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Low-G Capillary Draining in Grooves and Sloshing Liquids

In space, surface tension (not gravity) dominates fluid displacement, where fluid wicks through vein networks via grooves. Groove geometries are prevalent aboard spacecraft fluid systems and fuel containment chambers. In such systems, it is crucial propellants and cryogens are available at drain ports when needed. Then it is critical to understand drain rates to ensure space systems function predictably. Flow containment is also critical, as unpredictable residual accelerations (crew docking, orbital maneuvers, etc.) can induce flow instability and lead to bubble formulations and occlusions which, for example, in 2002 shut down an oxygen generator aboard the International Space Station (ISS). Understanding low-g flow sloshing and drain rates ensure spacecraft function properly and offer design advantages to propellant management devices.

The work we present is in two parts: first we analyze experimental low-g draining from interior corner grooves via video data from the ISS, a two phase air - silicone oil experiment. We then compare this data to 3D simulations in OpenFOAM. We also analyze liquid sloshing in a rectangular channel conducted at a terrestrial lab at length scales smaller than the capillary length scale (2mm). We compare the sloshing frequencies observed to those predicted by simulations of liquid sloshing in a 2D rectangular channel in OpenFOAM. Theoretical predictions are also made and assessed in light of experiments and simulations, using spectral methods and the lubrication approximation. The Bond number Bo < 1 and the Weber number We ~ O(1) are the regimes of interest, where surface tension balances inertia. Finally we compare simulations with various artificial compression factors (cAlpha) to both theory and experiments through the interFoam solver.