Laboratoire de Mécanique des Fluides et d'Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique

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Proposition de thèse au LMFA

PhD proposal, beginning in October 2018

Proposition de thèse au LMFA

Role of surfactants on break-up and deformation

The objective of this thesis is to determine, in comparatively small-scale experiments, the role of surfactants on the deformation and breakup of single bubbles and droplets in the presence of strong inertial effects. While much is known about the role of surfactants in quasi-steady systems (often in Stokes flow), we are interested here in the role of interface rheology under more general flow conditions.
Two experimental configurations will be studied :
- Deformation and breakup of single bubbles in rotating flows. The first experimental set-up has already been developed and used in prior work at LMFA for bubbles in rotating liquids (Rastello 2009, 2011, 2017). It is constituted by a cylindrical tank (Ø=10 cm, L=10 cm) rotating around a horizontal axis, such that buoyancy can be balanced by the rotating flow. When the rotation of the flow is stationary, all the forces acting on the bubble balance and the bubble comes to an equilibrium point. The procedure will consist in filling the tank with successive fluids containing various concentrations of surfactant and investigate interface deformation. The resulting interface shape will be visualized by high-speed imaging in the plane perpendicular to the axis of rotation. We shall also undertake to measure the velocity around the bubble/droplet with PIV, in order to facilitate interpretation of the interface shape evolution.
- Fragmentation of droplets, bubbles and jets in shear In the second experiment, built during the thesis, we will investigate the impact of surfactants on the break-up of an inclusion under shear in inertial conditions : we will first study the break-up of a single droplet/bubble, and then the break-up of a jet. The inclusion will be issued into a closed reservoir filled with liquid, directly between four rotating rolls. The aim is to capture how shear-induced break-up is impacted when surfactant is added into the liquid. This will be studied with a gas jet/bubble, or with a liquid (oil) jet/droplet.
Comparison with numerical simulations
The results obtained on the above experiments will be confronted to the results of a numerical simulation, using an existing computing code (collaboration with ILM, Lyon). The thesis will be carried out at the LMFA (Laboratoire de Mécanique des Fluides et d’Acoustique), in Ecully. It is funded by the ANR, as part of project SURFBREAK in collaboration with ILM (Lyon) and LEGI (Grenoble).

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