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).