Seminarium Zakładu Mechaniki i Fizyki Płynów "Hydrodynamic slip and suspensions" prof. Francois Feuillebois, Laboratoire PMMH, CNRS UMR 7636 ESPCI, Paris, France środa, 19 października 2005

Hydrodynamic slip on a surface may occur at various scales for suspensions of particles in a viscous fluid. First, there is the slip of a fluid on a surface which occurs at the molecular scale. For hydrophobic surfaces, the slip length is even above the molecular scale. A technique of measurement of fluid velocity at sub-micron scale will be presented. Second, for rough surfaces a equivalent smooth surface enveloping the roughness may be defined. The fluid then appears to slip on this surface. Measurements and modelling of a slip length will be presented. Third, at the level of an ensemble of particles, the suspension appears to slip on a surface. This effect is involved in the "intrinsic convection" when in sedimentation in a vertical container. It also appears in the derivation of an effective viscosity of a suspension in the vicinity of a wall.