Low-Gravity Sloshing in Spherical Tanks: Experimental Investigation Toward Numerical and Analytical Modeling
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Silveri, Luca
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Abstract
Uncontrolled sloshing in spacecraft propellant tanks can severely disturb vehicle attitude and dynamics, jeopardizing critical proximity maneuvers. Despite decades of research, the dynamics of low-gravity sloshing remain insufficiently understood and difficult to model with reliability, also due to limited and incomplete experimental data. In this context, this thesis presents: (i) a new experimental dataset on low-gravity sloshing in a spherical tank; (ii) a numerical CFD framework and an analytical spherical pendulum model for simulating low-gravity free contact line fluid motion; and (iii) the development of numerical and analytical models for contact angle hysteresis. The experimental dataset, originating from the SILA (Sloshing Imaging and Load Analysis) payload, shows low- to large-amplitude sloshing in a spherical tank for a range of Bond numbers below 50. The force exerted on the tank walls is recorded, and the position of the center of mass is reconstructed from free surface tracking to analyze the fluid’s response in both time and frequency domains. Video imaging and Bond number evolution are reported to characterize the low-gravity environment and transitions between high and low gravity. A numerical setup is implemented in ANSYS Fluent and validated in microgravity for constant contact angles. The analytical model of the spherical pendulum is implemented in MATLAB, and the results for the center of mass displacement qualitatively match the numerical ones. Still, both deviate from the experimental data due to overly simplified free-contact-line assumptions. For the analyzed low-gravity range (Bo <50), the contact angle hysteresis is revealed as a fundamental physical factor that simplified pendulum analogies fail to simulate, thus invalidating their use in widespread spacecraft guidance, navigation, and control algorithms. The development of a User Defined Function for ANSYS Fluent modeling the contact angle hysteresis in both two and three dimensions is initiated, valid for structured grids and for surfaces of any shape. The development of a two-pendulum model is proposed to capture the dynamics given by the contact angle hysteresis.
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2025-12
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Thesis (Masters Degree)