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MEchanics GAthering -MEGA- Seminar: The Latest from LFMI - Fluid Mechanics and Instabilities

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Event details

Date and time 04.10.2018 16:1517:30  
Place and room
Speaker Mathias Bechert, EPFL STI IGM Laboratory of Fluid Mechanics and Instabilities (LFMI)Gaëtan Lerisson, EPFL STI IGM Laboratory of Fluid Mechanics and Instabilities (LFMI)
Category Conferences - Seminars
Talk 1: Transport of fibers in confined micro-channels by Mathias Bechert
Abstract The behavior of fibers transported by a flow in confined geometries is important for many applications, e.g., paper production, hydraulic fracturing, or biomedical technologies. The complex interactions between the fiber and the surrounding flow lead to various dynamical behavior, e.g. oscillatory movement between the channel walls or rotation of the fiber. In this talk I will present a method using an approximative model of reduced dimensionality to efficiently explore these dynamics with respect to practically relevant control parameters, e.g., channel size or fiber properties. In particular, we will have a look at the similarities and differences between symmetric, asymmetric and flexible fibers. Apart from helping to improve industrial and biomedical processes, the new insights also open ways to develop flow sensors.

Talk 2: Destabilization of a viscous liquid film below an inclined flat substrate by Gaëtan Lerisson
Abstract Falling liquid film on a substrate have been extensively studied. While numerous studies are dedicated to the case where the gravity acts as a stabilizing force, in particular for finite Reynolds number flows, few focus on the case of a liquid film below a substrate. Here we focus on non-inertial films with a destabilizing gravity. This case is relevant for the very thin film dynamic (geophysics of cave, morphogenesis, engineering of cooling system) as well as viscous films (glass flows, etc.). This system relates to the Rayleigh-Taylor instability of a thin film where the substrate is now inclined. This inclination gives rise to a flow characterized by the flat film solution (so-called Nusselt solution) that undergoes an absolute/convective transition.
We built an experiment set-up that allows to produce a well-controlled continuous flow below a flat substrate. We can accurately vary the angle formed with gravity and the film thickness. We measure patterns in the surface height. These patterns are forced by the natural boundaries of the apparatus in convectively unstable situations. The experimental results are found to be in excellent agreement with 2D non linear numerical simulations of the lubrication equation. Thanks to the local linear stability analysis we show that the selected wavelength is not accurately predicted by the linear stability theory but involves the group velocity of each component of the wave packet that is forced by the sides and advected downstream. From simulations in a periodic domain, we observe a non linear selection mechanism of the patterns which is then confirmed by experiments.

 

Practical information

  • General public
  • Free

Organizer

  • MEGA.Seminar Organizing Committee

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Tags

Solids Structures Fluids

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