Investigation of liquid-gas interfacial shapes in reduced gravitational environments

The objective of this study was to investigate the liquid-gas interfacial shapes in a low-gravity environment. Experimentally, a free-falling test setup was established to perform drop tests for observing interfacial flow phenomena under reduced-gravity conditions. In the theoretical analysis, the complex two-phase flowfield was simulated by using the transient three-dimensional conservation equations of mass and momentum. The continuous surface force (CSF) model was adopted to treat the surface-tension effect at the liquid-gas boundary. The volume-of-fluid (VOF) method, together with the piecewise linear interface construction (PLIC) technique, was used to describe the liquid-gas interface movements. The predictions were compared with the photographed images of the water-air interface shapes to validate the present computer code. To extend the application to the internal flow study of a ROCSAT-2 propellant tank, 16 numerical experiments were conducted to examine various effects, including liquid-filled ratio, gravity level, surface tension, and contact angle on the equilibrium shape of the pressurized helium gas bubble and the location of the center of mass (CoM).