Title : Particle dynamics : From microplastics in the ocean to complex fluids
Contact : Marie Rastello
Abstract : During this seminar, I will mainly present the result of my PhD on the vertical dynamics of buoyant particles in anisotropic turbulence, whose direct application is the microplastic (1 µm<L<5mm) pollution in the ocean. I will also present my current post-doctoral research, on the development of an ultrasound technique to probe the microstructure of dense suspensions. For this purpose, a coupling between ultrasound and optical measurements (refractive index matching between the particles and the fluid) has been set up.
Details on the dynamics of particles in turbulence :
Often less dense than seawater, microplastics are mixed under the surface due to a surface stirring induced by wind and waves. Thanks to an analysis of samples collected at sea, a model, taking into account the properties (density, size, and shape) of micro-plastics is first proposed, to better predict their buoyancy. Then, laboratory experiments using an oscillating grid system have been used to reproduce the surface mixing induced by wind and waves. The transport of idealized plastics (spheres and disks) in this setup is investigated to identify the parameter which controls the coupling between the particles and the flow, the turbulent Schmidt number. We propose a value of it for microplastics, for the first time.