Séminaire de Masoud Moazzen (IMT Nord Europe, Douai)

Torque dynamics in Taylor-Couette flow of complex fluids: from viscoelastic solutions to particle suspensions

Masoud Moazzen, IMT Nord Europe, Douai

Complex fluids are found in many applications (agricultural cosmetics, etc..) as well as in nature. Due to the presence of intermediate scale elements, called mesoscopic, they do not show a linear response to the exerted stress. Fundamental studies in a simplified geometry are necessary to understand the stability and flow regimes of these types of fluids. In this study, we chose to use the Taylor-Couette (TC) geometry consisting of two coaxial cylinders, positioned vertically, with the inner cylinder rotating and the outer cylinder stationary. We studied, in TC flow, two types of complex fluids: non-colloidal suspensions of solid particles in a Newtonian matrix, and viscoelastic solutions of diluted polymer. Using a TC system mounted on a rheometer allows a direct visualization of the flow simultaneously with the torque measurement, and thus the experimental characterization of the Spatio-temporal and frictional properties of the flows. For viscoelastic fluids, we show that a chaotic flow state called elasto-inertial turbulence is triggered at low Reynolds number and presents very specific frictional properties, very different from inertial turbulence. For suspensions, we notice a modulation of the transition sequences (appearance of non-axisymmetric regimes, variable range of existence), as well as scaling laws of the friction-based pseudo Nusselt number. These indicators allow to define several hydrodynamic sub-regimes depending on the particle concentration.

-----------------------------------------------------------------------------------------------

Video recordings of the meeting : : https://nextcloud.univ-lille.fr/index.php/s/KayLQG8rExpB89d