Speaker: Julien R. Landel (Cambridge)
Title: Transport and dispersion in quasi-two-dimensional turbulent jets, and the convective mass transfer of a viscous drop in a thin film.
Abstract: First, I will present some experimental and theoretical results about the transport and dispersion properties of quasi-two-dimensional jets. This study is relevant to rivers flowing into lakes or oceans. In the event of a spillage of pollutants into a river, it is critical to understand how these agents disperse with the flow in order to assess damage to the environment. For such flows, characteristic streamwise and cross-stream dimensions can be much larger than the fluid-layer thickness, and so the flow develops in a confined or quasi-two-dimensional environment. From experimental observations using dyed jets and PIV, we find that the structure of a quasi-two-dimensional jet consists of a high-speed meandering core with large counter-rotating eddies developing on alternate sides of the core. To understand the transport and dispersion properties of quasi-two-dimensional jets we solve a time-dependent advection-diffusion equation. Our analytical solution is supported by experimental and numerical releases of tracers in jets. We find that a significant amount of tracers can be transported faster than the advection speed predicted using a top-hat velocity profile in the jet. We discuss the implications for pollution control in river flows.
In the second part of my talk, I will show some recent experimental and theoretical results about the fluid mechanics of cleaning a viscous drop attached to an inclined planar surface using a thin gravity-driven film. The drop cannot be detached from the surface by mechanical forces, but instead dissolves slowly into the film. This cleaning problem is very common in the food industry, as well as in our daily life with household dishwashers. My collaborators and I have developed a model for the convective mass transfer of the drop fluid into the film. The overall mass flux is modelled using an analogy with Newton’s law of cooling. A common way to model the mass transfer coefficient, or Sherwood number, is by solving the advection-diffusion equation above the drop-film interface. We find that the concentration in the drop decreases exponentially in time and the Sherwood number is a function of the Péclet number. I will then compare our theoretical predictions with experimental results. Using the dye attenuation technique, we measured the flux of tracers out of the drop as the film flows over it. We analyzed the impact of the drop size, the film Péclet number and other parameters on the dissolution of the drop fluid. Our experimental results are in good agreement with the Newton cooling model. On the other hand, the dependence of the Sherwood number with the Péclet number does not agree perfectly with the theoretical predictions. This raises questions about some of the common hypotheses used to model this problem. In particular, I will discuss whether the impact of the drop onto the film flow can be neglected, as well as the influence of the mass transport inside the drop.
Bjørn Kjos-Hanssen will briefly present his COCOA conference paper.
Prof. David Ross will speak briefly on finite game theory..
On Friday December 12th, Loren Acton and Jennifer Trosper will present a special colloquium.
L. Acton: 1:00pm – 1:45pm
J. Trosper: 2:00pm – 2:45pm
You are all invited to join. Titles and abstracts will follow, as well as location.
Loren W. Acton, P.hD. in solar physics. Dr. Acton flew on Space Shuttle mission STS-51-F in 1985, after seven years of training, as a payload specialist. During his mission, he orbited the Earth about 126 times. Dr. Acton is currently a research Professor in the Solar Physics Group at Montana State University.
Jennifer Trosper. Mars Curiosity Mission Manager and more recently Mars Curiosity Deputy Project Manager. Responsible for leading the Curiosity operational mission. 2013 named JPL Fellow in Mars rover surface operations, 2013 NASA Exceptional Achievement Medal for Curiosity operations work, 2013 “Breaking the glass Ceiling” California Legislature award recipient.
Robert Bates will defend his doctoral dissertation.
Yuri Gurevich will visit 16-22 December.
We scheduled his talk for Dec 18 at 3-4PM in POST 302.
The graduation ceremony is at 4:30PM, and after that we will go for a dinner. The talk will not be on the topic of Yuri’s new interest: privacy. The abstract is below.
Please email Dusko Pavlovic by Friday Noon if you want to join us for dinner.
TITLE: Inverse Privacy
SPEAKER: Yuri Gurevich, Microsoft Research
ABSTRACT: We say that an item of your personal information is directly private if you
have it but nobody else does, and it is inversely private if somebody has
it but you do not. We analyze the provenance of inverse privacy and its ascent to dominance (by volume and value) over direct privacy, and we argue that — and how — inverse privacy can be reduced to more reasonable levels.
This is joint work with our Microsoft colleagues Efim Hudis and Jeannette Wing.
DRAFT PAPER ON:
http://research.microsoft.com/en-us/um/people/gurevich/annotated.htm