Séminaire de Mécanique d'Orsay

Le Jeudi 17 avril à 14h00 - Salle de conférences du FAST

Levitation of a drop over a moving surface

Henri Lhuissier
MSC, Université Paris Diderot

A drop gently deposited onto the inner wall of a rotating hollow cylinder may not make contact with the wall. For a sufficient velocity of the wall, the drop steadily levitates over a thin air film and reaches a stable angular position in the cylinder, where the drag and lift balance the weight of the drop. Interferometric measurements yield the three-dimensional air film thickness under the drop and reveal the asymmetry of the profile along the direction of the wall motion. A two-dimensional model explains the levitation mechanism, captures the main characteristics of the air film shape and predicts two asymptotic regimes for the film thickness h : For large drops h ∼ Ca^(2/3)/K, as in the Bretherton problem, where Ca is the capillary number based on the air viscosity and K is the curvature at the bottom of the drop. For small drops h ∼(Ca a K)^(4/5)/K, where a is the capillary length.