Sloshing Behaviour of Liquid Nitrogen in a Large Scale Cryogenic Tank Demonstrator

Abstract

The knowledge about the behaviour of the propellant in tank systems is of crucial importance for the design of spacecraft. The sloshing of liquid propellants is of direct importance for the flight stability since the sloshing forces may input the flight direction and altitude of the spacecraft. For the prediction of the sloshing behaviour in addition the sloshing frequency and the damping behaviour has to be known. In case of cryogenic liquids additional thermodynamic effects have to be considered which can have an effect on the tank pressure. To investigate the sloshing phenomena, as well as to generate an experimental data base for tool validation, sloshing tests with liquid nitrogen have been performed with the ArianeGroup Cryogenic Tank. The aim of this study is to determine the damping behaviour of liquid nitrogen in the ArianeGroup Cryogenic Tank for various fill levels and excitations. The tank demonstrator is mounted on a hexapod system and is equipped with a fill level sensor, an acceleration sensor and a force measurement system. During the tests, first the liquid is forced to a defined sinusoidal motion. After stop of excitation the sloshing forces and liquid motions are recorded and evaluated. The results show a strong influence of the damping behaviour on the sloshing angle. The damping varies during decaying movement and decreases with decreasing sloshing angle. The large tank radii, in conjunction with the low viscosity of the cryogenic liquid, lead to a significant increase in the Galilei number. In addition, turbulent effects are promoted in large tank systems due to the higher fluid velocities paired with low viscosity in case of sloshing. The influence of the sloshing angle on the damping behaviour is presented and discussed. The experimental results are compared with state of the art correlations from the literature.