Speaker
Description
Storage and transfer of propellants in space will become a primary requirement for future long-range long-term space missions. A propellant depot can store the propellants in space and thereby help in refilling the tanks of the docked spacecrafts. It is challenging to understand the flow physics related to storage and refuelling in orbit. While in normal gravity the free surface remains flat for a tank filled with liquid, in microgravity capillary forces dominate and lead to a new configuration of the free surface. Propellant management devices help in controlling the shape and position of the free surface in microgravity. Loss of propellant can be reduced and self-pressurization of tanks can be controlled if the stability of the free surface in microgravity during the filling of a tank is known.
In this work, the experimental results from the drop tower experiments that were carried out at the ZARM drop tower with a microgravity time of 9 seconds are presented. An experiment tank is filled with test liquid HFE-7500 to an initial fill height. The behaviour of the free surface and its interaction with an incoming liquid during the filling of the tank is investigated for different volumetric inflow rates. After an initial period of liquid reorientation inside the tank, the filling process is started. The free surface behaviour is tested for two inlet configurations of the experiment tank, which are the central and the lateral inlet. The incoming liquid jet directly touches the free surface when using the central inlet. For the lateral inlet, the presence of a velocity control plate (VCP) dissipates the linear momentum of the incoming liquid into the bulk liquid.
The behaviour of the free surface can be classified into three regimes of subcritical, critical and supercritical flow. The non-dimensional Weber number can be used to represent the flow regimes. For the central inlet tests, the incoming liquid jet causes a perturbation of the free surface and forms a geyser in the subcritical range. The geyser that grows with time and disintegrates into droplets is observed in the critical range. For the supercritical regime, the liquid jet touches the outlet port at the top of the tank. For the lateral inlet tests, the free surface remains unperturbed during the filling, enabling a quiescent and faster filling of the tank. Different flow regimes during the filling of a tank in microgravity can be identified from these results so that depending on the application the corresponding regime can be chosen. Furthermore, based on these drop tower experiment results, a space station experiment can be designed and planned.
| Keywords | free surface stability, liquid filling in microgravity, drop tower experiment |
|---|
