  The motion of a gas-liquid interface along a solid wall is influenced by the
capillary forces resulting from the interface's shape and its interaction with
the solid, where it forms a dynamic contact angle. Capillary models play a
significant role in the management of cryogenic propellants in space, where
surface tension dominates the behaviour of gas-liquid interfaces. Yet, most
empirical models have been derived in configurations dominated by viscous
forces. In this study, we experimentally investigate the wetting of a
low-viscosity, highly wetting fluid in a reduced gravity environment. Our setup
consisted of a transparent and diverging U-tube in which capillary forces
sustain the liquid motion. Combining Particle Image Velocimetry (PIV) and
high-speed backlighting visualization, the experimental campaign allowed for
measuring the interface evolution and the velocity field within the liquid
under varying gravity levels. This work reports on the preliminary results from
the image velocimetry and shows that the velocity profile within the tube is
close to parabolic until a short distance from the interface. Nevertheless,
classic 1D models for capillary rise face difficulties reproducing the
interface dynamics, suggesting that the treatment of the surface tension in
these problems must be reviewed.
