Computations in Science Seminars
Feb 2019
20
Wed 12:15
Greg Voth, Wesleyan University
e-mail:
Host: William Irvine ()
Organizer: Steven Strong ()
A new view of the dynamics of turbulence from measurements of rotations of particles with complex shapes

Non-spherical particles in turbulent flows are important in a wide range of problems including ice crystals in clouds, fibers in paper-making, marine plankton, and additives for turbulent drag reduction. We have developed experimental methods for precise tracking of the position and orientation of non-spherical particles in intense 3D turbulence. Using 3D printed particles, we can fabricate a wide range of shapes and explore how particle orientation and rotation are affected by particle shape. We find particles are strongly aligned by the turbulence. A simple picture in which particles are aligned by the fluid stretching they experience explains many of the key observations about how particles align and rotate. This same picture sheds new light on some old problems about how vorticity aligns with the strain rate tensor in turbulent flows. It has also allowed us to create a fascinating particle shape which we call a chiral dipole that shows a preferential rotation direction in isotropic turbulent flow.

Feb 2019
27
Wed 12:15
Xiang Cheng, University of Minnesota
e-mail:
Host: Tom Witten ()
Organizer: Grayson Jackson ()
From Flocking Birds to Swarming Bacteria: A Study of the Dynamics of Active Fluids

Active fluids are a novel class of non-equilibrium complex fluids with examples across a wide range of biological and physical systems such as flocking animals, swarming microorganisms, vibrated granular rods, and suspensions of synthetic colloidal swimmers. Different from familiar non-equilibrium systems where free energy is injected from boundaries, an active fluid is a dispersion of large numbers of self-propelled units, which convert the ambient/internal free energy and maintain non-equilibrium steady states at microscopic scales. Due to this distinct feature, active fluids exhibit fascinating and unusual behaviors unseen in conventional complex fluids. Here, combining high-speed confocal microscopy, holographic imaging, rheological measurements and biochemical engineering, we experimentally investigate the dynamics of active fluids. In particular, we use E. coli suspensions as our model system and illustrate three unique properties of active fluids, i.e., (i) abnormal rheology, (ii) enhanced diffusion of passive tracers and (iii) emergence of collective swarming. Using theoretical tools of fluid mechanics and statistical mechanics, we develop a quantitative understanding of these interesting behaviors. Our study illustrates the general organizing principles of active fluids that can be exploited for designing “smart” fluids with controllable fluid properties. Our results also shed new light on fundamental transport processes in microbiological systems.

Mar 2019
13
Wed 12:15
OPEN
Mar 2019
20
Wed 12:15
Hana El-Samad, University of California, San Francisco
e-mail:
Host: Arvind Murugan ()
Organizer: Elizabeth Lee ()
Mar 2019
27
Wed 12:15
Arvind Murugan, University of Chicago
e-mail:
Host: William Irvine ()
Organizer: Peter Chung ()
Apr 2019
3
Wed 12:15
Greg Bewley, Cornell University
e-mail:
Host: William Irvine ()
Apr 2019
10
Wed 12:15
Oskar Hallatschek, UC Berkeley
e-mail:
Host: Arvind Murugan ()
Apr 2019
17
Wed 12:15
Nikta Fakhri, MIT
e-mail:
Apr 2019
24
Wed 12:15
Detlef Lohse, University of Twente
e-mail:
Host: William Irvine ()
May 2019
1
Wed 12:15
Pankaj Mehta, Boston University
e-mail:
Host: Stefano Allesina ()
May 2019
8
Wed 12:15
Thierry Emonet, Yale University
e-mail:
Host: Stephanie Palmer ()
May 2019
15
Wed 12:15
David Lentik, Stanford
e-mail:
Host: William Irvine ()
May 2019
22
Wed 12:15
Joshua Shaevitz, Princeton University
e-mail:
Host: Arvind Murugan ()
May 2019
29
Wed 12:15
Xiaoming Mao, University of Michigan
e-mail:
Host: William Irvine () and Vincenzo Vitelli ()