Fluid Dynamics/ITS Seminar: Evan Variano, University of California at Berkeley

(this is a regularly-scheduled Institute for Theoretical Science seminar)

Title: Turbulent transport of non-spherical suspended particles: particle shape, size and rotation

Date: Tuesday, April 26, 2016

Time: 4 pm to 5 pm
Location: ITS Conference Room, 472 Willamette Hall

Evan Variano is an associate professor at UC Berkeley in the Department of Civil and Environmental Engineering. His research interests span transport and mixing in flows inspired by environmental processes, often at the intersection of Ecology and Fluid dynamics.

Abstract:

Natural particles suspended in water are often non-spherical. We explore the ways in which particle size and shape affects particle motion, focusing on particle parameters relevant for plankton, sediment aggregates, or autonomous vehicles.  We find that shape has only a very weak effect on particle angular velocity, which is a quantity calculated with respect the global reference frame (i.e. east/north/up). If we analyze rotation in a particle’s local frame (i.e. the particle’s principle axes of rotation), then particle shape has a strong effect on rotation. In the local frame, rotation is described by two components: tumbling and spinning. We find that rod-shaped particles spin more than they tumble, and we find that disc-shaped particles tumble more than they spin. These preferential rotations, as well as total angular velocity, decrease with increasing particle size.  Such behavior is indicative of how particles respond to the directional influence of vortex tubes in turbulence, and such response has implications for particle motion other than rotation. Understanding particle alignment is relevant for predicting particle-particle collision rates, particle-wall collision rates, and the shear-driven breakup of aggregates. We discuss these briefly in the context of what can be concluded from the rotation data discussed above.

More information: Evan’s website.

Please email Leif Karlstrom if you would like to schedule a meeting with Evan during his visit.

abstract_Variano_2016(1)

Fluid Dynamics/ITS Seminar: Josef Dufek, Geogia Institute of Technology

Title: The fluid dynamics of explosive volcanic eruptions: Multiscale flow in eruptive plumes and pyroclastic density currents

Date: Wednesday, April 13, 2016

Time: 1 pm to 2 pm
Location: ITS Conference Room, 472 Willamette Hall

Josef Dufek is an associate professor at Georgia Tech in the School of and Planetary Sciences. He is a Blanchard-Miliken Fellow and recipient of the American Geophysical Union Macelwane Medal in 2012.  He has wide-ranging fluids interests that span basic multiphase granular flows, numerical methods for multiphase turbulent flow, and analog laboratory experiments.

Abstract:

Explosive volcanic eruptions produce flows that span a range of fluid dynamic regimes, and the ability of these flows to transform from one regime to another plays a significant role in their ability to modify the crust, landscape and atmosphere and produce hazardous conditions. A growing body of numerical, experimental and observational evidence indicates that homogeneity in particle-fluid systems is the exception rather than the rule. Particle segregation is not a passive process, and can feedback in the rheology of granular mixtures controlling the mixing and run-out distance of particle-laden flows. The aim of this talk is to discuss progress in using fluid and granular mechanics to understand the multiphase transport physics of volcanic flows, and demonstrate how an understanding of the dynamics of these high-energy, end member flows yields insight into a range of other geophysical flow types.

I will discuss the use of multiphase models in addressing the different scales of fluid motion in volcanic multiphase flow as well as how they can provide a platform to integrate microphysical, analogue experiments and observational constraints. Microphysical experiments can provide the necessary closure for statistical mechanics based models, and provide a way to examine grain-scale processes in a probabilistic manner. Such small-scale processes can dramatically alter the flow dynamics. One of the primary goals and utilities of this combined approach is that it enables comparison with diverse datasets, integrating previously disparate observations. In this talk I will illustrate eruptive flow styles that cover very different dynamic ranges and observation types, and in particular discuss the fluid dynamics of near vent entrainment and pyroclastic density currents. In each case, laboratory experiments, numerical modeling results and observations will be combined to decipher physical processes. The insight from these approaches will also be discussed in the context of future terrestrial measurements as well as to give insight into planetary processes where conditions may have differed considerably from those on contemporary Earth.

More information: Joe’s website.

Hope to see you there!

Dufek Seminar Flyer 4.13.16