Super-diffusion in sheared suspensions

Mathieu Souzy (1) , Xiaolong Yin (2) , Emmanuel Villermaux (3) , Chérifa Abid (1) , Bloen Metzger (1)

1 IUSTI - Institut universitaire des systèmes thermiques industriels
2 Colorado School of Mines
3 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre

We investigate the dispersion of a layer of dye initially applied at the outer wall of a cylindrical Couette-cell into a sheared suspension of non-Brownian spherical particles. The process is directly visualized and quantified at the particle scale. A “rolling-coating” mechanism is found to convectively transport the dye at a constant rate directly from the wall towards the bulk. The fluid velocity fluctuations, u′, measured with particle image velocimetry, and the imposed shear-rate, γ, are used to define a diffusion coefficient, D∝ ⟨u′u′⟩/ γ, which is found to increase linearly with the distance from the wall. A solution of the transport equation accounting for this inhomogeneous stirring field describes quantitatively the concentration profiles measured experimentally. It exhibits a super-diffusive character, a consequence of the increase of the stirring strength with distance from the wall. Movies are available with the online version of the paper.

Mots clés: Particulate suspension; low Reynolds number; dispersion

Domaines: Mécanique des fluides [physics.class-ph]

Mathieu Souzy, Xiaolong Yin, Emmanuel Villermaux, Chérifa Abid, Bloen Metzger. Super-diffusion in sheared suspensions. Physics of Fluids, 2015, 27 (4), pp.41705 ⟨10.1063/1.4918613⟩. ⟨hal-01449403⟩