverford Colege. His research is in the general area of Nonlinear Physics, which is concerned with the mesoscopic and macroscopic behavior of complex systems. Often these systems are described by nonlinear partial differential equations such as the Navier-Stokes equations of fluid motion. His group has conducted experimental work on the following topics over the years: hydrodynamic instabilities and the transition to chaos and turbulence in fluids; the morphology of growing crystals; the dynamics of nonlinear waves, turbulent convection induced by thermal gradients; thin film flows; and spatiotemporal chaos. Current projects include the dynamics of granular materials, which show many interesting nonlinear phenomena, problems related to mixing in fluids, and experiments involving microfluidic flows. Many Haverford students, postdoctoral associates, and visitors have participated in these projects.
Jerry Gollub was elected to membership in the National Academy of Sciences in 1993, and became a Fellow of the American Academy of Arts and Sciences in 1992. He was awarded the Fluid Dynamics Prize of the American Physical Society in 2003, and was the first recipient of the APS Award for Research in an Undergraduate Institution in 1985. He was a Guggenheim Fellow in 1984-85, won an international "Science for Art" Award in 1994, and earlier held Danforth and Woodrow Wilson Fellowships.
Gollub was a Morris Loeb Lecturer in Physics at Harvard University in 1990, a Sigma Xi National Lecturer in 1983-85, and a Visiting Professor at Ecole Normale in 1985, and 1991. He previously served as Provost (Chief Academic Officer) at Haverford. Gollu received his Ph.D. in experimental condensed matter physics at Harvard University in 1971.
