Philip G. Saffman
     Memorial Symposium

May 29, 2009 · Pasadena, CA

Philip Saffman and Viscous Flow Theory
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(Lees-Kubota Lecture Hall)
Howard Stone

Philip Saffman made valuable theoretical contributions to different areas of low-Reynolds-number hydrodynamics. Three themes are selected for this brief survey: (i) the lift force on a sphere in a shear flow at small, but finite Reynolds number, (ii) Brownian motion in thin liquid films, and (iii) particle motion in rapidly rotating flows. In addition, brief descriptions are given of some of Saffman's other contributions including dispersion in porous media, the average velocity of sedimenting suspensions, and compressible low-Reynolds-number flows.

A New Calculus for Two Dimensional Vortex Dynamics
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(Lees-Kubota Lecture Hall)
Darren Crowdy

In classical fluid dynamics, an important problem arising in a variety of applications is to understand how vorticity interacts with solid objects (e.g. aerofoils, obstacles or stirrers). For planar flows, a variety of powerful mathematical results exist (complex variable methods, conformal mapping, Kirchhoff-Routh theory) that have been used to study such problems but the constructions are usually restricted to problems with just one, or perhaps two, objects. Expressed another way, most studies deal only with fluid regions that are simply or doubly connected. There has been a general and longstanding perception that problems involving fluid regions of higher connectivity are too challenging to be tackled analytically.

The talk will show that there is a way to formulate the theory so that the relevant fluid dynamical formulae are exactly the same irrespective of the connectivity of the domain. This provides a flexible and unified tool for modelling the fluid dynamical interaction of multiple objects/aerofoils/obstacles/stirrers in ideal flow and their interaction with free vortices.

Nonlinear Cascades: Short Scales, and Possibly Turbulence, Without Noise
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(Lees-Kubota Lecture Hall)
Stephen Cowley

We will discuss one of the ways by which small scales can sometimes arise from large scales, and whether small scales are "inevitable." In particular, for some example high-Reynolds-number flows we will argue by means of scaling arguments and numerical calculations how, without the presence of noise, short-scales can evolve naturally out of initial conditions once exponentially small terms are accounted for. We will indirectly address the question as to whether it is possible to design a "noise-free" experiment that suppresses turbulence.

Direct Numerical Simulation of Turbulent Flows
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(Lees-Kubota Lecture Hall)
Javier Jiménez

The first direct numerical simulations of turbulent flows date from the 1980s, and were from the beginning responsible for a renaissance in the study of turbulence. Although they are still constrained by computer power, the amount of detail possible has increased enormously in this quarter century, and the flows that can now be studied overlap what has always been considered the experimental range. An overview of some of the accomplishments will be given, including the early identification of coherent vorticity in isotropic turbulence, to which Prof. Saffman was an important contributor, reduced models of wall-bounded flows, and newer evidence on some old experimental problems, such as inner-outer interactions and potential intermittency in turbulent boundary layers.

Philip Saffman: Memories and Legacies
(Lees-Kubota Lecture Hall)
Paul Dimotakis

Some personal impressions of Philip Saffman as teacher and mentor, scientist and colleague, theoretician and experimentalist, and friend.

From Cascades in Turbulence
to Cascades on Complex Networks
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(Lees-Kubota Lecture Hall)
James Gleeson

I will discuss Philip's influence on my research, ranging from stochastic models of turbulence to current interests in cascade dynamics on random networks.

One Dimensional Energy Spectrum
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(Lees-Kubota Lecture Hall)
Tom Lundgren

The one dimensional turbulent energy spectrum is obtained by a matched asymptotic expansion method which essentially closes the Karman-Howarth equation. Simple approximations for the inner and outer second order structure functions are used to construct a composite second order structure function as the product of the inner and outer functions divided by their overlapping common parts (which is the Kolmogorov 2/3 law). One dimensional inner and outer spectra are computed separately from the structure functions and a composite spectrum is constructed as the product of these spectra divided by their common parts (which in this case is the Kolmogorov 5/3 spectral law). Results agree with experiments.

Nonlinear Motion of Atoms Bathed in Light
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(Lees-Kubota Lecture Hall)
Mark Saffman

I will discuss how the interaction of cold atoms with near resonant coherent light leads to novel nonlinear motion including collective focusing of light and atoms, multi-component solitary waves, and instabilities. Highly excited Rydberg atoms can be used to create controllable long range interactions leading to stable higher dimensional solitons.