The numerical simulation of liquid sloshing in microgravity

The numerical simulation of liquid sloshing in microgravity

Luppes, R.
Helder, J.A.
Veldman, A.E.P.

2006-09-07

With the increasing amount of liquid on board spacecraft, liquid management and its influence on the overall spacecraft dynamics is becoming increasingly important. The influence of sloshing liquid may hamper critical manoeuvres in space, such as the docking of liquid-cargo vehicles (e.g. to ISS) or the pointing of observational satellites. Severe problems with sloshing liquid in space have been reported. The experimental study of the interaction between liquid sloshing and spacecraft dynamics, by means of droptower or parabolic flight, is difficult because of the short duration of terrestrial free fall. Therefore, experiments have been carried out with the NLR-built satellite 'Sloshsat FLEVO' in an orbit around earth. During the experiments, several relevant quantities for the Sloshsat motion were measured. The experiments with Sloshsat were supported by a theoretical/computational model based on the Navier-Stokes equations for 3D incompressible free-surface flow. This Computational Fluid Dynamics (CFD) model called ComFlo, developed at RuG since the 1990's, includes capillary surface physics as well as coupled solid-liquid interaction dynamics. By means of this model, more insight can be gained in the relevant physics that plays a part in the interaction between liquid sloshing and overall spacecraft dynamics. In the absence of gravity, capillary effects at the free liquid surface, such as surface tension and wetting characteristics, are dominating liquid motion. Experimental results and numerical simulations are compared. The obtained frequencies in angular velocities are reasonably comparable at various rotational rates during various satellite manoeuvres. This means that in the numerical model, the sloshing frequency of the water inside the tank is adopted correctly by the satellite motion. The damping of the nutation amplitudes, observed in the simulations, is too large, as a result of additional numerical diffusion in the computational model. As this effect depends on the magnitude of fluid velocity, it is most visible at experiments with large rotational velocities and fluid velocities. At low rotational rates and small-scale liquid motion, capillary effects are important for the obtained damping of manoeuvre-induced oscillations in the angular velocities. In case of large-scale liquid motion, such as obtained during flat-spin manoeuvres, capillary forces are less important.

free-surface flows
microgravity
solid-liquid interaction
Sloshsat FLEVO
numerical simulations

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Conference proceedings

conference paper

(c) 2006 Luppes, R.; Helder, J.A.; Veldman, A.E.P.