Fluid behavior in microgravity is different from that in normal gravity since surface tension and wetting are dominant in microgravity. In propellant tanks for future in-orbit spacecraft, sloshing due to disturbance and a settling behavior from changes in acceleration must be understood for the design of the propellant supply system and attitude control system. As a target to understand the liquid behavior when the tank is accelerarated and decelerated in the second-stage rocket propulsion system, this study investigated the liquid behaviors in the cylindrical test tank via microgravity experiments and numerical calculations when the acceleration was applied in the axial direction in microgravity. The effects of acceleration direction (upward and downward), magnitude, and tank size on liquid behavior were clarified. As a result, it was shown that the experimental results agreed with the analytical ones when a large downward axial acceleration was applied, in which the liquid film on the solid wall became thicker. On the other hand, when the axial acceleration was small and the applied direction was upward, the breakage of the liquid film on the solid wall occurred in the numerical calculation, which was not observed in the experiment. From these results, it was shown that it was important to realize the thin liquid film on the solid wall surface by numerical calculations. Furthermore, based on the obtained knowledge, the effect of the liquid behavior under acceleration on the second-stage rocket propulsion system was considered.
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