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| Thursday, January 4 — Session 3: Hydrodynamics |
| 8:30-9:10 am |
George Haller
Massachusetts Institute of Technology
Email: ghaller@mit.edu
Where do particles go in fluid flows?
In this talk I will survey recent results on the motion of infinitesimally small and finite-size particles in fluid flows. In both cases, the motion is governed by Lagrangian coherent structures that can now be located with high precision even for turbulent flows. I will illustrate the main results on experimental and numerical fluid data sets. |
| 9:10-9:30 am |
Woodrow Shew
National Institute of Health
Email: sheww@mail.nih.gov
authors: Woodrow L. Shew, Yoann Gasteuil, Mattieu Gibert, Bernard Castaing,
Jean-Francois Pinton
Smart particles: Lagrangian measurements of scalars in turbulent flow
Uncountable natural and engineered systems depend on the mixing of scalar quanities such as temperature or concentration by the disorderly motions of turbulent fluids. Predictive modelling as well as fundamental understanding of such systems is often easier within the framework of Lagrangian fluid dynamics; i.e. relevant quantities are measured along fluid trajectories instead of at fixed locations (Eulerian). We present the first experimental laboratory-scale measurement of temperature in a Lagrangian frame. A small neutrally-buoyant capsule containing electronic sensors and wireless communication capabilities measures temperature in turbulent Rayleigh-Benard thermal convection. Temperature fluctuation time series and statistics reveal important differences compared to Eulerian measurements. |
| 9:30-9:50 am |
David Roberts
Los Alamos National Laboratory
Email: dcr@lanl.gov
authors: David C. Roberts* (LANL) and Yves Pomeau (LPS, Ecole Normale
Superieure)
When superfluids are a drag
It is widely accepted that a superfluid flow exhibits a critical velocity below which there is no dissipation. However, often-neglected zero-temperature quantum fluctuations have implications for the existence of this critical velocity. The drag force on an object created by the scattering of these quantum fluctuations in a three-dimensional, weakly interacting Bose-Einstein condensate will be discussed. A non-zero force at low velocities is found to exist, which suggests that the effective critical velocity in these systems is zero. Some of the implications of these results will be considered. |
| 9:50-10:30 am |
Anne Juel
University of Manchester
Email: anne.juel@manchester.ac.uk
authors: Shreyas Jalikop and Emma Talib, School of Mathematics, University of Manchester, UKselect:
The influence of viscosity on the frozen wave instability
Horizontally vibrated interfaces exhibit a rich variety of interesting dynamics which have been surprisingly neglected to date. The `frozen wave' instability (FW) is characterised by the formation of a standing wave pattern when a vessel containing stably stratified layers of immiscible liquids is oscillated horizontally, above a critical value of the acceleration. We investigate the onset of instability using the powerful combination of experiments and
linear stability theory, and achieve quantitative agreement between the two despite a simplified model geometry. We focus on viscosity ratios $1 \le N_1=\nu_2/\nu_1 \le 6 \times 10^4$ (where $\nu_1$ and $\nu_2$ denote the kinematic viscosities of the lower and upper layers respectively), and find that increasing $N_1$ (by increasing the upper layer viscosity $\nu_2$) leads, surprisingly, to the destabilisation of the interface over a wide range of viscosity contrasts. In fact we identify four regions of $N_1$ where qualitatively different dynamics occur, which are reflected in the non-monotonic dependences of the most unstable wavenumber and critical amplitude on $N_1$. This intricate dependence of the instability is due to considerable changes in the time-averaged perturbation vorticity distribution near the
interface. Finally, perspectives are given on the influence of viscosity contrast on the nonlinear growth of the FW. |
| 11-11:40 am |
L. Mahadevan
Harvard University, Engineering and Applied Sciences, Organismic and Evolutionary Biology, and Systems Biology
Extreme elastohydrodynamics: of flags, flying carpets and flytraps
The borderlands between elasticity and hydrodynamics lead naturally to a number of moving boundary problems in elastohydrodynamics. I will discuss some phenomena in this rich area involving extreme geometries: the flutter of a slender flag in a breeze (and the connection to fish swimming), the lift on a sheet sliding near a wall (and the connection to the mythical flying carpet), and the dynamics of fluid-filled tissues (and the connection to rapid movements in some plants and fungi).
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