Hydrodynamics of Intermediate-Scale Taylor Flow under Gravities of Space Colonies

Abstract

This paper investigates the effect of gravitational strength on hydrodynamics of intermediate-scale Taylor bubble in vertical upward slug flow. Air and water were used as the working fluids and two different sets of superficial velocities (JL = 0.05, JG = 0.15 m/s; and JL = JG = 0.15 m/s) were carefully selected to create laminar slug (Taylor bubble) flows. In order to effectively study the gravitational influence with a reasonable computational cost, an intermediate-scale tube diameter (D = 12 mm) was selected. The governing equations were discretized in a three-dimensional computational domain and numerically solved based on the volume of fluid-continuum surface force (VOF-CSF) method using OpenFOAM. The computational fluid dynamics (CFD) model was validated under normal gravity with existing top performing correlations in literature. To address the space colonization environments, the gravity strength considered in the CFD simulations include 10−4go (microgravity), 0.17go (Moon), 0.38go (Mars), go (=9.81 m/s2, Earth), and 2go (hyper). The simulation results show that by increasing gravity, Taylor bubbles of the slug flow are shrunk both in length and diameter leading to a reduced void fraction. The flow field around Taylor bubbles was found to be significantly affected by gravitational strength. A strong falling-film flow around a Taylor bubble was observed at the hyper-gravity, while no falling-film flow existed at microgravity. The falling-film flow caused a local reversal of wall shear stress, and thus a positive frictional pressure gradient that was intensified by increasing gravitational strength. However, the total pressure gradient including a hydrostatic pressure always were negative despite the positive frictional pressure gradient. The rising velocity of the Taylor bubble exhibited an interesting behavior showing a minimum around normal gravity.