  We investigate the levitation of a drop gently deposited onto the inner wall
of a rotating hollow cylinder. 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 measurement yields the three-dimensional (3D) air film
thickness under the drop and reveals the asymmetry of the profile along the
direction of the wall motion. A two-dimensional (2D) model is presented which
explains the levitation mechanism, captures the main characteristics of the air
film shape and predicts two asymptotic regimes for the film thickness $h_0$:
For large drops $h_0\sim\ca^{2/3}\kappa_b^{-1}$, as in the Bretherton problem,
where $\ca$ is the capillary number based on the air viscosity and $\kappa_b$
is the curvature at the bottom of the drop. For small drops
$h_0\sim\ca^{4/5}(a\kappa_b)^{4/5}\kappa_b^{-1}$, where $a$ is the capillary
length.

Fluid Dynamics