Simulation of sloshing and settling behavior of liquid hydrogen in an insulated tank during coastal period

Abstract

Axial acceleration changes significantly after the rocket's main engine cutoff, which may result in severe propellant sloshing and consequent safety threats. Suppression of liquid propellant slosh is crucial. A comprehensive understanding of the sloshing behavior will benefit the design of the settling thrust, retention force, and retention engine start time. The sloshing behavior and settling characteristics of liquid hydrogen in a large tank with a height of 10.06 m and a diameter of 3.05 m during the coastal period was studied. It is proved that using a single Bond number for similarity scaling is incorrect. A criterion was proposed for evaluating the effect of propellant settling activity, which is described as “Settling is accomplished when the volume fraction of liquid phase in the top region with 10% of the tank height falls below a threshold value”. The results indicated that the settling achieves satisfying effect when the thrust exceeds 8 × 10⁻³ g. The force exerted by the tank on the fluid had a significant impact on the settling performance, which has been overlooked in early studies. Higher initial residual slosh degree leads to shorter settling times. The propellant settling phase should last for a sufficiently long time before the starting of the retention engine to avoid the liquid propellant returning to the top of the tank again. This study provides guidelines for the design of settling thrust system operated during the coastal period of a spacecraft.