CFD analysis of stratification during draining of a sub-scaled liquid hydrogen tank

Thermal stratification occurring inside a cryogenic flight tank leads to failure in meeting the NPSH requirement of the pumps and thus affects smooth operation of onboard turbo machinery, particularly towards the end of a mission, resulting in a large residual quantity of propellants. Therefore, understanding the phenomenon of stratification is an important aspect of launch vehicle design. Towards this, analysis has been done on a sub-scaled liquid hydrogen tank simulating stratification in a low heat in-leak environment. Computational Fluid Dynamics (CFD) has been applied for understanding the liquid dynamics of the process over a sufficiently long duration. The model utilizes a two-dimensional axisymmetric approach along with the volume of fluid (VOF) scheme to simulate the liquid vapour interface. The effect of stratification on propellant draining has been analysed for two different intake systems, with and without a propellant intake device (PID), and the corresponding residual quantities verified. The analysis confirmed that with a PID, the residual propellant quantity can be minimized.