Drop impact of yield-stress fluids

Abstract

International audienceThe normal impact of a drop of yield-stress fluid on a flat rigid surface is investigated experimentally. Using different model fluids (polymer microgels, clay suspensions) and impacted surfaces (partially wettable, super-hydrophobic), we find a rich variety of impact regimes from irreversible viscoplastic coating to giant elastic spreading and recoil. A minimal model of inertial spreading, taking into account an elasto-viscoplastic rheology, allows explaining in a single framework the different regimes and scaling laws. In addition, semi-quantitative predictions for the spread factor are obtained when the measured rheological parameters of the fluid (elasticity, yield stress, viscosity) are injected into the model. Our study offers a means to probe the short-time rheology of yield-stress fluids and highlights the role of elasticity on the unsteady hydrodynamics of these complex fluids

Giant Drag Reduction in Complex Fluid Drops on Rough Hydrophobic Surfaces

“…This means that bulk rheological properties and not surface tension are responsible for the arrest of the spreading in our study. In a previous work [16], we have shown that for a soft yield-stress fluid like Carbopol, elasticity controls the impact dynamics even above the yield stress, because the impact time is much shorter than the fluid relaxation time (large Deborah numbers). In Fig.…”

“…The first one is the capillary length scale =V 2 0 . The second is a viscous length scale defined as L 0 =Re [24], where Re is an effective Reynolds number of the Carbopol drops computed from the steady-state rheology of the fluid [16]. Figure 3(c) shows a good collapse of the data when is normalized by the capillary length scale, that is, using a Weber number based on the roughness size: V 2 0 = ¼ ð=L 0 ÞWe.…”

Impact simulation by an Eulerian model for interaction of multiple elastic-plastic solids and fluids

“…In particular, a symmetric copper rod impact is computed and compared to the experimental data provided in [9]. Then, a low velocity clay suspension impact is studied and compared to the experimental results obtained in [19].…”

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

“…As a consequence, it has become possible to explore in unprecedented detail the influence of a wide range of physical parameters on various stages of drop impact and to systematically compare experiment and theory 5,[13][14][15][16] . For instance, the splashing transition in Newtonian fluids was found to be set by atmosphere pressure 5 , while the intrinsic rheology decides the spreading dynamics of yield-stress fluids 17 .…”