Study on the shape and motion of bubbles in the tank model with a central column aboard the Chinese Space Station

Abstract

It is of great significance for fluid management under microgravity to explore the morphological characteristics of annular bubbles in a tank with a central column. The propellant residue can be evaluated by measuring the annular bubble's volume, and the estimation of the mass center of tanks also needs to know the liquid distribution. An experiment cabin is designed and the experiments of filling and emptying the tank model are carried out aboard the Chinese Space Station. Two kinds of annular bubbles surrounding the central column under microgravity are observed experimentally for the first time, which appear during the processes of filling and emptying the tank model, respectively. Furthermore, the profiles of these annular bubbles are obtained by theoretical derivation. Numerical procedures based on the theoretical expressions are developed and the bubble profiles can be predicted in few seconds. The evolutions of the movement and shape of small bubbles are also explored experimentally and numerically. Under the constraint of minimum free surface energy, several small spherical bubbles will merge into a bigger spherical bubble, which are driven by small disturbances and their initial velocities, and the bigger bubble will locate in the middle region of the tank model at equilibrium. When the volume of the bubble keeps increasing, the surface of the bubble will become the specific Delaunay interface, whose the mean curvature is constant, under the constraints of the propellant management device and the tank wall.