Understanding interfacial dynamics and fluid physics is important in many engineering applications, including spacecraft. Under microgravity, the moving boundaries and associated interfacial transport processes significantly impact the vehicle dynamics, design, and missions. However, it is difficult to mimic the micro-gravity condition experimentally. Numerical simulations of such problems are also challenging due to multiple time/length scales, large variations in fluid properties, moving boundaries, and phase changes.

A 3-D adaptive Eulerian-Lagrangian method is implemented for multiphase flow computations. The stationary (Eulerian) Cartesian grid is used to resolve the flow field, and the marker-based triangulated moving (Lagrangian) surface meshes are utilized to treat the phase boundaries. A main focus of the present study is to treat both fluid and solid phase boundaries in a unified framework with a contact line force model and a phase change model. The fluid interfaces are modeled using a continuous interface method which smoothes both the variations in material properties and the influences of surface tension. The solid boundaries are treated by a ghost cell-based sharp interface method. A dynamic contact line force model is applied to calculate the position and movement of the solid-fluid-fluid interface. The energy and mass transfer due to phase change is computed using Stefan condition across the interfaces. A multi-level adaptive grid method is devised so that different length scales of the flow field can be resolved effectively.

Selected studies on the interfacial dynamics relevant to spacecraft fuel delivery applications are conducted and assessed with experimental measurements and scaling analysis. For liquid fuel draining under microgravity, depending on the relative influence between capillary force and inertia force, three different flow regimes are observed and liquid residuals are measured. The liquid fuel sloshing under varying acceleration results in a large shift in its center of mass and significant influence on the vehicle dynamics. For thrust oscillation studies, the liquid surface stability under vertically oscillating acceleration is investigated, and the threshold acceleration is correlated with the forcing frequency, surface tension, and viscosity. For thermo-fluid transport computations with phase changes, validation studies are conducted with natural convection flows, Stefan problems, and melting processes by convection/diffusion flows.