The oscillation of liquid/gas free surface in a partially filled storage tank caused by an abrupt drop of gravity level is of critical importance for the fluids management in space. In present study we investigate the dynamic behavior of free surface in tank models (tubes) using water as the working medium utilizing the Drop Tower Beijing, which can provide a 3.6s short-term microgravity condition. Meanwhile, the corresponding numerical simulation using volume of fluids (VOF) methods was carried out. It is shown that the dynamic behavior of free surface, which belongs to the typical phenomenon of capillary flow, is affected by the properties of working medium and the geometry and surface properties of the storage tank (especially the contact angle) jointly. The numerical simulation could capture the major characteristic oscillation frequency of free surface revealed by experiment. The oscillation frequency of free surface increases with the increasing air fraction and remains nearly constant at large air fraction. For the same air fraction, the oscillation frequency significantly increases with the decreasing tank diameter.

Gravity affects the stability of Marangoni flow in floating half zone of low-Pr fluids through two different factors, i.e., the buoyancy and the static deformation of the free surface shape. In the present study, influence of these two factors are evaluated by unsteady three-dimensional (3D) simulations for a realistic model of floating half zone of molten tin (Pr<!-- --> <!-- -->=<!-- --> <!-- -->0.009) with an aspect ratio As<!-- --> <!-- -->=<!-- --> <!-- -->2.0 under a ramped temperature difference (1.19<!-- --> <!-- -->K/min) between the top and bottom ends of two iron supporting rods. The corresponding first critical conditions for the onset of 3D asymmetric non-oscillatory flows and the second critical conditions for the onset of 3D oscillatory flows are determined. Simulation results indicate that the fee surface deformation is the most influential factor for the critical conditions of the flow transitions. Buoyancy is less influential to the flow transitions. However, buoyancy causes multiple step transitions between different 3D asymmetric non-oscillatory flow modes.