| Summary: | 碩士 === 大葉大學 === 機械工程學系碩士班 === 91 === The surface-tension type propellant tank is generally adopted in the baseline design of 500-kg class satellites. For this specific type of propellant tank, there is no diaphragm to physically separate the liquid hydrazine (N2H4) from the pressurant gas (typically N2 or He). In response to different mission requirements, the change of satellite attitude configurations could lead to the excitation of the time-dependent liquid sloshing flows inside the tank. Those sloshing waves along the liquid-gas interface can further induce considerable fluctuations of fluid stress and its disturbance moment exerted on the inner walls of the tank. In addition, under the situations of large-amplitude sloshing waves and some particular attitude modes, the pressurant gas bubble can be settled over the tank outlet prior to thruster restart, likely causing the gas entrainment into the propellant supply line with the worst consequence of the degradation or even failure for the propulsive performance. The objective of this research is to set up a free-falling tower to observe dynamical behavior of liquid-gas interfaces and the distributions of liquid in a transparent sphere under low-gravity environments. Theoretically, the time-dependent interfacial transport behavior has been formulated using the conservation equations of mass and momentum in conjunction with the VOF-PLIC (Volume of Fluid-Piecewise Linear Interface Construction) method. The CFS (Continuum Surface Force) model was adopted to treat the surface tension effect on the liquid-gas interface movement. Numerical calculations were performed using the SIMPLEC (Semi-Implicit Method for Pressure-Linked Equations Consistent) scheme. The predictions are in reasonable agreement the experiment showing the validity of the present theoretical model. For ROCSAT-2 propellant tank, various effects including liquid filled ratio, gravity level, surface tension, and contact angle on the spatial distribution of the gas bubble shape also has been examined detail.
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